Medicine – Connective Tissue Disease and the Lung

Connective tissue diseases (CTDs) frequently involve the respiratory system. Pulmonary manifestations may affect the lung parenchyma, pleura, airways, pulmonary vasculature, or respiratory muscles. In some patients, lung disease may become a major cause of morbidity and can occasionally precede the more typical systemic manifestations of the underlying connective tissue disorder.

1. Rheumatoid Arthritis

Rheumatoid arthritis (RA) can produce several different pulmonary manifestations. Lung involvement is particularly important in patients with longstanding or seropositive disease and may involve the lung parenchyma, pleura, or airways.

Pulmonary Nodules

Rheumatoid nodules can develop within the lungs, particularly in patients with severe seropositive RA. They are usually located peripherally and may be single or multiple.

Some rheumatoid nodules undergo central necrosis and cavitation, which can make them difficult to distinguish radiologically from infection, malignancy, or other causes of cavitating pulmonary nodules.

Pulmonary Fibrosis

Interstitial lung disease (ILD) is one of the most important pulmonary complications of RA. Progressive inflammation and fibrosis of the pulmonary interstitium can produce exertional breathlessness, persistent dry cough, and reduced exercise tolerance.

High-resolution CT may demonstrate several patterns, with usual interstitial pneumonia (UIP) and nonspecific interstitial pneumonia being important examples.

Bronchiectasis

Bronchiectasis occurs more frequently in patients with RA than in the general population. Permanent dilatation of the bronchi can result in chronic productive cough, recurrent respiratory infections, and haemoptysis.

Its presence is particularly important when immunosuppressive treatment is being considered because recurrent pulmonary infection may complicate therapy.

Caplan’s Syndrome

Caplan’s syndrome, also known as rheumatoid pneumoconiosis, occurs when rheumatoid arthritis is associated with occupational exposure to mineral dust, classically coal or silica.

Chest imaging typically demonstrates multiple, well-defined pulmonary nodules, which may enlarge or occasionally cavitate.

Pleural Effusion

RA can cause pleuritis with pleural effusion. The effusion is usually exudative and characteristically may have a very low glucose concentration and low pH.

Patients may experience pleuritic chest pain and breathlessness, although some rheumatoid pleural effusions are discovered incidentally.

2. Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) can affect several components of the respiratory system. Although pulmonary fibrosis and shrinking lung syndrome are recognised manifestations, SLE can also cause pleuritis, pleural effusions, acute lupus pneumonitis, and pulmonary haemorrhage.

Pulmonary Fibrosis

Chronic interstitial lung disease and pulmonary fibrosis can occur in SLE, although clinically significant fibrosis is less characteristic than in systemic sclerosis.

Patients may develop progressive exertional dyspnoea, dry cough, restrictive pulmonary function abnormalities, and impaired gas transfer.

Shrinking Lung Syndrome

Shrinking lung syndrome is a rare but distinctive pulmonary complication of SLE. It is characterised by progressive breathlessness, reduced lung volumes, and elevation of the diaphragm without significant interstitial lung disease explaining the restriction.

The mechanism is not completely understood but may involve diaphragmatic dysfunction, pleural inflammation, and abnormalities of respiratory muscle function.

3. Systemic Sclerosis

Systemic sclerosis (scleroderma) has a particularly strong association with pulmonary disease. Lung involvement is clinically important because it is a major contributor to morbidity and mortality.

The two major pulmonary complications to remember are interstitial lung disease and pulmonary arterial hypertension.

Pulmonary Fibrosis

Interstitial lung disease with pulmonary fibrosis is a major manifestation of systemic sclerosis. The most common radiological pattern is nonspecific interstitial pneumonia (NSIP).

Progressive fibrosis causes exertional dyspnoea, dry cough, restrictive lung physiology, and reduced diffusing capacity. High-resolution CT and pulmonary function tests are important for assessment and monitoring.

Bronchiectasis

Bronchiectatic changes may occur in systemic sclerosis, particularly as traction bronchiectasis secondary to pulmonary fibrosis. As fibrotic lung tissue contracts, it pulls the airways open and produces abnormal bronchial dilatation.

This differs from primary bronchiectasis caused mainly by recurrent airway infection.

Pulmonary Arterial Hypertension

An additional important manifestation is pulmonary arterial hypertension (PAH), particularly associated with limited cutaneous systemic sclerosis.

Patients may develop progressive exertional breathlessness, fatigue, syncope, and eventually right-sided heart failure. Pulmonary hypertension can occur independently of significant pulmonary fibrosis and therefore requires specific consideration during follow-up.

Key Clinical Pattern

Rheumatoid arthritis is associated with pulmonary nodules, interstitial fibrosis, bronchiectasis, Caplan’s syndrome, and pleural disease.

SLE can cause interstitial lung disease and shrinking lung syndrome, as well as pleuritis, pneumonitis, and pulmonary haemorrhage.

Systemic sclerosis is particularly associated with interstitial pulmonary fibrosis and pulmonary arterial hypertension, while bronchiectatic changes may develop secondary to fibrosis.