Medicine – Tuberculosis

Tuberculosis (TB) is a chronic infectious disease caused predominantly by Mycobacterium tuberculosis. It is transmitted mainly through inhalation of airborne particles from a person with infectious pulmonary or laryngeal TB. Although the lungs are the most commonly affected organs, TB can disseminate and involve almost any part of the body.

1. Groups at Increased Risk

The risk of TB is determined by both the likelihood of exposure to M. tuberculosis and the likelihood that latent infection will progress to active disease.

People who have migrated from countries where TB is highly prevalent have an increased risk, particularly during the first several years after migration.

HIV Infection and Immunosuppression

HIV infection is an especially important risk factor because impaired cell-mediated immunity greatly increases the probability that latent TB will reactivate and that newly acquired infection will progress rapidly.

Other forms of immunosuppression, including corticosteroids, transplantation, chemotherapy, and anti-TNF therapy, also increase the risk of active and disseminated TB.

Social Risk Factors

People experiencing homelessness, overcrowded living conditions, poverty, incarceration, or poor access to healthcare may have increased exposure and delayed diagnosis.

Alcohol dependence and substance-use disorders can also increase risk through associated socioeconomic factors, malnutrition, impaired immunity, and difficulty completing treatment.

Primary Tuberculosis

2. Initial Infection

Primary TB refers to infection occurring in an individual who has not previously developed specific immunity to M. tuberculosis.

Inhaled organisms reach the distal airways and alveoli, where they are taken up by macrophages. The infection may initially produce few or no symptoms.

3. Ghon Focus

The initial pulmonary lesion is traditionally called the Ghon focus.

It is usually a small area of granulomatous inflammation located in the peripheral lung, often in the lower part of an upper lobe or upper part of a lower lobe.

4. Lymphatic Spread

Mycobacteria can travel from the initial pulmonary focus through the lymphatic vessels to the regional hilar lymph nodes.

The combination of the pulmonary Ghon focus and involved regional lymph nodes is known as the Ghon complex.

5. Arrest of Primary Infection

In most immunocompetent individuals, an effective cell-mediated immune response develops and controls the infection.

The organisms may be contained within granulomas rather than completely eliminated. Viable bacilli can therefore remain dormant for many years, producing latent TB infection.

6. Development of an Immune Response

After infection, immune sensitisation to M. tuberculosis develops.

A tuberculin skin test (Mantoux test) may therefore become positive several weeks after infection. Interferon-gamma release assays (IGRAs) can also demonstrate immunological sensitisation to TB.

Importantly, these tests indicate TB infection or immune sensitisation but cannot by themselves distinguish latent infection from active TB disease.

7. Clinical Features of Primary TB

Primary infection is frequently asymptomatic.

When symptoms occur, they may include mild fever, cough, fatigue, and occasionally wheezing when enlarged hilar lymph nodes compress an airway.

Erythema nodosum can occur as an immunological reaction to primary TB, although it has many other possible causes.

Post-Primary Tuberculosis

8. Reactivation Disease

Post-primary, or secondary, TB commonly results from reactivation of previously dormant organisms, although reinfection can also occur.

Reactivation is particularly likely when cell-mediated immunity becomes impaired because of ageing, malnutrition, HIV infection, immunosuppressive therapy, or other illnesses.

9. Upper-Lobe Predominance

Post-primary pulmonary TB classically affects the apical and posterior regions of the upper lobes.

These regions have relatively high oxygen tension, which favours growth of M. tuberculosis, an obligate aerobe.

Tissue destruction can lead to caseation and cavitation, allowing large numbers of bacilli to enter the airways and increasing infectiousness.

Miliary Tuberculosis

10. Haematogenous Dissemination

Miliary TB occurs when M. tuberculosis spreads widely through the bloodstream.

This produces numerous tiny granulomatous lesions in multiple organs. The term miliary describes the characteristic appearance of innumerable small lesions resembling millet seeds.

11. Organ Involvement

Miliary TB may involve the lungs, liver, spleen, bone marrow, kidneys, meninges, and other organs.

It is particularly important in young children and immunocompromised individuals but can occur at any age.

Clinical Features

12. Constitutional Symptoms

Active TB commonly produces constitutional symptoms including fever, drenching night sweats, loss of appetite, fatigue, and unintentional weight loss.

The onset may be gradual, with symptoms developing over weeks or months.

13. Cough

Persistent cough is a common manifestation of pulmonary TB.

It may initially be dry but can become productive as pulmonary disease progresses.

14. Haemoptysis

Haemoptysis can occur when cavitating disease or chronic inflammation damages pulmonary or bronchial blood vessels.

Bleeding ranges from minor blood-streaking to potentially life-threatening haemoptysis.

15. Pleural Effusion

TB can involve the pleura and produce a tuberculous pleural effusion.

The fluid is usually an exudate with lymphocyte predominance. Pleural fluid glucose may be reduced, particularly in more intense or chronic disease.

16. Tuberculous Meningitis

Dissemination to the central nervous system can produce tuberculous meningitis, a severe form of extrapulmonary TB.

Patients may develop persistent headache, fever, vomiting, altered consciousness, cranial nerve abnormalities, and neurological deficits.

Early recognition and treatment are essential because neurological complications can be permanent.

Diagnosis

17. Chest Radiograph

In post-primary pulmonary TB, the chest radiograph may demonstrate upper-zone or apical opacification, volume loss, fibrosis, and cavitation.

Primary TB may instead show hilar lymphadenopathy, consolidation, or pleural effusion.

Miliary TB classically produces innumerable tiny bilateral pulmonary nodules.

18. Sputum Examination

Patients suspected of having pulmonary TB should have respiratory samples examined for acid-fast bacilli (AFB).

Traditionally this involved sputum smear microscopy followed by mycobacterial culture.

Modern diagnosis increasingly incorporates rapid molecular tests, which can detect M. tuberculosis DNA and, depending on the assay, identify important drug-resistance markers much faster than conventional culture.

19. Mycobacterial Culture

Mycobacterial culture remains important because it confirms viable organisms and allows detailed drug-susceptibility testing.

Traditional solid cultures may require several weeks, explaining the older teaching that cultures take at least six weeks. Modern liquid culture systems frequently produce results considerably sooner, although final negative cultures may still require prolonged incubation.

20. Urine Examination

Early-morning urine samples can be examined for mycobacteria when genitourinary TB is suspected.

Multiple specimens may be required because organisms are not continuously shed into the urine.

21. Tissue Biopsy

When extrapulmonary TB is suspected, tissue may be obtained from sites such as an enlarged lymph node, pleura, or other affected organ.

Histology may demonstrate caseating granulomatous inflammation, while the tissue can also undergo molecular testing and mycobacterial culture.

22. Bone Marrow Examination

Bone marrow aspiration or biopsy may occasionally be useful in suspected disseminated or miliary TB, particularly when patients have unexplained cytopenias or systemic illness.

It is not a routine investigation for uncomplicated pulmonary TB.

23. Bronchoscopy

Bronchoscopy with bronchial washing or bronchoalveolar lavage can provide diagnostic material when sputum cannot be obtained or remains negative despite strong suspicion of pulmonary TB.

Treatment

24. Standard Initial Therapy

For drug-susceptible active TB, standard treatment generally begins with four drugs, not three:

Rifampicin + isoniazid + pyrazinamide + ethambutol.

These are commonly abbreviated RIPE therapy.

25. Duration of Treatment

For uncomplicated drug-susceptible pulmonary TB, the traditional standard regimen consists of:

2 months: rifampicin + isoniazid + pyrazinamide + ethambutol.

Followed by 4 months: rifampicin + isoniazid.

This gives a total treatment duration of approximately 6 months, although treatment varies according to drug susceptibility, site of disease, response, comorbidities, and national guidelines.

TB meningitis and some other forms of extrapulmonary disease generally require modified and/or longer treatment.

26. Drug Resistance

The older approach of reserving ethambutol only for patients with HIV or people from areas with high resistance is no longer standard.

Four-drug initial therapy is generally used while drug susceptibility is being established, because isoniazid resistance may be present even without obvious risk factors.

Drug-resistant TB requires specialist treatment using regimens determined by molecular and culture-based susceptibility testing.

27. Importance of Adherence

Adherence to the complete treatment regimen is essential.

Poor adherence can result in treatment failure, relapse, continued transmission, and selection of drug-resistant M. tuberculosis.

Adverse Effects of Antituberculous Drugs

28. Rifampicin

Rifampicin can cause hepatotoxicity, gastrointestinal disturbance, rash, and orange-red discoloration of urine, sweat, saliva, and tears.

The discoloration of body fluids is harmless but patients should be warned about it.

Rifampicin is also a powerful hepatic enzyme inducer, producing clinically important interactions with numerous medications, including some anticoagulants, anticonvulsants, hormonal contraceptives, and antiretroviral drugs.

29. Isoniazid

Isoniazid can cause hepatotoxicity and peripheral neuropathy.

Neuropathy results partly from interference with vitamin B6 metabolism and can be prevented or reduced by giving pyridoxine (vitamin B6), particularly in patients at increased risk.

30. Pyrazinamide

Pyrazinamide can cause hepatotoxicity, gastrointestinal symptoms, rash, arthralgia, and hyperuricaemia.

The rise in uric acid may occasionally precipitate acute gout.

31. Ethambutol

The most important adverse effect of ethambutol is optic neuropathy, which can cause reduced visual acuity and impaired colour vision, classically affecting red-green discrimination.

Patients should have appropriate assessment of vision and be advised to report visual changes promptly.

Because ethambutol is largely eliminated through the kidneys, dose adjustment may be necessary in significant renal impairment. Renal dysfunction itself is not the classic toxicity of ethambutol.

Key Clinical Pattern

Think of pulmonary TB in a patient with persistent cough, weight loss, fever, night sweats and haemoptysis, particularly when imaging demonstrates upper-lobe disease with cavitation.

Remember the progression:

Primary infection → Ghon focus and regional lymph nodes → immune containment/latent TB → possible later reactivation as post-primary TB.

Miliary TB results from widespread haematogenous dissemination and can involve multiple organs.

For uncomplicated drug-susceptible pulmonary TB, remember RIPE for the initial 2 months, followed traditionally by rifampicin + isoniazid for another 4 months, with treatment adjusted according to susceptibility results and the clinical form of disease.

Medicine – Pleural Effusion

A pleural effusion is an abnormal accumulation of fluid within the pleural space. The key initial step is to determine whether the fluid is a transudate or an exudate, because this greatly narrows the differential diagnosis.

1. Classification of Pleural Fluid

The standard approach is to use Light’s criteria.

A pleural effusion is classified as an exudate if any one of the following is present:

• Pleural fluid protein : serum protein ratio > 0.5
• Pleural fluid LDH : serum LDH ratio > 0.6
• Pleural fluid LDH > two-thirds of the upper limit of normal serum LDH

If none of these criteria is met, the effusion is usually considered a transudate.

2. Transudative Pleural Effusion

A transudate is generally caused by a systemic disturbance in hydrostatic or oncotic pressure, rather than local pleural inflammation.

Cardiac Failure

Congestive cardiac failure is one of the commonest causes of transudative pleural effusion.

Raised pulmonary venous pressure increases hydrostatic pressure and drives fluid into the pleural space. Effusions are often bilateral, although one side may predominate.

Cirrhosis

Cirrhosis can cause pleural effusion, often through movement of ascitic fluid across small diaphragmatic defects.

This is sometimes referred to as hepatic hydrothorax and is commonly right-sided.

Hypoalbuminaemia

Marked hypoalbuminaemia reduces plasma oncotic pressure, favouring movement of fluid from the vascular compartment into tissues and body cavities, including the pleural space.

Nephrotic Syndrome

In nephrotic syndrome, heavy urinary protein loss causes hypoalbuminaemia and reduced oncotic pressure.

This can result in peripheral oedema, ascites, and pleural effusions.

Hypothyroidism

Hypothyroidism can occasionally cause pleural effusions.

These may be transudative or sometimes borderline/exudative depending on the mechanism, so it is not as classically transudative as heart failure or cirrhosis.

3. Exudative Pleural Effusion

An exudate results from local pleural disease, usually because of increased vascular permeability, inflammation, impaired lymphatic drainage, or direct pleural involvement.

Malignancy

Malignant pleural effusion is a common cause of an exudate.

It may occur with lung cancer, breast cancer, lymphoma, mesothelioma, and other metastatic malignancies. The fluid is often recurrent and may be haemorrhagic.

Parapneumonic Effusion

A parapneumonic effusion develops in association with bacterial pneumonia.

It may be uncomplicated or progress to a complicated parapneumonic effusion or empyema, especially when pleural fluid becomes infected.

Tuberculosis

Tuberculous pleuritis typically causes an exudative effusion.

The fluid is usually lymphocyte-predominant and may have a low glucose concentration.

Subphrenic Abscess

A subphrenic abscess can irritate the adjacent diaphragm and pleura, causing a reactive exudative pleural effusion.

Pulmonary Embolism

Pulmonary embolism can cause a small exudative effusion, especially when pulmonary infarction occurs.

The fluid may be blood-stained.

Pancreatitis

Pancreatitis can cause an exudative pleural effusion, usually through inflammatory spread or a pancreaticopleural fistula.

A clue is a markedly elevated pleural fluid amylase.

Rheumatoid Arthritis

Rheumatoid pleuritis can produce an exudative effusion, often with very low pleural fluid glucose.

The pleural fluid may also have a low pH and high LDH.

Systemic Lupus Erythematosus

SLE can cause pleuritis with an exudative pleural effusion.

This is often associated with other manifestations of active systemic lupus.

4. Low Pleural Fluid Glucose

A reduced pleural fluid glucose concentration suggests that glucose is being consumed by inflammatory cells, bacteria, or metabolically active tissue, or that transport across the pleura is impaired.

Important causes include rheumatoid pleuritis, tuberculosis, malignancy, and empyema.

Rheumatoid Arthritis

Rheumatoid effusions can produce very low glucose levels, sometimes approaching zero.

This is one of the classic laboratory clues to rheumatoid pleuritis.

Tuberculosis

Tuberculous pleural effusions may also have low pleural glucose, particularly in more intense or chronic pleural inflammation.

Malignancy

Malignant effusions can have reduced glucose because of high metabolic activity within the pleural space and impaired glucose transport.

Empyema

In empyema, bacteria and neutrophils consume glucose rapidly, so pleural fluid glucose may become very low.

Empyema is also typically associated with low pH and high LDH.

Key Clinical Pattern

Think of transudates as being caused mainly by systemic pressure or protein problems, especially heart failure, cirrhosis, hypoalbuminaemia, and nephrotic syndrome.

Think of exudates as being caused by local pleural inflammation or infiltration, especially malignancy, pneumonia, TB, pulmonary embolism, pancreatitis, RA, and SLE.

For classification, remember Light’s criteria, and for a particularly low pleural fluid glucose, remember RA, TB, malignancy, and empyema.

Medicine – Bronchiectasis

Bronchiectasis is a chronic respiratory disorder characterised by permanent and abnormal dilatation of the bronchi caused by destruction of the muscular and elastic components of the bronchial walls. Impaired mucus clearance leads to retention of secretions, recurrent infection, and persistent airway inflammation, creating a cycle of further airway damage.

Pulmonary function often demonstrates an obstructive pattern because dilated and damaged airways become narrowed or blocked by retained secretions. However, restrictive or mixed abnormalities can occur when there is extensive associated lung disease.

1. Pathophysiology

Bronchiectasis develops when repeated or severe airway injury damages the bronchial wall and interferes with normal mucociliary clearance.

Secretions accumulate within the affected airways, providing an environment in which bacteria can persist. Recurrent infection causes further inflammation and tissue destruction, resulting in progressively abnormal bronchial dilatation.

This produces a characteristic cycle of:

Impaired mucus clearance → infection → inflammation → bronchial damage → further mucus retention.

Causes of Bronchiectasis

The underlying causes can broadly be divided into congenital or inherited disorders and acquired conditions. In a significant proportion of patients, however, no definite cause is identified.

2. Congenital and Inherited Causes

Selective IgA Deficiency

Selective IgA deficiency can predispose to recurrent respiratory tract infections because IgA plays an important role in protecting mucosal surfaces.

Repeated bacterial infections can eventually damage the bronchial walls and lead to bronchiectasis.

Primary Ciliary Dyskinesia

Primary ciliary dyskinesia is an inherited disorder in which respiratory cilia have abnormal structure or function.

Defective ciliary movement prevents effective removal of mucus and inhaled microorganisms from the respiratory tract. Patients therefore develop recurrent sinus infections, otitis media, chronic productive cough, and bronchiectasis.

Kartagener Syndrome

Kartagener syndrome is a particular phenotype of primary ciliary dyskinesia classically characterised by:

Bronchiectasis + chronic sinusitis + situs inversus.

Situs inversus may include dextrocardia, in which the heart lies predominantly on the right side of the chest.

Male infertility is common because sperm flagella depend on structures similar to respiratory cilia. Female fertility may also be reduced because abnormal ciliary function can interfere with transport through the fallopian tubes.

X-Linked Agammaglobulinaemia

X-linked agammaglobulinaemia, historically called X-linked hypogammaglobulinaemia, causes severe impairment of antibody production.

Affected patients develop recurrent bacterial respiratory infections from childhood. Without adequate treatment, repeated infection can cause permanent airway damage and bronchiectasis.

3. Acquired Causes

Previous Severe Childhood Infection

Severe respiratory infections during childhood can produce permanent bronchial damage.

Classically associated infections include severe bacterial pneumonia, pertussis, and measles, particularly when complicated by significant lower respiratory tract disease.

This form of post-infectious bronchiectasis has become less common in populations with widespread vaccination and improved treatment of childhood infections.

Previous Tuberculosis

Pulmonary tuberculosis can cause substantial destruction and fibrosis of lung tissue.

Following healing, affected areas may develop traction bronchiectasis, particularly in regions of significant pulmonary scarring.

Allergic Bronchopulmonary Aspergillosis

Allergic bronchopulmonary aspergillosis (ABPA) is a hypersensitivity reaction to Aspergillus, occurring mainly in patients with asthma or cystic fibrosis.

Repeated allergic inflammation and mucus plugging can damage the airways and characteristically produce central bronchiectasis.

Bronchial Obstruction

Bronchiectasis may develop distal to an obstructed bronchus because mucus cannot drain normally from the affected segment of lung.

Causes of obstruction include an inhaled foreign body, endobronchial tumour, or other obstructing lesion.

Localised bronchiectasis confined to one particular lobe or segment should therefore raise suspicion of a focal bronchial obstruction.

Pulmonary Fibrosis

Pulmonary fibrosis can distort and pull open the bronchi as the surrounding lung tissue contracts.

This produces traction bronchiectasis, which is commonly seen on high-resolution CT in fibrotic interstitial lung diseases such as idiopathic pulmonary fibrosis and systemic sclerosis-associated ILD.

Cystic Fibrosis

An important additional inherited cause is cystic fibrosis.

Abnormally thick airway secretions impair mucociliary clearance, resulting in recurrent bacterial infection and progressive bronchial destruction. Bronchiectasis is therefore a major pulmonary manifestation of CF.

Idiopathic Bronchiectasis

Despite appropriate investigation, no underlying cause can be identified in some patients.

This is referred to as idiopathic bronchiectasis.

Clinical Features

4. Chronic Productive Cough

The classic symptom is a chronic productive cough, often producing large quantities of mucopurulent or purulent sputum.

Sputum production may increase substantially during infective exacerbations and may be accompanied by fever, worsening cough, and increasing breathlessness.

5. Exertional Breathlessness

Exertional dyspnoea can occur because of airflow obstruction, mucus plugging, recurrent infection, and progressive loss of functioning lung tissue.

Breathlessness tends to become more prominent when disease is extensive or advanced.

6. Haemoptysis

An important additional feature is haemoptysis.

Chronically inflamed airways develop enlarged and fragile bronchial blood vessels that can bleed. Haemoptysis may range from small streaks of blood in the sputum to potentially life-threatening massive bleeding.

7. Cyanosis

Cyanosis is generally a feature of severe or advanced disease and reflects significant impairment of pulmonary gas exchange.

Patients with advanced bronchiectasis may eventually develop chronic respiratory failure.

8. Finger Clubbing

Digital clubbing can occur in bronchiectasis, particularly when the disease is extensive and associated with chronic suppurative infection.

However, clubbing is not present in every patient.

9. Inspiratory Crepitations

Auscultation commonly reveals coarse inspiratory crackles, particularly over the affected areas.

These may be heard during early or mid-inspiration and can sometimes change following coughing as retained airway secretions move.

Wheezing and rhonchi may also occur when significant airflow obstruction is present.

Diagnosis

10. Chest Radiograph

A chest radiograph may demonstrate thickened bronchial walls, parallel linear or “tram-track” shadows, and ring shadows representing dilated bronchi viewed end-on.

However, a normal chest radiograph does not exclude bronchiectasis, particularly when disease is relatively mild.

11. Pulmonary Function Tests

Spirometry commonly demonstrates an obstructive ventilatory defect, with a reduced FEV₁ and FEV₁/FVC ratio.

A restrictive or mixed pattern can occur when there is extensive bronchiectasis or associated pulmonary fibrosis.

12. High-Resolution CT

High-resolution CT (HRCT) of the chest is the key investigation for confirming bronchiectasis.

Characteristic findings include bronchial dilatation, failure of the bronchi to taper normally, and visible airways close to the pleural surface.

A classic CT sign is the “signet-ring sign,” in which a dilated bronchus has a larger diameter than its accompanying pulmonary artery.

HRCT can also demonstrate mucus plugging, bronchial wall thickening, and the anatomical distribution of disease, which may provide clues to the underlying cause.

Key Clinical Pattern

Think of bronchiectasis in a patient with chronic productive cough, recurrent chest infections, purulent sputum, haemoptysis, coarse inspiratory crackles, and sometimes finger clubbing.

Important causes include previous severe infection, primary ciliary dyskinesia/Kartagener syndrome, immunodeficiency, cystic fibrosis, ABPA, previous TB, bronchial obstruction, and pulmonary fibrosis.

The investigation of choice for confirming the diagnosis is high-resolution CT, which demonstrates permanently dilated, non-tapering bronchi, often with the characteristic signet-ring appearance.

Medicine – Cystic Fibrosis

Cystic fibrosis (CF) is a chronic, inherited multisystem disorder caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The abnormal CFTR protein disrupts chloride and bicarbonate transport across epithelial surfaces, producing dehydrated, abnormally thick secretions. The respiratory and gastrointestinal systems are particularly affected, although CF can also cause diabetes, infertility, osteoporosis, and other complications.

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1. Autosomal Recessive Inheritance

Cystic fibrosis is inherited as an autosomal recessive disorder. An affected individual therefore inherits a disease-causing CFTR variant from each parent.

People with only one pathogenic variant are generally healthy carriers.

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2. Carrier Frequency

In populations of Northern European ancestry, approximately 1 in 25 people has traditionally been quoted as carrying a CFTR disease-causing variant.

Carrier frequency varies substantially between different ethnic and geographic populations.

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3. Incidence

Older teaching commonly gives an incidence of approximately 1 in 2,000–2,500 live births in White populations.

The incidence varies by population and has also changed with widespread carrier screening, prenatal testing, and demographic changes.

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4. CFTR Gene

The CFTR gene is located on the long arm of chromosome 7 and encodes the cystic fibrosis transmembrane conductance regulator protein.

CFTR functions primarily as an epithelial chloride and bicarbonate ion channel and also influences the activity of other ion channels.

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5. CFTR Mutations

More than 2,000 CFTR variants have now been identified, although not all cause cystic fibrosis.

The most common disease-causing variant is F508del (ΔF508), which results from deletion of three DNA bases and consequently loss of a phenylalanine residue at position 508 of the CFTR protein.

F508del causes abnormal protein folding and processing, so relatively little functional CFTR reaches the epithelial cell surface.

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6. Abnormal Chloride and Water Transport

Defective CFTR function disrupts the movement of chloride, bicarbonate, sodium, and water across epithelial surfaces.

In the respiratory tract, abnormal ion transport causes dehydration of airway secretions. The resulting mucus becomes thick and difficult to clear, impairing normal mucociliary clearance.

This promotes mucus plugging, chronic bacterial infection, inflammation, and progressive structural damage to the airways.

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Diagnosis

7. Sweat Chloride Test

The sweat chloride test remains an important diagnostic investigation because CFTR dysfunction causes abnormally high concentrations of chloride in sweat.

A sweat chloride concentration of ≥60 mmol/L is consistent with cystic fibrosis in an appropriate clinical setting, usually requiring confirmation according to diagnostic protocols.

Values below this threshold require interpretation according to age, symptoms, newborn screening results, and CFTR genetic testing.

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Why Is Sweat Salty?

In normal sweat ducts, CFTR helps reabsorb chloride, with sodium following.

In cystic fibrosis, defective CFTR reduces chloride reabsorption, leaving increased amounts of chloride and sodium in sweat. This explains the characteristically salty sweat of affected patients.

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8. Life Expectancy

The prognosis of cystic fibrosis has improved dramatically.

Older sources described life expectancy as just over 40 years, but this is now outdated in many countries. Improvements in multidisciplinary care, nutritional support, antimicrobial treatment, and particularly CFTR modulator therapy have substantially increased expected survival.

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Respiratory Manifestations

9. Small-Airway Obstruction and Bronchiectasis

Abnormally thick mucus obstructs the small airways and interferes with mucociliary clearance.

Persistent mucus retention promotes recurrent infection and chronic neutrophilic inflammation. Repeated cycles of obstruction → infection → inflammation → airway damage eventually produce bronchiectasis.

Patients commonly develop chronic cough, sputum production, recurrent respiratory infections, breathlessness, and progressive deterioration in pulmonary function.

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10. Respiratory Infection and Colonisation

Patients with CF are susceptible to chronic and recurrent infection with characteristic respiratory organisms.

Important organisms include Staphylococcus aureus, Haemophilus influenzae, Pseudomonas aeruginosa, and Burkholderia cepacia complex.

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Pseudomonas aeruginosa

Pseudomonas aeruginosa becomes particularly important as patients grow older.

Chronic colonisation can produce progressive airway inflammation and declining lung function. The organism may develop a mucoid phenotype, allowing it to persist within the abnormal airway environment and making eradication increasingly difficult.

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Burkholderia cepacia Complex

Burkholderia cepacia complex is especially important because some strains can cause severe respiratory deterioration and are difficult to treat because of antimicrobial resistance.

Cross-infection between patients with CF is also an important infection-control concern.

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11. Treatment of Respiratory Disease

Pulmonary exacerbations are treated with appropriate antibiotics, guided where possible by respiratory cultures and previous microbiological results.

Some patients receive long-term or inhaled antimicrobial therapy to suppress chronic infection.

Management also includes airway-clearance physiotherapy, exercise, mucolytic therapies, and other treatments designed to improve mucus clearance.

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CFTR Modulator Therapy

A major development in modern treatment is the use of CFTR modulators, which target the underlying abnormal CFTR protein rather than simply treating its consequences.

Different combinations are used according to the patient’s specific CFTR genotype, and highly effective modulator therapy has substantially improved lung function and other outcomes in many eligible patients.

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Gastrointestinal Manifestations

12. Pancreatic Insufficiency

Exocrine pancreatic insufficiency occurs in the majority of patients with classic CF.

Thick secretions obstruct the pancreatic ducts, resulting in progressive pancreatic damage and inadequate delivery of digestive enzymes into the intestine.

This causes fat and protein malabsorption, steatorrhoea, poor weight gain, and deficiencies of fat-soluble vitamins A, D, E, and K.

Treatment includes pancreatic enzyme replacement therapy and nutritional supplementation.

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13. Meconium Ileus

Meconium ileus is an important neonatal presentation of cystic fibrosis.

Abnormally thick intestinal contents obstruct the terminal ileum, producing abdominal distension, failure to pass meconium, and intestinal obstruction shortly after birth.

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Distal Intestinal Obstruction Syndrome

Older children and adults with CF can develop distal intestinal obstruction syndrome (DIOS).

Thick intestinal material accumulates, particularly around the terminal ileum and caecum, producing abdominal pain, distension, and partial or complete intestinal obstruction.

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14. Liver Disease

Abnormal CFTR function can produce thickened bile and obstruction of small intrahepatic bile ducts.

Some patients consequently develop CF-associated hepatobiliary disease, which can include focal biliary fibrosis, multilobular cirrhosis, and portal hypertension.

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15. Gallstones

Gallstones occur more frequently in people with CF.

Altered bile composition and gallbladder dysfunction contribute to their development.

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16. Pancreatitis

Recurrent acute or chronic pancreatitis can occur in some individuals with CF, particularly those who retain a degree of pancreatic exocrine function.

Interestingly, patients with severe pancreatic insufficiency may be less likely to develop pancreatitis because extensive pancreatic destruction has already occurred.

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Other Manifestations

17. Cystic Fibrosis-Related Diabetes

Cystic fibrosis-related diabetes (CFRD) becomes increasingly common with age.

Progressive pancreatic damage reduces insulin secretion, while illness-related insulin resistance may contribute. CFRD has features of both type 1 and type 2 diabetes but represents a distinct form of diabetes associated with CF.

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18. Pneumothorax

Advanced bronchiectasis and structural lung disease can predispose patients to spontaneous pneumothorax.

This may present with sudden worsening of breathlessness and pleuritic chest pain and can be particularly serious in patients who already have significantly reduced pulmonary reserve.

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19. Male Infertility

Almost all men with classic cystic fibrosis are infertile, usually because of congenital bilateral absence or severe abnormality of the vas deferens.

Importantly, spermatogenesis may remain intact, so biological fatherhood may sometimes be possible using assisted reproductive techniques.

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20. Female Reproductive Effects

Women with CF are generally capable of becoming pregnant, although fertility may be reduced.

Abnormally thick cervical mucus, nutritional status, and severity of chronic illness can contribute to reduced fertility.

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21. Osteoporosis

Patients with CF have an increased risk of reduced bone mineral density and osteoporosis.

Contributing factors include chronic inflammation, malabsorption of vitamin D, poor nutritional status, reduced physical activity, delayed puberty, and exposure to systemic corticosteroids in some patients.

This increases the risk of vertebral and other fractures.

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Key Clinical Pattern

Think of cystic fibrosis as an autosomal recessive CFTR disorder causing abnormal epithelial ion and water transport and therefore thick, dehydrated secretions.

The classic pattern is chronic/recurrent respiratory infection + bronchiectasis + pancreatic insufficiency and malabsorption + high sweat chloride.

Important organisms include S. aureus, H. influenzae, P. aeruginosa, and B. cepacia complex, while important extrapulmonary complications include meconium ileus/DIOS, CF-related diabetes, hepatobiliary disease, male infertility, and osteoporosis.

Modern CFTR modulator therapy has transformed the outlook for many patients, making the older life-expectancy figures in traditional notes increasingly outdated.

Medicine – Lung Cancer

Lung cancer is one of the most important causes of cancer-related morbidity and mortality. Most cases are strongly associated with tobacco smoking, although occupational exposures, environmental carcinogens, and pre-existing lung disease also contribute. Lung cancers are broadly divided into non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC) because their biological behaviour, staging, treatment, and prognosis differ substantially.

1. Causes and Risk Factors

Cigarette Smoking

Cigarette smoking is the major preventable cause of lung cancer and accounts for the large majority of cases. Risk increases with the duration and intensity of smoking exposure and decreases progressively after smoking cessation.

Older sources sometimes quote smoking as causing approximately 95% of cases, but modern estimates are generally lower and vary by population, sex, and tumour subtype.

Occupational Exposure

Several occupational carcinogens increase the risk of lung cancer. An important example is asbestos exposure, particularly in construction, shipbuilding, insulation work, and other historically exposed industries.

Smoking and asbestos exposure have a synergistic effect, producing a substantially greater risk of lung cancer when both are present.

Environmental Exposure

Environmental factors include passive tobacco smoke and air pollution. Other important environmental or occupational carcinogens include radon, silica, arsenic, chromium, nickel, and diesel exhaust.

Pulmonary Fibrosis

Lung cancer occurs more frequently in patients with certain forms of pulmonary fibrosis, including idiopathic pulmonary fibrosis.

Chronic epithelial injury, inflammation, and abnormal tissue repair are thought to contribute to malignant transformation.

2. Histological Types

Lung cancers are divided into two major categories:

Non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC).

The percentages in older notes have changed considerably over time. In particular, adenocarcinoma is now the most common histological subtype of lung cancer in many populations, rather than squamous cell carcinoma.

Non-Small-Cell Lung Cancer

NSCLC accounts for approximately 85% of lung cancers and includes adenocarcinoma, squamous cell carcinoma, and large-cell carcinoma.

Adenocarcinoma

Adenocarcinoma is now the most common form of lung cancer.

It frequently develops peripherally within the lung and is also the most common major histological subtype encountered in people who have never smoked, although smoking remains an important risk factor.

Modern classification incorporates several adenocarcinoma growth patterns; the older term bronchoalveolar carcinoma has largely been replaced by more specific pathological categories such as adenocarcinoma in situ and lepidic-predominant adenocarcinoma.

Squamous Cell Carcinoma

Squamous cell carcinoma is strongly associated with cigarette smoking and classically arises in the central or proximal airways.

These tumours may undergo central necrosis and cavitation. Squamous carcinoma is also particularly associated with secretion of parathyroid hormone-related peptide (PTHrP), producing paraneoplastic hypercalcaemia.

Large-Cell Carcinoma

Large-cell carcinoma is a poorly differentiated form of NSCLC diagnosed when the tumour lacks the characteristic features of adenocarcinoma, squamous carcinoma, or another defined subtype.

It can occur in either central or peripheral regions of the lung and tends to behave aggressively.

3. Small-Cell Lung Cancer

Small-cell lung cancer accounts for roughly 10–15% of lung cancers and has an exceptionally strong association with cigarette smoking.

It commonly arises centrally, close to the major bronchi, and is characterised by rapid growth, early lymphatic involvement, and early distant metastasis.

Because SCLC is usually already systemic by diagnosis, surgery has only a very limited role. Treatment generally relies on systemic therapy with or without radiotherapy, depending on disease extent and patient factors.

Respiratory Symptoms

4. Cough

A new persistent cough is one of the commonest presentations of lung cancer.

A change in the character or severity of a pre-existing chronic smoker’s cough can also be significant and warrants investigation.

5. Breathlessness

Dyspnoea may result from bronchial obstruction, collapse of part of the lung, pleural effusion, pneumonia distal to an obstructing tumour, lymphatic spread, or extensive tumour burden.

6. Haemoptysis

Haemoptysis is an important warning symptom.

The amount of blood can range from minor streaking of sputum to substantial bleeding. Persistent or unexplained haemoptysis requires investigation, particularly in an older patient or someone with significant smoking exposure.

7. Chest Pain

Chest pain can result from involvement of the pleura, chest wall, ribs, or mediastinal structures.

Persistent or severe pain may indicate locally advanced disease.

Local Complications

8. Pleural Effusion

Lung cancer can produce a pleural effusion through direct pleural involvement, lymphatic obstruction, or other mechanisms.

A malignant pleural effusion generally indicates advanced disease and has major implications for staging and treatment.

9. Superior Vena Cava Obstruction

A centrally located tumour or enlarged mediastinal lymph nodes may compress the superior vena cava (SVC).

Patients may develop facial and neck swelling, distended neck and chest-wall veins, upper-limb swelling, headache, and breathlessness.

SVC obstruction is particularly associated with centrally located thoracic malignancies, including small-cell lung cancer.

10. Recurrent Laryngeal Nerve Palsy

Involvement of the recurrent laryngeal nerve, particularly the left recurrent laryngeal nerve as it passes through the thorax, can produce vocal cord paralysis.

The characteristic clinical presentation is persistent hoarseness.

11. Phrenic Nerve Palsy

Tumour invasion or compression of the phrenic nerve can paralyse the ipsilateral diaphragm.

A chest radiograph may therefore demonstrate an elevated hemidiaphragm.

12. Pericardial Involvement

Direct or metastatic involvement of the pericardium can cause pericarditis or pericardial effusion.

Large malignant pericardial effusions can impair cardiac filling and potentially produce cardiac tamponade.

13. Dysphagia

Dysphagia may develop when a mediastinal tumour or enlarged lymph nodes compress or invade the oesophagus.

This generally suggests significant local or mediastinal disease.

Paraneoplastic and Non-Metastatic Manifestations

Lung cancers can produce systemic manifestations without direct metastatic spread. These paraneoplastic syndromes are particularly characteristic of certain histological subtypes.

14. SIADH

Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is classically associated with small-cell lung cancer.

Excess ADH causes water retention and dilutional hyponatraemia, which may produce confusion, lethargy, seizures, or other neurological manifestations when severe.

15. Ectopic ACTH Production

Small-cell lung cancer can also produce ectopic adrenocorticotropic hormone (ACTH).

This results in Cushing syndrome, potentially causing hypertension, hyperglycaemia, hypokalaemia, muscle weakness, and metabolic alkalosis.

16. Hypercalcaemia

Squamous cell carcinoma is classically associated with hypercalcaemia through secretion of parathyroid hormone-related peptide (PTHrP).

Hypercalcaemia may also result from bone metastases, although this is a metastatic rather than a true paraneoplastic mechanism.

Patients may develop thirst, polyuria, constipation, confusion, weakness, and cardiac rhythm abnormalities.

17. Gynaecomastia

Rare lung cancers can secrete hormones such as human chorionic gonadotropin (hCG), potentially producing gynaecomastia.

Older texts particularly associate this with large-cell carcinoma, although it is an uncommon manifestation.

18. Clubbing

Finger clubbing is particularly associated with non-small-cell lung cancer.

It may occur alone or as part of hypertrophic pulmonary osteoarthropathy.

19. Lambert–Eaton Myasthenic Syndrome

Lambert–Eaton myasthenic syndrome (LEMS) is a characteristic paraneoplastic neurological syndrome associated particularly with small-cell lung cancer.

Autoantibodies interfere with presynaptic voltage-gated calcium channels at the neuromuscular junction, producing proximal muscle weakness, reduced reflexes, and autonomic symptoms.

20. Hypertrophic Pulmonary Osteoarthropathy

Hypertrophic pulmonary osteoarthropathy (HPOA) is associated particularly with lung cancer, most often NSCLC.

It consists of digital clubbing, periostosis of long bones, and painful arthralgia or arthritis.

Patients may complain of painful swollen wrists, ankles, knees, or long bones.

Treatment

21. Surgery

Surgical resection can potentially cure selected patients with early-stage NSCLC.

Procedures may include segmentectomy, lobectomy, or occasionally pneumonectomy. Whether surgery is appropriate depends on TNM stage, tumour location, lymph-node involvement, cardiopulmonary reserve, and overall fitness.

Modern outcomes are substantially better than the historical figures in the supplied notes, particularly for cancers detected at an early stage.

22. Radiotherapy

Radiotherapy may be used with curative intent in selected localised disease when surgery is unsuitable, including stereotactic radiotherapy for some early-stage tumours.

It may also be combined with systemic therapy in locally advanced disease or used palliatively to relieve symptoms such as pain, haemoptysis, or obstruction.

23. Systemic Treatment

Chemotherapy remains important in both NSCLC and SCLC.

Modern NSCLC treatment has expanded considerably beyond conventional chemotherapy. Depending on tumour histology and molecular testing, patients may receive targeted therapy or immunotherapy.

Testing for actionable molecular abnormalities and immune biomarkers is therefore an important part of contemporary management of advanced NSCLC.

Suitability for Surgery

24. Small-Cell Histology

Small-cell lung cancer is generally not treated surgically because of its strong tendency to metastasise early.

Surgery may occasionally be considered in exceptionally early, carefully staged disease, but this represents a small minority of patients.

25. Advanced or Metastatic Disease

Distant metastatic disease generally excludes curative surgical resection of the primary lung tumour.

Extensive mediastinal nodal disease and invasion of unresectable vital structures may also make surgery inappropriate.

26. Malignant Pleural Effusion

A confirmed malignant pleural effusion represents metastatic pleural involvement and generally excludes conventional curative lung resection.

A bloody effusion alone, however, does not automatically prove malignant involvement and requires appropriate investigation.

27. Poor Performance Status and Pulmonary Reserve

Patients must have sufficient general fitness and cardiopulmonary reserve to tolerate lung resection.

Older rules such as an absolute FEV₁ below 1.5 L are no longer used alone to determine operability. Modern assessment uses predicted postoperative lung function, exercise capacity, comorbidities, and the planned extent of resection.

28. Tumour Location

Very central tumours close to the carina or involving major mediastinal structures can make surgical resection technically difficult.

However, the older rule that a tumour less than 1.5 cm from the carina is automatically inoperable is outdated. Modern decisions are based on formal TNM staging, resectability, and multidisciplinary assessment.

Prognosis

29. Small-Cell Lung Cancer

Small-cell lung cancer generally has a poorer prognosis because of its rapid growth and tendency to metastasise early.

Limited-stage disease has a better prognosis than extensive-stage disease, but recurrence after initial treatment remains common.

30. Non-Small-Cell Lung Cancer

The prognosis of NSCLC varies enormously according to stage.

Early localised cancers treated successfully with surgery or stereotactic radiotherapy can have relatively favourable long-term survival, whereas metastatic disease has a much poorer prognosis.

The historical figure of approximately 10% overall five-year survival is therefore outdated. Modern survival has improved because of earlier detection, better staging, improved surgery and radiotherapy, targeted therapies, and immunotherapy.

Key Clinical Pattern

Think of lung cancer in a patient—particularly one with significant smoking exposure—who develops a new or changing cough, haemoptysis, unexplained breathlessness, persistent chest pain, weight loss, or recurrent chest infection.

Remember the classic paraneoplastic associations: small-cell carcinoma → SIADH, ectopic ACTH and Lambert–Eaton syndrome; squamous cell carcinoma → PTHrP-mediated hypercalcaemia; NSCLC → clubbing and hypertrophic pulmonary osteoarthropathy.

The major distinction is between NSCLC, where surgery may be curative in appropriately selected early-stage disease, and SCLC, which usually requires systemic therapy because of its tendency for rapid growth and early metastatic spread.

Medicine – Mesothelioma

Malignant mesothelioma is an aggressive cancer arising from the mesothelial lining of serosal surfaces, most commonly the pleura. Pleural mesothelioma is strongly associated with previous asbestos exposure and typically appears only after a very long latent period.

1. Malignant Tumour of the Pleura

The most common form is malignant pleural mesothelioma, which develops from the mesothelial cells lining the pleural cavity.

The tumour tends to spread diffusely along the pleural surface, causing irregular pleural thickening and encasement of the lung rather than forming a single discrete mass.

2. Association with Asbestos

A large proportion of pleural mesothelioma cases are related to previous asbestos exposure.

Older teaching often quotes a figure of about 85%, although the exact proportion varies between populations and occupational settings.

Unlike lung cancer, the risk of mesothelioma is not substantially increased by cigarette smoking.

3. Occupational and Secondary Exposure

Mesothelioma has historically been most common in men, reflecting greater occupational exposure to asbestos in industries such as shipbuilding, construction, insulation work, mining, and manufacturing.

However, disease can also occur in people with secondary household exposure. A classic example is a family member who repeatedly handled or washed asbestos-contaminated work clothes.

4. Crocidolite Exposure

Among the major asbestos fibre types, crocidolite, or blue asbestos, has traditionally been regarded as one of the most strongly associated with mesothelioma.

Its long, thin fibres can penetrate deeply into the lungs and pleura and remain within tissues for many years.

5. Long Latency Period

Mesothelioma usually develops only after a prolonged interval following asbestos exposure.

The latency period is commonly 20–50 years or longer, which means patients may present decades after the original occupational or environmental exposure has ended.

6. Clinical Presentation

Patients often present with progressive breathlessness, chest pain, weight loss, fatigue, and recurrent pleural effusions.

The pleural effusion is often unilateral, and the expanding pleural tumour can progressively restrict the affected lung.

7. Imaging

Chest radiography may show unilateral pleural effusion, pleural thickening, and reduced volume of the affected hemithorax.

CT is more useful for demonstrating nodular pleural thickening, pleural masses, involvement of the mediastinal pleura, and encasement of the lung.

8. Diagnosis

Definitive diagnosis usually requires tissue biopsy, often obtained thoracoscopically.

Pleural fluid cytology alone may be insufficient because malignant cells are not always detected in the effusion.

9. Prognosis

Malignant mesothelioma generally has a poor prognosis because it is often advanced at the time of diagnosis and tends to spread extensively along the pleural surface.

Treatment may involve combinations of systemic anticancer therapy, radiotherapy, surgery in highly selected patients, and palliative measures such as management of recurrent pleural effusions.

Key Clinical Pattern

Think of malignant pleural mesothelioma in a patient with a history of asbestos exposure decades earlier who presents with progressive breathlessness, chest pain, weight loss, and a recurrent unilateral pleural effusion.

The key association is asbestos exposure with a very long latency period, and crocidolite (blue asbestos) is classically considered particularly carcinogenic.

Medicine – Interstitial Lung Disease (Pulmonary Fibrosis)

Interstitial lung disease (ILD) refers to a broad group of disorders that affect the pulmonary interstitium and may lead to inflammation, scarring, and progressive pulmonary fibrosis. Patients commonly present with progressive exertional breathlessness, dry cough, fine inspiratory crackles, restrictive lung physiology, and reduced gas transfer.

A useful way to remember the differential diagnosis is by the predominant radiological distribution, particularly whether fibrosis mainly affects the upper or lower lobes.

1. Predominantly Upper-Lobe Disease

Upper-lobe or upper-zone predominance is seen in several granulomatous, occupational, infectious, and inflammatory lung disorders.

Sarcoidosis

Sarcoidosis can produce chronic interstitial lung disease with fibrosis, particularly in longstanding pulmonary disease.

The fibrotic changes tend to involve the upper and mid zones and may be associated with hilar or mediastinal lymphadenopathy, traction bronchiectasis, and architectural distortion.

Tuberculosis

Pulmonary tuberculosis, particularly chronic or previously treated disease, can leave residual upper-lobe fibrosis, volume loss, scarring, and cavitation.

The fibrosis often reflects previous destruction of lung tissue rather than a primary diffuse interstitial fibrotic process.

Pneumoconiosis

Several forms of pneumoconiosis can produce upper-zone nodular and fibrotic changes, especially when exposure has been prolonged.

Coal workers’ pneumoconiosis, for example, may progress from small nodular opacities to progressive massive fibrosis, usually affecting the upper lungs.

Silicosis

Silicosis classically produces multiple small nodules predominantly in the upper lobes.

Advanced disease may result in progressive massive fibrosis with large fibrotic masses and severe distortion of normal lung architecture. Hilar lymph nodes may show characteristic eggshell calcification.

Ankylosing Spondylitis

Ankylosing spondylitis can rarely cause upper-lobe pulmonary fibrosis, usually in longstanding disease.

The fibrosis may be associated with apical scarring, volume loss, and occasionally cavitation. These abnormal upper-lobe spaces can predispose to colonisation by organisms such as Aspergillus.

Allergic Bronchopulmonary Aspergillosis

Allergic bronchopulmonary aspergillosis (ABPA) occurs mainly in patients with asthma or cystic fibrosis and is characterised by hypersensitivity to Aspergillus antigens.

It is more typically associated with central bronchiectasis, mucus plugging, and upper-lobe-predominant infiltrates rather than being a classic primary fibrosing ILD. Chronic or severe disease can nevertheless produce bronchiectatic and fibrotic change.

2. Predominantly Lower-Lobe Disease

Lower-zone or basal predominance is particularly characteristic of several fibrotic and connective tissue-related lung diseases.

Bronchiectasis

Bronchiectasis itself is primarily an airway disorder rather than a true interstitial lung disease.

However, chronic lower-lobe bronchiectasis may produce scarring and fibrotic change around damaged airways, especially when associated with recurrent infection.

Asbestosis

Asbestosis is a diffuse interstitial pulmonary fibrosis caused by significant asbestos exposure.

Fibrosis predominantly affects the lower lobes and subpleural regions. Patients may have dry cough, exertional breathlessness, bibasal inspiratory crackles, finger clubbing, restrictive lung function, and reduced gas transfer.

Usual Interstitial Pneumonia

Usual interstitial pneumonia (UIP) is the characteristic radiological and histological pattern associated with idiopathic pulmonary fibrosis when no secondary cause is identified.

It predominantly affects the subpleural and basal regions and is characterised by reticulation, traction bronchiectasis, and honeycombing.

Rheumatoid Arthritis

Rheumatoid arthritis can cause interstitial lung disease, and the UIP pattern is common.

Patients may develop progressive dry cough and exertional breathlessness with bibasal fibrotic changes on imaging. RA can also cause pleural disease, pulmonary nodules, and bronchiectasis.

Systemic Sclerosis

Systemic sclerosis is strongly associated with interstitial lung disease, typically with a lower-lobe and peripheral predominance.

The most common imaging pattern is nonspecific interstitial pneumonia (NSIP), although UIP can also occur. Pulmonary arterial hypertension is another major pulmonary complication of systemic sclerosis.

3. Drug- and Treatment-Induced Interstitial Lung Disease

Several medications and therapeutic interventions can cause inflammatory pneumonitis, pulmonary fibrosis, or both.

Amiodarone

Amiodarone can cause pulmonary toxicity ranging from mild pneumonitis to severe interstitial fibrosis.

Patients may develop progressive dry cough, dyspnoea, diffuse pulmonary infiltrates, restrictive lung function, and impaired gas transfer.

Methotrexate

Methotrexate can cause drug-induced pneumonitis, often presenting with dry cough, fever, breathlessness, and diffuse infiltrates.

This is usually an inflammatory hypersensitivity-type reaction rather than slowly progressive dose-related fibrosis, although distinguishing drug toxicity from underlying rheumatological lung disease can sometimes be difficult.

Nitrofurantoin

Nitrofurantoin can cause both acute and chronic pulmonary reactions.

Acute disease may resemble hypersensitivity pneumonitis, while prolonged exposure can lead to chronic interstitial inflammation and pulmonary fibrosis.

Bleomycin

Bleomycin is a well-known cause of dose-related pulmonary toxicity.

It can produce interstitial pneumonitis followed by progressive pulmonary fibrosis, and the risk increases with greater cumulative exposure and certain additional risk factors.

Radiotherapy

Thoracic radiotherapy can produce lung injury in two main stages.

An earlier radiation pneumonitis may develop within months of treatment, followed later by permanent radiation fibrosis. The abnormalities often correspond geographically to the irradiated portion of lung.

Key Clinical Pattern

For exam purposes, a useful distribution is:

Upper-lobe predominant: sarcoidosis, TB-related scarring, pneumoconiosis, silicosis, ankylosing spondylitis, and chronic ABPA-related change.

Lower-lobe predominant: asbestosis, UIP/IPF, rheumatoid arthritis-associated ILD, and systemic sclerosis-associated ILD.

Important causes of drug- or treatment-induced ILD include amiodarone, methotrexate, nitrofurantoin, bleomycin, and thoracic radiotherapy.

A useful correction is that bronchiectasis and ABPA are primarily airway diseases rather than classic interstitial lung diseases, although both may produce associated fibrosis in chronic disease.

Medicine – Usual Interstitial Pneumonia (UIP) / Cryptogenic Fibrosing Alveolitis

Usual interstitial pneumonia (UIP) is a characteristic pattern of chronic interstitial lung injury associated with progressive pulmonary fibrosis. The older term cryptogenic fibrosing alveolitis (CFA) was historically used for what is now usually called idiopathic pulmonary fibrosis (IPF) when no underlying cause is identified.

UIP is defined mainly by its radiological and histopathological pattern, whereas IPF is the clinical diagnosis made when that UIP pattern occurs without another identifiable cause.

1. Pathology

UIP is characterised by patchy interstitial fibrosis affecting the lung parenchyma, particularly in the subpleural and basal regions.

A key pathological feature is temporal heterogeneity, meaning that different areas of the lung show different stages of disease at the same time.

Alternating Areas of Lung Injury

Microscopically, there may be alternating zones of:

Relatively normal lung,

Active fibroblastic change,

Established fibrosis, and

Honeycomb destruction.

This patchwork appearance helps distinguish UIP from some other interstitial lung diseases that produce a more uniform pattern of inflammation or fibrosis.

2. Epidemiology

UIP/IPF is generally more common in older adults and has historically been reported more frequently in men than women.

It is also strongly associated with a history of cigarette smoking, although smoking is not required for the diagnosis.

3. Dry Cough

A persistent dry, non-productive cough is one of the most common presenting symptoms.

The cough is usually chronic and may become troublesome as fibrosis progresses.

4. Progressive Breathlessness

Patients commonly develop progressive exertional dyspnoea.

Initially, breathlessness may occur only with significant activity, but as lung compliance and gas transfer deteriorate, symptoms may progress to breathlessness during routine activities or even at rest.

5. Finger Clubbing

Digital clubbing is a recognised physical sign in UIP/IPF.

It reflects chronic pulmonary disease and may be present even before very advanced respiratory failure develops.

6. Cyanosis

Cyanosis may occur in advanced disease when gas exchange becomes severely impaired.

It usually reflects significant arterial hypoxaemia and therefore tends to be a later clinical feature.

7. Fine Inspiratory Crepitations

A very characteristic examination finding is fine, late-inspiratory bibasal crackles, often described as “Velcro” crackles.

These result from the sudden opening of small fibrotic airways and alveolar units during inspiration.

Diagnosis

8. Pulmonary Function Tests

Pulmonary function testing typically shows a restrictive pattern.

There is usually a reduction in:

Forced vital capacity (FVC) and

Total lung capacity (TLC).

The FEV1/FVC ratio is usually normal or increased, helping distinguish restriction from obstructive airway disease.

9. Reduced Gas Transfer

Gas transfer is commonly impaired.

The DLCO/TLCO is reduced, often significantly, because fibrosis thickens and disrupts the alveolar-capillary interface.

This contributes to exertional oxygen desaturation.

10. Chest Radiograph

The chest radiograph may show bilateral bibasal interstitial or reticular shadowing.

As the disease advances, lung volumes may become reduced and coarse reticular change may become more obvious.

However, chest radiography is less sensitive and less specific than high-resolution CT.

11. High-Resolution CT

High-resolution CT (HRCT) is the key imaging investigation.

A typical UIP pattern includes:

Subpleural and basal predominance,

Reticular abnormalities,

Honeycombing, and

Traction bronchiectasis or bronchiolectasis.

Marked ground-glass change is usually less prominent than the fibrotic reticular and honeycomb abnormalities.

12. Honeycomb Change

Honeycombing refers to clustered, cystic air spaces caused by severe destruction and remodelling of normal lung architecture.

It is a hallmark of advanced fibrosis and strongly supports the diagnosis of UIP when present in the appropriate distribution.

13. Type I Respiratory Failure

Advanced disease may produce type I respiratory failure, characterised by hypoxaemia without primary hypercapnia.

This occurs because severe fibrosis impairs diffusion and creates ventilation-perfusion mismatch.

Carbon dioxide retention is usually a late feature because patients initially compensate by increasing ventilation.

14. Excluding Secondary Causes

Before diagnosing idiopathic pulmonary fibrosis, other causes of a UIP pattern must be excluded.

These include connective tissue disease, occupational or environmental exposure, certain drugs, and chronic hypersensitivity pneumonitis.

Therefore, a careful clinical history and appropriate autoimmune and exposure assessment are essential.

Key Clinical Pattern

Think of UIP/IPF in an older patient with progressive exertional breathlessness, persistent dry cough, finger clubbing, and fine bibasal late-inspiratory “Velcro” crackles.

The typical investigation pattern is restrictive spirometry, reduced gas transfer, bibasal interstitial shadowing, and HRCT showing basal subpleural reticulation, traction bronchiectasis, and honeycombing.

The most important modern distinction is that UIP is the radiological/pathological pattern, while idiopathic pulmonary fibrosis is the clinical disease diagnosed when UIP occurs without an identifiable underlying cause.

Medicine – Extrinsic Allergic Alveolitis (Hypersensitivity Pneumonitis)

Extrinsic allergic alveolitis (EAA), now more commonly called hypersensitivity pneumonitis (HP), is an immune-mediated inflammatory disease of the lung caused by repeated inhalation of certain environmental antigens. These antigens are usually derived from organic dusts, fungi, bacteria such as thermophilic actinomycetes, or animal proteins.

Unlike asthma, the main inflammatory process occurs in the alveoli and pulmonary interstitium rather than primarily in the bronchi, which explains why breathlessness and cough are prominent while wheezing is usually absent.

1. Pathogenesis

EAA develops when a susceptible individual repeatedly inhales an antigen capable of producing an abnormal immune response within the distal airways and alveoli.

Traditionally, the disease has been described as involving a combination of type III immune-complex hypersensitivity and type IV delayed T-cell-mediated hypersensitivity.

Repeated inflammation produces lymphocytic alveolitis and interstitial inflammation. If exposure continues, chronic inflammation may eventually result in permanent pulmonary fibrosis.

2. Immunological Mechanism

Patients exposed to the responsible antigen may develop circulating IgG antibodies, sometimes called precipitating antibodies or precipitins.

These antibodies indicate sensitisation to the antigen but do not necessarily prove that it is causing the patient’s lung disease. Cellular immunity, particularly involving T lymphocytes, is also central to the development of hypersensitivity pneumonitis.

Important Types of Extrinsic Allergic Alveolitis

3. Farmer’s Lung

Farmer’s lung is a classic form of hypersensitivity pneumonitis caused by exposure to microorganisms growing in mouldy hay and other agricultural material.

Traditional organisms associated with farmer’s lung include the thermophilic actinomycetes Saccharopolyspora rectivirgula (formerly Micropolyspora faeni) and Thermoactinomyces species.

Farmers may inhale large quantities of these antigens while handling damp or mouldy hay, particularly in poorly ventilated environments.

4. Bird-Fancier’s Lung

Bird-fancier’s lung occurs following repeated exposure to avian proteins from birds such as pigeons, budgerigars, parrots, and poultry.

Antigens are present in bird droppings, feathers, and feather bloom, and may become airborne as fine particles that are inhaled deeply into the lungs.

Repeated exposure can produce either episodic acute disease or a more insidious chronic form.

5. Malt Worker’s Lung

Malt worker’s lung is an occupational form of hypersensitivity pneumonitis associated with exposure to fungal antigens during the production and handling of malt.

A classic causative organism is Aspergillus clavatus, which may contaminate barley and malt and release airborne fungal spores.

Clinical Features

6. Acute Disease

In acute hypersensitivity pneumonitis, symptoms characteristically develop several hours after significant antigen exposure, traditionally around 4–9 hours later.

Patients may experience fever, chills or flu-like symptoms, dry cough, chest tightness, malaise, and shortness of breath. Fine inspiratory crackles may be heard on examination.

Absence of Wheeze

Wheezing is usually absent, which can help distinguish EAA from allergic asthma.

In asthma, the predominant problem is reversible bronchial obstruction. In EAA, inflammation predominantly involves the alveoli, small airways, and interstitial tissues.

Resolution After Exposure

A mild acute episode may improve considerably within approximately 24–48 hours after removal from the causative antigen.

However, symptoms can recur each time the individual is re-exposed. Repeated episodes should therefore prompt careful investigation of occupational, domestic, and recreational exposures.

7. Chronic Hypersensitivity Pneumonitis

Repeated or continuous antigen exposure can produce chronic hypersensitivity pneumonitis.

Patients may develop gradually progressive exertional dyspnoea, persistent cough, fatigue, exercise limitation, and weight loss rather than obvious attacks occurring after exposure.

Longstanding inflammation can lead to irreversible pulmonary fibrosis, architectural distortion, traction bronchiectasis, and eventually chronic respiratory impairment.

Diagnosis

8. Chest Imaging

The chest radiograph may be normal, particularly in mild or early disease.

When abnormal, it may demonstrate diffuse or patchy hazy infiltrates and small nodular opacities.

High-resolution CT (HRCT) is considerably more sensitive and may demonstrate ground-glass opacities, centrilobular nodules, mosaic attenuation, air trapping, and—in chronic fibrotic disease—features of pulmonary fibrosis.

9. Pulmonary Function Tests

Pulmonary function testing commonly demonstrates a restrictive ventilatory defect, particularly when significant interstitial disease is present.

Gas transfer may also be impaired, with a reduced DLCO/TLCO. Some patients, particularly those with prominent small-airway involvement, can demonstrate obstructive or mixed abnormalities.

10. Serum Precipitins

Measurement of serum antigen-specific IgG antibodies, traditionally called serum precipitins, can help demonstrate previous exposure and sensitisation to a suspected antigen.

However, a positive result does not prove active hypersensitivity pneumonitis, because healthy exposed individuals may also develop these antibodies. Similarly, a negative test does not completely exclude the disease.

11. Eosinophilia

Peripheral blood eosinophilia is not a typical feature of EAA.

This is useful when distinguishing hypersensitivity pneumonitis from disorders characterised by prominent eosinophilic inflammation, such as eosinophilic pneumonia or eosinophilic granulomatosis with polyangiitis.

12. Bronchoalveolar Lavage

Bronchoalveolar lavage (BAL) commonly demonstrates an increased proportion of lymphocytes, reflecting the lymphocyte-predominant inflammatory response occurring within the lungs.

Older descriptions emphasise a normal or reduced CD4:CD8 ratio. Although this may occur, the CD4:CD8 ratio is variable and is not sufficiently reliable to diagnose or exclude hypersensitivity pneumonitis.

Treatment

13. Avoidance of the Precipitating Antigen

The most important aspect of treatment is identifying and avoiding the responsible antigen.

This may involve modifying working practices, improving ventilation, using appropriate respiratory protection, removing contaminated material, or—in some cases—completely avoiding the occupational or environmental exposure.

Early antigen avoidance can prevent recurrent attacks and reduce the risk of progression to irreversible fibrosis.

14. Corticosteroids

Systemic corticosteroids may be used in patients with significant acute or subacute disease to reduce pulmonary inflammation and accelerate symptomatic improvement.

Steroids do not replace antigen avoidance, which remains the cornerstone of management. Treatment of chronic fibrotic hypersensitivity pneumonitis is more complex because established fibrosis may be irreversible.

Key Clinical Pattern

Think of extrinsic allergic alveolitis/hypersensitivity pneumonitis when a patient develops fever, dry cough and breathlessness several hours after exposure to an organic antigen, particularly when there is no prominent wheeze.

Classic associations include mouldy hay → farmer’s lung, bird proteins → bird-fancier’s lung, and Aspergillus clavatus → malt worker’s lung.

Diagnosis is supported by the exposure history, HRCT findings, restrictive physiology, antigen-specific IgG and BAL lymphocytosis. The most important treatment is avoidance of the causative antigen, with corticosteroids used when clinically appropriate.

1. Pathogenesis EAA develops when a susceptible individual repeatedly inhales an antigen capable of producing an abnormal immune response within the distal airways and alveoli. Traditionally, the disease has been described as involving a combination of type III immune-complex hypersensitivity and type IV delayed T-cell-mediated hypersensitivity. Repeated inflammation produces lymphocytic alveolitis and interstitial inflammation. If exposure continues, chronic inflammation may eventually result in permanent pulmonary fibrosis. 

2. Immunological Mechanism Patients exposed to the responsible antigen may develop circulating IgG antibodies, sometimes called precipitating antibodies or precipitins. These antibodies indicate sensitisation to the antigen but do not necessarily prove that it is causing the patient’s lung disease. Cellular immunity, particularly involving T lymphocytes, is also central to the development of hypersensitivity pneumonitis. 

Important Types of Extrinsic Allergic Alveolitis 3. Farmer’s Lung Farmer’s lung is a classic form of hypersensitivity pneumonitis caused by exposure to microorganisms growing in mouldy hay and other agricultural material. Traditional organisms associated with farmer’s lung include the thermophilic actinomycetes Saccharopolyspora rectivirgula (formerly Micropolyspora faeni) and Thermoactinomyces species. Farmers may inhale large quantities of these antigens while handling damp or mouldy hay, particularly in poorly ventilated environments. 

4. Bird-Fancier’s Lung Bird-fancier’s lung occurs following repeated exposure to avian proteins from birds such as pigeons, budgerigars, parrots, and poultry. Antigens are present in bird droppings, feathers, and feather bloom, and may become airborne as fine particles that are inhaled deeply into the lungs. Repeated exposure can produce either episodic acute disease or a more insidious chronic form. 

5. Malt Worker’s Lung Malt worker’s lung is an occupational form of hypersensitivity pneumonitis associated with exposure to fungal antigens during the production and handling of malt. A classic causative organism is Aspergillus clavatus, which may contaminate barley and malt and release airborne fungal spores. 

Clinical Features 6. Acute Disease In acute hypersensitivity pneumonitis, symptoms characteristically develop several hours after significant antigen exposure, traditionally around 4–9 hours later. Patients may experience fever, chills or flu-like symptoms, dry cough, chest tightness, malaise, and shortness of breath. Fine inspiratory crackles may be heard on examination. 

Absence of Wheeze Wheezing is usually absent, which can help distinguish EAA from allergic asthma. In asthma, the predominant problem is reversible bronchial obstruction. In EAA, inflammation predominantly involves the alveoli, small airways, and interstitial tissues. 

Resolution After Exposure A mild acute episode may improve considerably within approximately 24–48 hours after removal from the causative antigen. However, symptoms can recur each time the individual is re-exposed. Repeated episodes should therefore prompt careful investigation of occupational, domestic, and recreational exposures. 

7. Chronic Hypersensitivity Pneumonitis Repeated or continuous antigen exposure can produce chronic hypersensitivity pneumonitis. Patients may develop gradually progressive exertional dyspnoea, persistent cough, fatigue, exercise limitation, and weight loss rather than obvious attacks occurring after exposure. Longstanding inflammation can lead to irreversible pulmonary fibrosis, architectural distortion, traction bronchiectasis, and eventually chronic respiratory impairment. 

Diagnosis 8. Chest Imaging The chest radiograph may be normal, particularly in mild or early disease. When abnormal, it may demonstrate diffuse or patchy hazy infiltrates and small nodular opacities. High-resolution CT (HRCT) is considerably more sensitive and may demonstrate ground-glass opacities, centrilobular nodules, mosaic attenuation, air trapping, and—in chronic fibrotic disease—features of pulmonary fibrosis. 

9. Pulmonary Function Tests Pulmonary function testing commonly demonstrates a restrictive ventilatory defect, particularly when significant interstitial disease is present. Gas transfer may also be impaired, with a reduced DLCO/TLCO. Some patients, particularly those with prominent small-airway involvement, can demonstrate obstructive or mixed abnormalities. 

10. Serum Precipitins Measurement of serum antigen-specific IgG antibodies, traditionally called serum precipitins, can help demonstrate previous exposure and sensitisation to a suspected antigen. However, a positive result does not prove active hypersensitivity pneumonitis, because healthy exposed individuals may also develop these antibodies. Similarly, a negative test does not completely exclude the disease. 

11. Eosinophilia Peripheral blood eosinophilia is not a typical feature of EAA. This is useful when distinguishing hypersensitivity pneumonitis from disorders characterised by prominent eosinophilic inflammation, such as eosinophilic pneumonia or eosinophilic granulomatosis with polyangiitis. 

12. Bronchoalveolar Lavage Bronchoalveolar lavage (BAL) commonly demonstrates an increased proportion of lymphocytes, reflecting the lymphocyte-predominant inflammatory response occurring within the lungs. Older descriptions emphasise a normal or reduced CD4:CD8 ratio. Although this may occur, the CD4:CD8 ratio is variable and is not sufficiently reliable to diagnose or exclude hypersensitivity pneumonitis. 

Treatment 13. Avoidance of the Precipitating Antigen The most important aspect of treatment is identifying and avoiding the responsible antigen. This may involve modifying working practices, improving ventilation, using appropriate respiratory protection, removing contaminated material, or—in some cases—completely avoiding the occupational or environmental exposure. Early antigen avoidance can prevent recurrent attacks and reduce the risk of progression to irreversible fibrosis. 

14. Corticosteroids Systemic corticosteroids may be used in patients with significant acute or subacute disease to reduce pulmonary inflammation and accelerate symptomatic improvement. Steroids do not replace antigen avoidance, which remains the cornerstone of management. Treatment of chronic fibrotic hypersensitivity pneumonitis is more complex because established fibrosis may be irreversible. 

Key Clinical Pattern Think of extrinsic allergic alveolitis/hypersensitivity pneumonitis when a patient develops fever, dry cough and breathlessness several hours after exposure to an organic antigen, particularly when there is no prominent wheeze. Classic associations include mouldy hay → farmer’s lung, bird proteins → bird-fancier’s lung, and Aspergillus clavatus → malt worker’s lung. Diagnosis is supported by the exposure history, HRCT findings, restrictive physiology, antigen-specific IgG and BAL lymphocytosis. The most important treatment is avoidance of the causative antigen, with corticosteroids used when clinically appropriate.

Medicine – Occupational Lung Diseases: Coal Workers’ Pneumoconiosis and Silicosis

Occupational lung diseases develop following repeated inhalation of harmful dusts, particles, or chemicals in the workplace. Two important examples are coal workers’ pneumoconiosis (CWP) and silicosis. Both can cause chronic pulmonary inflammation and fibrosis, but they differ in their occupational exposures, radiological distribution, complications, and clinical course.

Coal Workers’ Pneumoconiosis (CWP)

Coal workers’ pneumoconiosis is a chronic occupational lung disease caused by prolonged inhalation of coal mine dust. It occurs predominantly in coal miners and other workers with substantial exposure to respirable coal dust.

Disease severity ranges from relatively mild simple CWP to severe progressive massive fibrosis (PMF).

1. Pathogenesis

During prolonged exposure, very small coal-dust particles are inhaled deeply into the respiratory tract and deposited within the alveoli and respiratory bronchioles.

Alveolar macrophages engulf these particles, but persistent dust accumulation stimulates chronic inflammation and tissue injury. Over time, this can lead to the formation of coal macules, nodules, and pulmonary fibrosis.

2. Simple Coal Workers’ Pneumoconiosis

The early or uncomplicated form is known as simple CWP. Many patients with simple disease have few or no respiratory symptoms.

Chest imaging typically demonstrates multiple small, rounded pulmonary opacities or nodules, often with an upper-lung predominance.

3. Progressive Massive Fibrosis

Simple CWP can progress in some individuals to progressive massive fibrosis (PMF), also called complicated pneumoconiosis.

In PMF, smaller pneumoconiotic nodules merge to form large fibrotic masses, usually in the upper portions of the lungs. This produces significant distortion of normal lung architecture and can result in progressive breathlessness, cough, hypoxaemia, and respiratory impairment.

4. Pulmonary Function Tests

Pulmonary function abnormalities vary according to the extent of disease and the presence of associated airway disease.

A mixed obstructive and restrictive pattern may occur. Obstruction can result from associated chronic airflow limitation, while extensive fibrosis and PMF contribute to restrictive physiology.

5. Occupational Compensation

CWP is a recognised occupational disease, and affected workers may qualify for compensation depending on the diagnostic criteria and legislation of the relevant country.

Older schemes sometimes required characteristic chest radiographic abnormalities for compensation. However, eligibility criteria are jurisdiction-specific and should not be considered a universal medical diagnostic criterion.

Caplan’s Syndrome

Caplan’s syndrome, also known as rheumatoid pneumoconiosis, describes the occurrence of characteristic pulmonary nodules in a patient with rheumatoid arthritis and occupational dust exposure, classically coal dust or silica.

Clinical and Radiological Features

Patients develop multiple, well-defined pulmonary nodules, often appearing relatively rapidly.

The nodules may vary considerably in size and can occasionally undergo central necrosis or cavitation.

Therefore, the classic association to remember is:

Rheumatoid arthritis + pneumoconiosis + multiple pulmonary nodules = Caplan’s syndrome.

Silicosis

Silicosis is an occupational lung disease caused by inhalation of respirable crystalline silica (silicon dioxide). The inhaled particles trigger inflammation and fibrosis within the lungs.

Silicosis may occur as chronic, accelerated, or acute disease, depending largely on the intensity and duration of silica exposure.

1. Occupational Exposure

Workers at risk include those involved in mining, quarrying, stone cutting, tunnelling, foundry work, construction, and abrasive sandblasting.

Modern high-risk exposures can also occur during cutting or fabrication of engineered stone, which may contain a very high concentration of crystalline silica.

2. Acute and Accelerated Disease

Very intense exposure to silica can produce disease much more rapidly than conventional chronic silicosis.

Acute silicosis can develop within months to a few years following extremely heavy exposure and may cause rapidly progressive dyspnoea, dry cough, fatigue, and hypoxaemia.

Accelerated silicosis develops after a shorter period of substantial exposure than chronic silicosis and can progress relatively rapidly to pulmonary fibrosis.

3. Chronic Silicosis

Classic chronic silicosis usually develops after many years of occupational exposure.

The disease is characterised by the formation of multiple small pulmonary nodules, predominantly affecting the upper lobes. These nodules may gradually enlarge and coalesce.

4. Radiological Features

Chest imaging typically demonstrates multiple small, rounded upper-zone nodules.

Hilar and mediastinal lymph nodes may also become enlarged and calcified. A characteristic finding is “eggshell” calcification, in which a thin rim of calcium forms around the periphery of a lymph node.

Advanced silicosis may progress to progressive massive fibrosis, producing large fibrotic upper-lobe masses and severe architectural distortion.

5. Pulmonary Function

Pulmonary function may initially remain relatively preserved. With advanced fibrosis, a restrictive ventilatory defect can develop.

Some patients demonstrate obstructive or mixed abnormalities, particularly when other occupational exposures or smoking-related lung disease coexist.

6. Association with Tuberculosis

An especially important complication of silicosis is an increased susceptibility to tuberculosis.

Silica impairs macrophage function and reduces the ability of the lungs to contain Mycobacterium tuberculosis. Consequently, a patient with silicosis who develops constitutional symptoms, new pulmonary infiltrates, or cavitation should be investigated carefully for active TB.

Key Clinical Differences

Coal workers’ pneumoconiosis results from prolonged coal-dust exposure and produces small pulmonary opacities that may progress to progressive massive fibrosis. The combination of pneumoconiosis, rheumatoid arthritis, and multiple pulmonary nodules is known as Caplan’s syndrome.

Silicosis results from inhalation of crystalline silica, particularly during mining, quarrying, stone cutting, and sandblasting. It characteristically produces upper-lobe nodules, may cause eggshell calcification of hilar lymph nodes, and can progress to massive fibrosis. A particularly important association is the substantially increased risk of tuberculosis.