IgA Vasculitis (Henoch-Schönlein Purpura)
Rheumatology
Illness script · Rheumatology
IgA Vasculitis (Henoch-Schönlein Purpura)
Small-vessel IgA-mediated leukocytoclastic vasculitis causing the classic tetrad of palpable purpura, arthritis, abdominal pain, and renal disease.
This illness script for IgA Vasculitis (Henoch-Schönlein Purpura) covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Most common systemic vasculitis in children; peak age 3–10 years
- Male predominance (2:1)
- Often preceded by upper respiratory infection (esp. Group A Strep)
- Can occur in adults but more severe renal involvement
- Seasonal clustering in fall/winter
- Triggers: infections, drugs, vaccinations (rare)
02
Presentation
- Classic tetrad: palpable purpura + arthritis + abdominal pain + renal disease
- Purpura: non-thrombocytopenic, gravity-dependent, lower extremities and buttocks
- Arthritis: transient, non-migratory, large joints (knees, ankles)
- Colicky abdominal pain; intussusception is a feared complication
- Renal: hematuria/proteinuria; usually appears 4–6 weeks after rash
- Normal platelet count distinguishes from ITP/TTP
03
Pathophysiology
- IgA1 glycosylation defect → IgA immune complex deposition in vessel walls
- IgA complexes activate complement → neutrophil-mediated vascular inflammation
- Small vessel walls (skin, gut, joints, glomeruli) are preferentially affected
- Renal IgA deposition mirrors IgA nephropathy pathology
04
Diagnostics
- Diagnosis is clinical; biopsy is gold standard if uncertain
- Skin or renal biopsy: IgA deposits on immunofluorescence (pathognomonic)
- UA: microscopic hematuria ± proteinuria — check in all patients
- Platelets NORMAL (rules out thrombocytopenic purpura)
- Elevated IgA levels in ~50% — supportive but not required
05
Management
- Most cases self-limited; supportive care with hydration and NSAIDs for joint pain
- Monitor renal function/UA weekly for 6 weeks after presentation
- Steroids (prednisone) for severe abdominal pain or significant renal involvement
- ACE inhibitor/ARB for persistent proteinuria
- Long-term follow-up needed: rare progression to chronic kidney disease in adults
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Idiopathic Thrombocytopenic Purpura (ITP)
HSP has NORMAL platelets and systemic tetrad; ITP has isolated thrombocytopenia with no renal/GI involvement.
IgA Nephropathy (Berger disease)
IgA nephropathy is renal-limited hematuria following mucosal infection; HSP has the full systemic tetrad with purpura.
Meningococcemia
Meningococcemia purpura is non-palpable/petechial, involves trunk/face, and presents with sepsis/fever — not lower-extremity palpable purpura.
Reactive Arthritis
Reactive arthritis follows genitourinary/GI infection with triad of urethritis, arthritis, conjunctivitis — no purpura or IgA deposits.
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.