IgA vasculitis — branching viva

Emergency department: a five-year-old boy, one week after a sore throat, with a raised purplish rash on his lower legs and ankles, swollen painful knees, colicky abdominal pain, and a urinalysis showing microscopic haematuria with trace protein. The examiner asks: name the diagnosis and give the classification criteria, then branches to the corticosteroid decision and the evidence that prednisone does not prevent the nephropathy, to the same boy re-presenting with severe worsening abdominal pain and bile-stained vomiting that opens the intussusception and its surgical interface, and finally to a nephrotic-range proteinuria with hypertension that opens the renal biopsy and the immunosuppression pathway.