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Medium & Variable-Sized Vasculitis for USMLE Step 3

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Medium & Variable-Sized Vasculitis for the USMLE Step 3 Exam
Medium and variable-sized vasculitis primarily includes Polyarteritis Nodosa (PAN), Kawasaki Disease, Thromboangiitis Obliterans (Buerger’s Disease), and Behçet’s Disease. These disorders involve inflammation in medium-sized vessels, though Behçet’s Disease affects vessels of multiple sizes.
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Polyarteritis Nodosa (PAN)
  • Definition:
    • PAN is a necrotizing vasculitis of medium-sized arteries, typically sparing small vessels, with a predilection for the kidneys, GI tract, skin, and peripheral nerves.
  • Epidemiology:
    • Most common in middle-aged adults, with a slight male predominance; may be associated with hepatitis B virus (HBV) infection.
  • Pathophysiology:
    • Immune-mediated inflammation leads to transmural necrosis, microaneurysm formation, and ischemic injury in affected organs.
  • Clinical Presentation:
    • Systemic: Fever, weight loss, and fatigue.
    • Renal: Hypertension and ischemia, but usually no glomerulonephritis.
    • Neurologic: Mononeuritis multiplex with asymmetric motor and sensory deficits.
    • Gastrointestinal: Postprandial abdominal pain and mesenteric ischemia.
    • Dermatologic: Livedo reticularis, subcutaneous nodules, and ulcerations.
Polyarteritis Nodosa
  • Diagnosis:
    • Laboratory: Elevated ESR/CRP and hepatitis B serologies in HBV-associated cases.
    • Biopsy: Shows transmural inflammation and fibrinoid necrosis in medium arteries.
    • Angiography: Useful to identify microaneurysms and “beading” in mesenteric or renal arteries.
  • Management:
    • Corticosteroids: Main treatment.
    • Cyclophosphamide: Added in severe cases.
    • Antivirals: For HBV-associated PAN, in combination with corticosteroids.
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Kawasaki Disease
  • Definition:
    • A self-limited vasculitis affecting medium-sized arteries, particularly the coronary arteries, in children.
  • Epidemiology:
    • Primarily affects children <5 years old, with higher incidence in Asian populations.
  • Pathophysiology:
    • Likely due to an infectious trigger in genetically predisposed children, leading to immune-mediated coronary artery inflammation.
  • Clinical Presentation:
    • Fever: Prolonged fever lasting >5 days.
    • Additional Criteria (4 out of 5):
    • Bilateral conjunctivitis.
    • Oral mucosal changes (strawberry tongue, cracked lips).
    • Polymorphous rash.
    • Extremity changes (swelling, erythema, desquamation).
    • Cervical lymphadenopathy >1.5 cm.
  • Complications:
    • Coronary artery aneurysms may develop, risking myocardial infarction.
  • Diagnosis:
    • Based on clinical criteria; elevated ESR/CRP and thrombocytosis.
    • Echocardiography: Monitors for coronary artery aneurysms.
  • Management:
    • IVIG: Reduces coronary aneurysm risk when given within the first 10 days.
    • Aspirin: High-dose during acute phase, followed by low-dose for antithrombotic effect.
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Thromboangiitis Obliterans (Buerger’s Disease)
  • Definition:
    • A non-atherosclerotic vasculitis affecting small- and medium-sized vessels, linked to smoking.
  • Epidemiology:
    • Occurs mostly in young male smokers, typically under 45 years old.
  • Pathophysiology:
    • Tobacco-induced immune response damages the endothelium, leading to thrombosis and inflammation in distal vessels.
  • Clinical Presentation:
    • Ischemia: Claudication, rest pain, and gangrene of distal extremities.
    • Raynaud’s Phenomenon: Episodic color changes in response to cold.
    • Migratory Superficial Thrombophlebitis: Red, tender cords along superficial veins.
  • Diagnosis:
    • Angiography: Shows “corkscrew” collaterals in the distal vessels.
    • Clinical: Strong association with smoking history and ischemic symptoms.
  • Management:
    • Smoking Cessation: Essential to prevent progression; no effective pharmacologic treatments if smoking continues.
    • Symptomatic Care: Analgesics and wound care; amputation in severe cases.
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Behçet’s Disease
  • Definition:
    • Variable vessel vasculitis affecting vessels of all sizes, characterized by recurrent oral and genital ulcers, uveitis, and systemic inflammation.
  • Epidemiology:
    • Most common in the Middle East and East Asia, typically affecting young adults.
  • Pathophysiology:
    • Suspected abnormal immune response to environmental triggers in genetically susceptible individuals, causing inflammation in vessels of all sizes.
  • Clinical Presentation:
    • Oral and Genital Ulcers: Painful, recurrent.
    • Ocular: Uveitis, which can lead to blindness.
    • Skin Lesions: Erythema nodosum and acneiform eruptions.
    • Vascular: Venous thrombosis and arterial aneurysms.
  • Diagnosis:
    • Based on clinical criteria: recurrent oral ulcers plus two of the following—genital ulcers, uveitis, skin lesions, or a positive pathergy test.
  • Management:
    • Corticosteroids: For acute flares.
    • Immunosuppressive Therapy: Azathioprine, TNF inhibitors, or cyclosporine for chronic, severe cases.
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Key Points
  • Polyarteritis Nodosa (PAN):
    • Medium-vessel vasculitis causing hypertension, neuropathy, and GI ischemia.
    • Diagnosed by biopsy or angiography; treated with corticosteroids and immunosuppressants.
  • Kawasaki Disease:
    • Pediatric vasculitis affecting coronary arteries with risk of aneurysms.
    • Diagnosed clinically; managed with IVIG and aspirin.
  • Thromboangiitis Obliterans (Buerger’s Disease):
    • Strongly associated with smoking, affecting small and medium vessels of extremities.
    • Smoking cessation is essential to prevent progression.
  • Behçet’s Disease:
    • Variable vessel vasculitis with recurrent oral/genital ulcers and uveitis.
    • Managed with corticosteroids for flares and immunosuppressants for severe cases.

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