Primary Vasculitides of Childhood
Small-vessel disease
IgA vasculitis (Henoch-Schönlein) is the commonest childhood vasculitis: palpable purpura on dependent areas, arthritis, abdominal pain, and nephritis. It is a clinical diagnosis; monitor blood pressure and urinalysis for at least 6 months. ANCA-associated vasculitis - granulomatosis with polyangiitis (PR3-ANCA) and microscopic polyangiitis (MPO-ANCA) - causes sinusitis, pulmonary nodules, and glomerulonephritis.
Medium- and large-vessel disease
Kawasaki disease is the priority: fever for at least 5 days plus 4 of 5 features (bilateral conjunctival injection, oral changes, polymorphous rash, extremity changes, cervical lymphadenopathy); incomplete disease is common in infants under 6 months. Treat with IVIG 2 g/kg and aspirin within 10 days; coronary artery z-scores guide follow-up. Polyarteritis nodosa causes fever, myalgia, hypertension, and microaneurysms without glomerulonephritis. Takayasu arteritis presents in adolescent girls with unequal pulses, blood pressure discrepancy, and hypertension.
Traps
A child with prolonged fever, red eyes, and cracked lips needs an echocardiogram even if criteria are incomplete. Live vaccines should be deferred after high-dose IVIG. A negative ANCA does not exclude vasculitis.
Rule of thumb
Palpable purpura below the waist with abdominal pain is IgA vasculitis until urinalysis proves otherwise; persistent fever with conjunctivitis and mucositis is Kawasaki until echocardiography proves otherwise.