A 5 year old boy presents with abdominal pain, a rash over his lower limbs, and a painful right ankle for 2 days, preceded by fever for a week. He had a sore throat around 2 weeks back. His medical history is unremarkable. There is no history of recent vaccinations, and no known allergies to foods or drugs.
WBC: 10,200/mm3 (5,000-17,000) Hb: 12.4 g/dL (11.5-13.5) Platelets: 380,000/mm3 (150,000-450,000)
ESR: 32 mm/1h (0-10) CRP: 22.1 mg/L (<10)
The Urinalysis shows 6 to 8 erythrocytes / high powered field. Blood Urea: 3.4 mmol/L (2.5-6.5) S. Creatinine: 38 micromol/L (20-80)
A leukocytoclastic vasculitis is noted. Direct immunofluorescence microscopy shows perivascular deposition of IgA.