KembaraXtra-Medicine – Methemoglobinemia


Methemoglobinemia is a condition in which the iron molecule within hemoglobin is oxidized from the ferrous (Fe²⁺) state to the ferric (Fe³⁺) state, producing methemoglobin, a form of hemoglobin that is unable to transport oxygen. As a result, the effective oxygen-carrying capacity of blood is reduced, leading to tissue hypoxia and cyanosis at significant levels. Normal methemoglobin levels are ≤1%, and symptoms typically develop when levels exceed 20%. The condition is more severe in patients with coexisting anemia. Methemoglobin causes functional anemia by reducing total oxygen delivery and shifts the hemoglobin–oxygen dissociation curve to the left, impairing oxygen release to tissues. Under normal circumstances, methemoglobin levels are maintained at physiologic ranges by NADH-dependent methemoglobin (cytochrome B5) reductase in red blood cells.


Methemoglobinemia may be congenital or acquired. Congenital forms are usually due to NADH–methemoglobin (cytochrome B5) reductase deficiency, which may be homozygous or heterozygous, or due to abnormal hemoglobins such as hemoglobin M. Acquired methemoglobinemia results from oxidative stress on red blood cells caused by various drugs and chemicals. Some agents act as direct oxidants, such as nitrites, while others cause oxidant injury through N-hydroxylamine metabolites. Onset may be delayed after exposure. Many causative agents also produce Heinz body hemolytic anemia through oxidative damage to red blood cell proteins, particularly in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Therefore, patients diagnosed with methemoglobinemia should also be evaluated for hemolysis. In some cases, methemoglobinemia may serve as a marker for underlying genetic susceptibility, such as heterozygous cytochrome B5 reductase deficiency.


Numerous substances are associated with acquired methemoglobinemia. These include cyanide antidote kits containing amyl or sodium nitrite, nitrates and nitrites (including nitroglycerin via metabolic conversion), nitric oxide, aniline dyes, excessive methylene blue, antiparasitic agents such as dapsone, primaquine, and chloroquine, and local anesthetics including benzocaine, lidocaine, and prilocaine. Other implicated agents include phenazopyridine, phenacetin, nitrofurantoin, sulfonamides, metoclopramide, naphthalene, paraquat, arsine gas, chlorates, and phenolic compounds.


Clinically, methemoglobinemia presents with central cyanosis that does not improve with supplemental oxygen. In nonanemic patients, cyanosis becomes apparent when methemoglobin levels reach approximately 10–15% of total hemoglobin. Additional symptoms include dyspnea, tachypnea, chest pain, dysrhythmias, syncope, and altered mental status, particularly when levels exceed 50%. History should focus on exposure to oxidant agents, timing and amount of ingestion, presence of G6PD deficiency, and comorbid conditions that impair oxygen delivery, such as coronary artery disease. Physical examination typically reveals cyanosis, with particular attention required for neurologic and cardiovascular findings. Signs of hemolytic anemia, such as icterus or dark-colored urine, may also be present.


Diagnostic evaluation requires recognition that pulse oximetry is unreliable in methemoglobinemia. Methemoglobin interferes with pulse oximeter readings, often producing a saturation near 85% regardless of severity, and therefore cannot be used to guide management. Arterial blood gas analysis with co-oximetry is essential to directly measure methemoglobin levels, assess oxygenation, and exclude other dyshemoglobinemias such as carboxyhemoglobinemia. The blood may appear characteristically chocolate brown. Additional investigations include a complete blood count with peripheral smear to evaluate for hemolysis and chest radiography to exclude alternative pulmonary causes of hypoxia.


Initial management focuses on airway, breathing, and circulation stabilization, cardiac monitoring, intravenous fluids for hypotension, administration of supplemental oxygen, and treatment of hypoglycemia or altered mental status as indicated. If recent ingestion is suspected and airway reflexes are intact, activated charcoal may be administered. The source of oxidant stress must be identified and removed. Methylene blue is the treatment of choice for significant methemoglobinemia and is indicated in symptomatic patients with levels above 10–20% or asymptomatic patients with levels above 30%. Transient worsening of pulse oximetry readings after methylene blue administration is expected and does not require intervention. Caution is required in patients with G6PD deficiency, as methylene blue may precipitate hemolysis. Lack of response should prompt consideration of continued exposure or alternative diagnoses such as sulfhemoglobinemia, which does not respond to methylene blue.


In severe or refractory cases, red blood cell transfusion may be required to improve oxygen-carrying capacity, particularly when hemolysis is present. Exchange transfusion may be necessary in neonates and infants. Hyperbaric oxygen therapy can be considered in life-threatening cases when immediately available, as it enhances oxygen delivery independent of hemoglobin. Children and neonates are at higher risk, may develop delayed symptoms after seemingly minor exposures, and often require prolonged observation due to reduced methemoglobin reductase activity.


Hospital admission is indicated for severely symptomatic patients, those requiring repeated doses of methylene blue, or cases associated with prolonged or recurrent methemoglobinemia such as dapsone exposure. Patients may be discharged once methemoglobin levels fall below 20%, are trending downward, and symptoms have resolved in the absence of significant comorbid disease. Toxicology consultation is recommended for significant exposures, and occupational medicine follow-up is appropriate for work-related cases. Key clinical pitfalls include reliance on pulse oximetry instead of arterial blood gas with co-oximetry and delayed administration of methylene blue in symptomatic patients.

KembaraXtra- Medicine – Atrial Flutter


Typical atrial flutter is a stable macroreentrant atrial rhythm that circulates around the tricuspid annulus in the right atrium. The critical component of this circuit is the cavotricuspid isthmus (CTI), the tissue between the inferior vena cava and the tricuspid valve, which is why typical flutter is also referred to as CTI-dependent atrial flutter. Because the circuit is anatomically and physiologically stable, atrial depolarization is regular, usually occurring at a rate of 250–350 beats per minute.


Atypical atrial flutter refers to regular macroreentrant atrial tachyarrhythmias that do not depend on the CTI. These forms often occur after cardiac surgery, in patients with congenital heart disease, or following catheter ablation procedures—particularly left atrial ablation for atrial fibrillation—although they may also occur without an identifiable cause.


Conduction through the atrioventricular (AV) node in atrial flutter often follows predictable ratios. For example, with an atrial rate of 300 beats per minute, 2:1 AV conduction produces a ventricular rate of about 150 beats per minute, while 3:1 and 4:1 conduction produce ventricular rates of approximately 100 and 75 beats per minute, respectively. When AV nodal conduction varies, the ventricular rhythm may appear irregular, although a consistent atrial cycle length is often still present.


Atrial flutter is the second most common sustained atrial tachyarrhythmia after atrial fibrillation, with an estimated 200,000 new cases each year in the United States. Its prevalence increases with age and is about 2.5 times more common in men than in women. It is frequently seen in patients with congestive heart failure, chronic obstructive pulmonary disease, pulmonary embolism, pulmonary hypertension, or in the early postoperative period following open-heart surgery. Importantly, more than half of patients with atrial flutter will develop atrial fibrillation within three years, and more than 80% within five years.


Clinically, atrial flutter may present with palpitations, dizziness, light-headedness, syncope or near syncope, chest pain, dyspnea, or worsening heart failure. Some patients develop thromboembolic complications due to intracardiac thrombus formation. Common etiologic associations include age-related atrial degeneration, rheumatic or congenital heart disease, ventricular dysfunction, mitral valve disease, thyrotoxicosis, pulmonary embolism, obesity, pericarditis, and prior cardiac surgery. Antiarrhythmic therapy for atrial fibrillation may also predispose patients to developing atrial flutter.


Diagnosis is primarily established by electrocardiography. Typical findings include absence of normal P waves and the presence of regular “sawtooth” flutter waves without an isoelectric baseline, most clearly seen in the inferior leads (II, III, and aVF). Atrioventricular conduction is usually 2:1, 3:1, or 4:1 rather than 1:1, unless pre-excitation is present. Holter or event monitoring may be useful for intermittent symptoms or to assess rate control. Echocardiography is recommended in newly diagnosed patients to evaluate for structural heart disease, and transesophageal echocardiography may be required to exclude atrial thrombus before cardioversion. Electrophysiologic studies are used for definitive diagnosis and for catheter ablation therapy.

KembaraXtra-Medicine – Atrial Myxoma


Atrial myxoma is a benign neoplasm of mesenchymal origin and represents the most common primary tumor of the heart. Although histologically benign, atrial myxomas are clinically significant because their size, mobility, and intracardiac location can lead to serious and sometimes life-threatening complications. They are most commonly referred to as cardiac myxomas.


Primary cardiac tumors are extremely rare, with an autopsy prevalence ranging from 0.001% to 0.3%, and metastatic tumors occur far more frequently than primary tumors. Among primary cardiac tumors, myxomas account for 30% to 50% of benign cases. Approximately 65% occur in females. Most cases are sporadic, but 4.5% to 10% are familial, commonly associated with Carney complex. The median age of presentation is about 56 years, although familial cases tend to occur earlier, with an average age of 25 years. Most myxomas arise in the left atrium (about 75%), followed by the right atrium, right ventricle, and left ventricle. They are typically pedunculated and attached to the interatrial septum.


Histopathologically, atrial myxomas are characterized by abundant loose myxoid stroma containing scattered round, polygonal, or stellate cells with dense, irregular nuclei derived from multipotent mesenchymal cells. While benign in classification, myxomas can secrete cytokines and growth factors, contributing to systemic and constitutional symptoms in addition to mechanical complications.


Clinically, patients with atrial myxomas usually present in one of three ways: atrioventricular valve obstruction, systemic embolization, or constitutional symptoms. Obstructive symptoms may mimic mitral or tricuspid valve disease and include dyspnea, orthopnea, paroxysmal nocturnal dyspnea, syncope, dizziness, edema, atrial fibrillation, or rarely sudden death. Symptoms that vary with body position, particularly improvement when recumbent, are suggestive. Systemic embolization occurs in nearly one third of patients and may manifest as stroke, pulmonary embolism, paradoxical embolism, or acute coronary syndrome. Constitutional features such as fever, weight loss, arthralgia, and Raynaud phenomenon are also common, while rare presentations include peripheral neuropathy, vasculitis, or paraneoplastic syndromes. On examination, findings may include murmurs, signs of pulmonary hypertension, a widely split first heart sound, or a characteristic early diastolic “tumor plop.”


Most atrial myxomas are sporadic, but familial cases are commonly associated with Carney complex, an autosomal dominant condition characterized by cardiac and extracardiac myxomas, pigmented skin lesions, endocrine hyperactivity, and other tumors such as schwannomas. Multiple genetic loci and mutations have been identified in this syndrome.


Diagnosis requires a high index of suspicion due to nonspecific symptoms that overlap with many cardiovascular and pulmonary conditions. Laboratory tests may show anemia, thrombocytopenia, elevated inflammatory markers, increased immunoglobulins, or elevated cardiac biomarkers, though these findings are nonspecific. Electrocardiography may reveal atrial enlargement, arrhythmias, or conduction abnormalities. Transthoracic echocardiography is the initial diagnostic test of choice, with approximately 95% sensitivity, while transesophageal echocardiography approaches 100% sensitivity and better defines tumor attachment and mobility. CT and MRI are valuable for delineating tumor size, extension, vascularity, and for distinguishing myxoma from atrial thrombus. Cardiac catheterization may demonstrate neovascularization and is sometimes used to assess for concomitant coronary artery disease before surgery.


The definitive treatment for atrial myxoma is prompt surgical excision, which should not be delayed due to the risk of embolization or sudden death. Postoperatively, arrhythmias or conduction disturbances may occur and are managed accordingly. In rare cases, particularly with recurrent tumors associated with Carney complex, advanced surgical approaches such as cardiac autotransplantation or transplantation may be required.


Prognosis after surgical excision is excellent, with reported survival rates of approximately 95% at three years. However, recurrence can occur in up to 5% of sporadic cases and up to 20% of familial cases, particularly within the first six years. Risk factors for recurrence include familial disease, atypical tumor location, and multicentric tumors. Malignant transformation into atrial myxofibrosarcoma, although rare, should be considered in cases of early recurrence. Untreated atrial myxomas carry a significant risk of sudden death, estimated at up to 15%.


Referral to a cardiologist is recommended for diagnosis and management, and once identified, early consultation with a cardiovascular surgeon is essential. Long-term follow-up with periodic echocardiography is advised to monitor for recurrence, especially in patients with familial disease or Carney complex.

KembaraXtra-Medicine – Autoimmune Hemolytic Anemia


Autoimmune hemolytic anemia (AIHA) is a condition in which autoantibodies and/or complement bind to red blood cells (RBCs), leading to their premature destruction. About half of cases are primary (idiopathic), while the rest are secondary to underlying diseases or drugs. AIHA is commonly categorized into warm antibody–mediated disease (usually IgG, reacting best at 37°C), cold antibody–mediated disease (typically IgM with complement), and drug-induced immune hemolysis.


AIHA is uncommon, with an annual incidence of about 1 to 3 cases per 100,000 people and an estimated mortality around 10%. It is reported more often in women younger than 50 years. Patients most commonly present with fatigue and dyspnea. Pallor and jaundice may be present, and tachycardia with a flow murmur can occur when anemia is significant. Intravascular hemolysis may cause dark urine and back pain. Hepatomegaly or lymphadenopathy suggests a lymphoproliferative disorder or malignancy, while splenomegaly may suggest hypersplenism. The course is often chronic with relapses.


Warm AIHA is usually mediated by IgG antibodies and may be idiopathic or associated with leukemia/lymphoma, thymoma, myeloma, viral infections, babesiosis, and collagen-vascular diseases. Cold AIHA is commonly IgM- and complement-mediated and may be idiopathic or linked to infections, lymphoma, or cold agglutinin disease. Drug-induced AIHA can occur through different immune mechanisms, including antibodies directed against RBC antigens (e.g., methyldopa), antibodies against an RBC–drug complex (hapten type, e.g., penicillin), or immune complex mechanisms (e.g., quinidine).


The differential diagnosis includes non-immune causes of hemolysis such as microangiopathic hemolytic anemia (e.g., TTP/HUS), hypersplenism, prosthetic valve hemolysis, infections, toxins, and inherited causes such as membrane disorders (e.g., hereditary spherocytosis), hemoglobinopathies, and enzyme deficiencies (e.g., G6PD). Chronic lymphocytic leukemia (CLL) can cause a positive direct antiglobulin test (DAT) without true AIHA, so labs and clinical evidence of hemolysis are important.


Evaluation focuses on confirming hemolysis and establishing immune causation. Typical hemolysis findings include reticulocytosis (or reticulocytopenia if marrow suppression is present), low haptoglobin, elevated indirect bilirubin, and elevated LDH. Initial tests include CBC, reticulocyte count, bilirubin/LDH, and a peripheral smear (spherocytes are typical in warm AIHA). The key diagnostic test is the direct antiglobulin test (DAT/Coombs), performed initially with a polyspecific reagent to detect IgG and/or complement on RBCs. A positive DAT supports AIHA: IgG ± C3d suggests warm AIHA, while C3d alone suggests cold AIHA. Additional evaluation may include hepatitis serologies, HIV testing, ANA, urine testing for hemoglobinuria/hemosiderinuria, and imaging (such as CT chest/abdomen/pelvis) if an underlying lymphoproliferative disorder is suspected.


Management includes stopping any offending drug when drug-induced disease is possible. Severe, life-threatening cases may rarely require plasmapheresis or exchange transfusion. Patients with cold antibody AIHA should avoid cold exposure. Warm AIHA is typically treated first with prednisone 1 to 2 mg/kg/day, with tapering after response. Some evidence supports upfront combination therapy with steroids plus rituximab to improve outcomes and durability of response. For relapse or steroid-refractory disease, rituximab is commonly used and has high response rates, with a substantial portion maintaining remission years later. Splenectomy is now usually reserved for cases refractory to both steroids and rituximab, and further options include immunosuppressive agents such as mycophenolate, cyclosporine, cyclophosphamide, IVIG, and sometimes danazol as an adjunct.


Cold AIHA generally responds poorly to corticosteroids, and treating underlying infection or lymphoproliferative disease is important. In primary cold agglutinin disease, rituximab-based regimens (often with bendamustine in fit patients) are commonly used, while rituximab alone may be used in older or frailer patients. IVIG or plasmapheresis can be used temporarily in severe cases while waiting for a durable therapy to work. Complement-directed therapies may be considered in severe disease; sutimlimab (targeting C1s) has been shown to rapidly reduce hemolysis and improve hemoglobin and fatigue in cold agglutinin disease. Splenectomy is generally ineffective in cold AIHA because clearance occurs mainly in the liver.


Prognosis is generally good unless AIHA is driven by a serious underlying condition such as leukemia or myeloma. Hematology referral is recommended for all AIHA cases, and surgical referral may be needed if splenectomy is being considered for refractory warm AIHA.

KembaraXtra-Medicine – Atrioventricular Dissociation


Atrioventricular (AV) dissociation means there is no consistent relationship between atrial activity and ventricular activity—the atria and ventricles are functioning independently. This is an umbrella concept rather than a single diagnosis, because AV dissociation can appear in several different rhythm problems, including slow rhythms (bradycardias), complete heart block, and fast rhythms (tachycardias) such as ventricular tachycardia or situations where an atrial rhythm coexists with an accelerated junctional rhythm or AV nodal reentrant tachycardia.


AV dissociation is sometimes referred to as complete AV block or third-degree AV block, and it is associated with the ICD-10CM code I44.2 (Atrioventricular block, complete). Its overall “prevalence” depends on how common the underlying conditions are that produce AV dissociation, rather than AV dissociation being counted as one separate disease on its own.


Clinical findings can be normal if the rhythm is not causing problems with blood flow. If the right atrium contracts against a closed tricuspid valve during ventricular systole, cannon A waves may be visible in the jugular venous pulse. Symptoms vary depending on the rhythm and the patient’s stability and may include dizziness, palpitations, syncope or presyncope (from reduced cardiac output), fatigue and reduced exercise tolerance, mental status changes, congestive heart failure symptoms, or angina. Some patients may have no symptoms at all.


Causes of AV dissociation include a sinus node that fires too slowly, or a ventricular/junctional pacemaker that is firing inappropriately fast relative to the atria. It can also be iatrogenic, such as from anesthesia, inotrope infusions, ventricular pacing, radiofrequency ablation (for example, slow pathway ablation), or digoxin toxicity. Other contributors include sinus node disease, ischemia, hyperkalemia, and high vagal tone. When AV dissociation occurs due to complete heart block, causes include progressive fibrosis of the His–Purkinje system, medications, and infections such as Lyme disease.


Diagnosis is based on ECG evidence of atrial and ventricular activity that are not linked in a consistent pattern. The differential diagnosis should focus on rhythm disorders that can produce AV dissociation. Importantly, the atrial rate does not have to be faster than the ventricular rate for AV dissociation (that “atrial faster than ventricular” idea fits more specifically with the classic definition of complete heart block). Two related patterns include isorhythmic AV dissociation, where atrial and ventricular rates are similar but dissociated, and interference dissociation, where atrial and ventricular rates are close and occasional conduction may occur.


Workup should be guided by the clinical situation. Routine labs, cardiac biomarkers, and imaging may be needed depending on symptoms and suspected cause, with special attention to electrolytes (especially potassium) and a digoxin level when relevant. If complete heart block is suspected and exposure risk is plausible, Lyme antibody testing should be considered.


Treatment depends first on whether the patient is stable and on whether the rhythm is slow or fast. In bradycardic AV dissociation with symptoms or hemodynamic compromise, a temporary pacemaker is the most reliable immediate therapy. AV nodal blocking agents should be held, and chronotropic medications such as atropine, dopamine, dobutamine, or isoproterenol can be used as temporary measures while preparing for pacing when appropriate. In tachycardic causes such as ventricular tachycardia, unstable patients should receive cardioversion first. Intravenous antiarrhythmics such as amiodarone or lidocaine may be used to suppress the arrhythmia, and definitive management focuses on the underlying cause, such as evaluating ischemia (including coronary angiography if indicated) or electrophysiology study with possible ablation.


All patients with AV dissociation should be referred to a cardiologist for evaluation of the rhythm and its cause. The key reminder is that AV dissociation itself is a sign/pattern—management, prognosis, and disposition are determined by the specific arrhythmia and clinical context producing it.

​Emergency and Acute Medicine – Lymphadenitis
​Basics description
Lymphadenitis refers to inflammation and enlargement of lymph nodes, most commonly as part of a systemic response to infection. Nodes become engorged with lymphocytes and macrophages and may be secondarily involved from infection in a distal extremity, producing painful, tender adenopathy proximally. Acute suppurative lymphadenitis may follow pharyngeal or skin infections and can progress to abscess formation.
Etiology
Lymphadenitis is most frequently caused by bacterial infection. The most common organisms in pyogenic lymphadenitis are Staphylococcus aureus, including community-associated methicillin-resistant S. aureus (CA-MRSA), and group A β-hemolytic Streptococcus. CA-MRSA risk factors include prior MRSA infection, household exposure, military service, incarceration, contact sports, injection drug use, and men who have sex with men. Cervical lymphadenitis usually originates from pharyngeal or periodontal infections and commonly involves streptococci and anaerobes. Axillary lymphadenitis is often caused by group A streptococcus. Nosocomial MRSA should be suspected in patients with recent hospitalization, surgery, dialysis, vascular catheters, recent antibiotic use, or unresponsive infection. In children, acute unilateral cervical suppurative lymphadenitis is most common in those younger than six years and is typically caused by S. aureus, group A streptococcus, or anaerobes.
Diagnosis signs and symptoms
Patients typically present with painful swelling and inflammation of affected lymph nodes, often in association with cellulitis or abscess if the cause is pyogenic. Axillary lymphadenitis may present with fever, axillary pain, and acute lymphedema of the arm or chest and may be associated with ipsilateral pleural effusion. History should include duration of lymphadenopathy, pain, fever, night sweats, weight loss, fatigue, sore throat, cough, occupational and animal exposures, sexual history, drug use, and travel. Physical examination should assess whether lymphadenopathy is localized or generalized, node size, tenderness, overlying skin changes, presence of skin lesions, splenomegaly, and involvement of supraclavicular or scalene nodes, which is always abnormal.
Essential workup
Acute regional lymphadenitis is usually a clinical diagnosis and often part of a broader infectious syndrome such as cellulitis. History and physical examination should focus on identifying an infectious source.
Diagnosis tests and interpretation
Laboratory testing is not always required. A CBC may show leukocytosis with left shift or be normal. Serologic testing for EBV, CMV, HIV, or other pathogens should be guided by clinical suspicion. Ultrasound or CT imaging is indicated when patients fail to improve with therapy or when suppuration is suspected. Percutaneous needle aspiration or surgical drainage should be considered if abscess formation occurs or if there is poor clinical response.
Differential diagnosis
The differential diagnosis includes common infections such as adenovirus, scarlet fever, cat scratch disease, fungal infections, and herpes zoster, as well as unusual infections including sporotrichosis, diphtheria, plague, anthrax, typhoid, rubella, and West Nile virus. Sexually transmitted infections, systemic infections such as HIV, infectious mononucleosis, toxoplasmosis, tuberculosis, hepatitis, and dengue should be considered. Noninfectious causes include drug reactions, malignancy, rheumatologic disorders, and pediatric-specific conditions such as Kawasaki disease and PFAPA syndrome.
Treatment
Initial management includes ensuring airway, breathing, and circulation stability. Treatment is directed at the underlying cause and should account for local resistance patterns, including CA-MRSA prevalence. Outpatient therapy typically lasts 7–10 days and includes limb elevation, moist heat, analgesics, and antibiotics. Abscesses require drainage with culture when possible. Skin-source infections are commonly treated with oral cephalexin plus trimethoprim–sulfamethoxazole or alternatives such as clindamycin or doxycycline. Pharyngeal or periodontal sources are treated with penicillin VK or alternatives such as clindamycin or amoxicillin–clavulanate. Inpatient therapy may require IV penicillin-based regimens with MRSA coverage using vancomycin or clindamycin when indicated.
Disposition and follow-up
Admission is indicated for toxic-appearing patients, those with immunosuppression or significant comorbidities, inability to tolerate oral therapy, or unreliable follow-up. Patients with mild infection who are nontoxic, can take oral antibiotics, and have reliable follow-up within 24–48 hours may be discharged. Failure to resolve promptly with antibiotics should prompt evaluation for malignancy or other serious causes, and lymph node biopsy may be indicated for persistent, large, or supraclavicular nodes.
Pearls and pitfalls
Staphylococcus species are the most common cause of acute regional pyogenic lymphadenitis. Empiric antibiotic therapy should include coverage for CA-MRSA in addition to streptococci, particularly in unresponsive or high-risk infections.

​Emergency and Acute Medicine – Lyme Disease
Basics description
Lyme disease is the most common tick-borne illness in North America. It is endemic in the northeastern United States, the upper Midwest, and parts of northwestern California. The disease follows a multisystem course and may present with dermatologic, neurologic, cardiac, and musculoskeletal manifestations.
Etiology and pathophysiology
Lyme disease is caused by the spirochete Borrelia burgdorferi, which is transmitted through the bite of an Ixodes tick, most commonly Ixodes dammini (the deer tick). Transmission occurs primarily between April and November, with 80–90% of cases in the summer months. Fewer than half of patients recall a tick bite. Disease pathogenesis involves organism-induced local inflammation, cytokine release, and autoimmune mechanisms. There is no person-to-person transmission. A related spirochete, Borrelia miyamotoi, has also been identified as a cause of a Lyme-like illness.
Clinical presentation and stages
Lyme disease progresses through three clinical stages, although not all patients experience every stage.
Stage I, or early localized disease, begins days to weeks after a tick bite. The hallmark finding is erythema chronicum migrans, a pathognomonic expanding annular rash greater than 5 cm in diameter, often with central clearing and a red outer border (“bull’s-eye” rash). Associated symptoms include regional lymphadenopathy, low-grade fever, headache, myalgias, arthralgias, fatigue, and malaise.
Stage II, or early disseminated disease, occurs days to weeks after infection and is characterized by intermittent, fluctuating symptoms. Neurologic involvement includes the triad of aseptic meningitis, cranial neuritis, and radiculoneuritis, with facial (Bell) palsy being the most common cranial nerve deficit. Cardiac manifestations may include tachycardia, bradycardia, atrioventricular block, and myopericarditis. Rash may be absent at this stage. Prognosis is generally good with appropriate treatment.
Stage III, or late disease, develops months to years after initial infection. Musculoskeletal involvement is most common, typically presenting as recurrent monoarticular or oligoarticular arthritis, most often affecting the knee. Dermatologic findings may include acrodermatitis chronica atrophicans on the extensor surfaces of the extremities. Less commonly, late neurologic complications such as chronic polyneuropathy or encephalopathy may occur. A Jarisch–Herxheimer reaction, consisting of transient symptom worsening shortly after treatment initiation, may be seen.
Special populations
Children are more likely than adults to present with fever and may lack a history of erythema migrans. Facial palsy in pediatric patients is frequently associated with aseptic meningitis. Cardiac involvement may be asymptomatic but detectable on ECG. With appropriate treatment, children generally have excellent long-term outcomes. There is no clear evidence that Lyme disease during pregnancy causes fetal harm.
Diagnosis and evaluation
Lyme disease is primarily a clinical diagnosis. The presence of erythema migrans eliminates the need for serologic testing. In patients without the classic rash, serologic testing with ELISA followed by confirmatory Western blot is indicated. Lumbar puncture is reserved for patients with meningeal signs, arthrocentesis for acute arthritis, and ECG for suspected cardiac involvement.
Laboratory findings are nonspecific and may include elevated erythrocyte sedimentation rate, mild cytopenias, or elevated liver enzymes. Cerebrospinal fluid analysis may show pleocytosis and elevated protein in neuroborreliosis.
Differential diagnosis
The differential diagnosis includes other tick-borne illnesses, viral meningitis, septic arthritis, rheumatic fever, syphilis, parvovirus B19 infection, infectious endocarditis, juvenile idiopathic arthritis, fibromyalgia, and chronic fatigue syndrome.
Treatment
Initial stabilization focuses on hydration, IV access for neurologic or cardiac involvement, and cardiac monitoring when indicated. Tick removal should be performed promptly using blunt forceps applied close to the skin.
Antibiotic therapy depends on disease stage and severity. Early localized disease is treated with oral antibiotics such as amoxicillin, doxycycline (for patients ≥8 years old and nonpregnant), or cefuroxime. Disseminated disease with mild neurologic involvement may be treated orally, while meningitis, significant carditis, or severe arthritis requires parenteral therapy, typically with ceftriaxone, cefotaxime, or penicillin G. Late disease usually requires prolonged parenteral therapy. NSAIDs are used for arthralgias and arthritis, and aspirin may be used adjunctively in cardiac involvement.
Disposition and follow-up
Hospital admission is required for patients with meningoencephalitis or significant cardiac involvement requiring telemetry or ICU monitoring. Patients with uncomplicated disease treated with oral antibiotics may be discharged with close outpatient follow-up.
Key points
Early recognition and treatment of Lyme disease prevent late complications. The presence of erythema migrans is diagnostic and should prompt immediate treatment without waiting for serology. Clinicians should remain vigilant for coinfections such as anaplasmosis and babesiosis in endemic regions, and prolonged treatment is required for later-stage organ involvement.

KembaraXtra-Medicine – Autism Spectrum Disorder


Autism spectrum disorder (ASD) is a biologically based neurodevelopmental disorder that includes a range of developmental disabilities. It is defined by early-appearing social-communication difficulties and restricted, repetitive patterns of behavior, interests, or activities. ASD describes a constellation of social communication deficits and repetitive sensorimotor behaviors, often with a strong genetic component and sometimes other identifiable causes. Outcomes today are generally better than decades ago, with more individuals able to communicate, learn, and live in the community, though many still require ongoing support into adulthood. Clinicians play an important role by helping families access evaluations, referrals, and community resources, and by anticipating major transitions such as starting school and moving into adult services.


Diagnosis is based on DSM-5-TR or ICD-11 criteria. DSM-5-TR requires persistent deficits in social communication and social interaction across multiple contexts (including social-emotional reciprocity, nonverbal communication, and relationships) plus restricted/repetitive patterns of behavior (such as stereotyped movements or speech, insistence on sameness, restricted interests, and sensory hyper- or hyporeactivity). ASD can be further described by whether intellectual disability, language impairment, medical/genetic conditions, or catatonia are present. Comorbid intellectual disability, neurologic/medical problems, and psychiatric disorders are common, and symptom severity varies widely between individuals.


ASD affects an estimated 1% to 3% of children in the United States, with prevalence often described as approximately 1 in 40 children. Rates have increased over recent decades, but it is unclear whether this reflects broader criteria, increased awareness and diagnostic accuracy, or a true rise in frequency. ASD is more common in males, with an estimated male-to-female ratio of about 3:1. Most children are identified by age 4, often because of delayed communication milestones, though presentation and timing of diagnosis can vary depending on language, cognition, and adaptive functioning.


Risk factors include several prenatal and perinatal factors such as hypoxia-related obstetric complications, prenatal infections, maternal use of certain medications (notably valproic acid), maternal health conditions (diabetes, hypertension, obesity, preeclampsia), advanced parental age, multiple gestation, prematurity, and congenital sensory deficits. Environmental exposures have also been associated in some studies, including significant air pollution exposure during pregnancy and early life and heavy maternal smoking. ASD is highly heritable, with an estimated heritability around 80%. Concordance rates rise with genetic relatedness, and research has identified many genetic contributors including polygenic risk and rare variants such as copy number variants. Neurobiologic studies show brain differences in some individuals with ASD, including atypical connectivity and cortical structural differences, but these findings are not diagnostic.


Clinically, ASD is often described by a triad: impairment in social interaction, atypical verbal and nonverbal communication, and repetitive or unusual behaviors. Social difficulties can include poor social-emotional reciprocity and reduced shared attention. Communication may be affected through limited gestures, reduced facial expression, or difficulty using and interpreting nonverbal signals. Repetitive features may include stereotyped movements (such as hand flapping or rocking), repetitive speech (including echolalia), and strong preferences for sameness or routine. Sensory differences are common, including hypersensitivity to sound, touch, or smells, or hyposensitivity such as unusually high pain tolerance. Catatonia can appear in up to 20% of adolescents and adults with ASD.


Many conditions and syndromes are associated with ASD. Approximately 20% to 50% of individuals have intellectual disability, about 50% have ADHD, around 25% have an associated genetic syndrome, and roughly 12% have epilepsy. Examples of associated syndromes include fragile X syndrome, tuberous sclerosis, Angelman syndrome, Rett syndrome, Down syndrome, and DiGeorge syndrome, among others.


The differential diagnosis includes other psychiatric and neurodevelopmental disorders that may share overlapping features, such as ADHD, Tourette syndrome, selective mutism, catatonia, social anxiety, obsessive-compulsive disorder, language disorders, stereotypic movement disorder, and intellectual disability. Social (pragmatic) communication disorder is an important distinction because it involves social communication deficits without the restricted/repetitive behaviors required for ASD. Attachment disorders can also mimic aspects of ASD, particularly in children with histories of early neglect.


Workup focuses on confirming diagnosis and identifying contributing or associated medical conditions, including genetic syndromes. “Red flags” in early social communication should prompt evaluation, such as no vocalizations by 6 months, no consonant babbling by 12 months, no gestures by 12 months, no spontaneous single words by 16 months, no spontaneous phrases by 24 months, or any loss of previously acquired social-communication skills. The American Academy of Pediatrics and the CDC recommend formal ASD screening at 18 and 24 months. Gold-standard assessment includes detailed developmental and family history, evaluation of intellectual/developmental functioning, direct assessment of ASD symptoms, and measurement of adaptive functioning, with additional language, neuropsychologic, motor, or psychiatric assessments as needed.


Laboratory testing may include newborn screening review (such as PKU), lead screening, hearing assessment, and genetic testing (karyotype, chromosome microarray, and targeted DNA testing when indicated). Creatine kinase and TSH may be considered when motor concerns are present. An EEG is recommended when seizures are suspected or when there is language regression. Brain imaging is recommended if macrocephaly, microcephaly, or abnormal tone/motor findings are present.


Treatment emphasizes early and structured intervention. Nonpharmacologic therapy includes behavioral programs at home and school, applied behavioral analysis (ABA) approaches (such as Discrete Trial Training), and development-focused ABA models (such as Pivotal Response Training, Floortime, and the Early Start Denver Model). Specialized educational approaches focusing on communication and life skills (such as TEACCH) are often helpful. Cognitive-behavioral therapy can reduce anxiety in higher-functioning individuals. Family and teacher education and highly structured environments support skill-building and daily functioning.


Medication does not “cure” ASD, but can reduce specific target symptoms. Risperidone and aripiprazole are FDA-approved for managing irritability associated with ASD. Other medications are used off-label depending on symptoms, including SSRIs or atypical antipsychotics for obsessive or ritualistic behaviors, atypical antipsychotics and other agents for aggression or self-injury, stimulants or alpha-2 agonists for hyperactivity/inattention, and SSRIs or other agents for anxiety or depression. Catatonia is treated with lorazepam and sometimes electroconvulsive therapy, and antipsychotics should be avoided in catatonia because they can worsen it. Complementary approaches have limited evidence overall, though melatonin has preliminary evidence for sleep difficulties.


Most individuals with ASD require some level of support as adults. DSM-5-TR describes severity levels based on support needs, from Level 1 (requiring support) to Level 3 (requiring very substantial support). Better outcomes are linked to early identification and intervention, development of functional spoken language, and capacity for inclusion with typical peers. Poorer outcomes are associated with lack of joint attention by age 4, absence of functional speech by age 5, intellectual disability, seizures, significant comorbid medical or psychiatric conditions, and pervasive social disengagement. Referrals may involve specialists for diagnosis (developmental pediatrics, child psychiatry, psychology, neurology, genetics) and therapy services (speech-language therapy, occupational therapy, behavioral therapy), as well as support for caregivers and school planning.


There is no scientific evidence linking childhood vaccination to the development of ASD. Many individuals with ASD have increased rates of medical issues such as sleep problems, gastrointestinal concerns, and oral health problems, and psychiatric comorbidities are common across the lifespan.