Henoch-Schonlein purpura
Summary
Henoch-Schönlein purpura (HSP), now termed IgA vasculitis, is the most common childhood systemic vasculitis, characterized by IgA immune complex deposition causing a classic tetrad: palpable purpura (buttocks/legs), arthralgia, abdominal pain, and renal disease. It often follows an upper respiratory infection and is self-limited in most cases.
Detail
Pathophysiology: HSP is a small-vessel leukocytoclastic vasculitis caused by IgA1-dominant immune complex deposition in vessel walls, particularly in skin, joints, GI tract, and kidneys (mesangium). It is often triggered by an upper respiratory tract infection (commonly Group A Streptococcus) 1-3 weeks prior, though many cases are idiopathic. It shares pathogenic overlap with IgA nephropathy (Berger disease), and some consider them a spectrum of the same disease.
Clinical Features (classic tetrad): 1. Palpable purpura - symmetric, on buttocks and lower extremities, due to vasculitis without thrombocytopenia (platelet count normal) 2. Arthralgia/arthritis - typically large joints (knees, ankles), migratory, non-deforming 3. Abdominal pain - due to bowel wall edema/hemorrhage; can cause intussusception (classically ileo-ileal, unlike typical ileocolic intussusception), melena, or GI bleeding 4. Renal disease - IgA nephropathy-like glomerulonephritis; presents with hematuria +/- proteinuria; can progress to nephrotic syndrome or chronic kidney disease in a minority
Epidemiology: Most common in children ages 3-15, slight male predominance, peak incidence in fall/winter following viral/bacterial URIs.
Diagnosis: Primarily clinical based on EULAR/PRINTO/PRES criteria (palpable purpura plus one of: abdominal pain, arthritis/arthralgia, renal involvement, or IgA deposition on biopsy). Skin or renal biopsy shows IgA and C3 deposition on immunofluorescence. Labs are typically normal (platelets, coagulation studies) which helps distinguish from other causes of purpura like ITP or meningococcemia.
Management: Mostly supportive care (hydration, NSAIDs for joint pain - avoid in renal impairment). Corticosteroids may be used for severe abdominal pain or significant renal involvement. Most cases resolve within 4-6 weeks. Renal function should be monitored for months after since nephropathy can develop or worsen even after other symptoms resolve.
Prognosis: Generally excellent in children; may recur in up to 1/3 of patients. Renal involvement is the most important predictor of long-term morbidity - a minority progress to chronic kidney disease or end-stage renal disease, especially if there is nephrotic-range proteinuria or crescentic glomerulonephritis on biopsy.
High-Yield Associations: Normal platelet count/coagulation studies (distinguishes from ITP, DIC), association with recent URI/streptococcal infection, association with intussusception in children, and overlap with IgA nephropathy pathophysiology.
Sources
- First Aid for the USMLE Step 1
- Robbins and Cotran Pathologic Basis of Disease
- UpToDate: IgA vasculitis (Henoch-Schönlein purpura)
- Kaplan USMLE Step 1 Lecture Notes: Pathology
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