Diagnosis of Henoch-Schönlein Purpura
The diagnosis of Henoch-Schönlein purpura (HSP, now called IgA vasculitis) is confirmed by the presence of palpable purpura plus at least one of the following: diffuse abdominal pain, arthritis/arthralgia, renal involvement (hematuria and/or proteinuria), or a biopsy showing predominant IgA deposition. 1, 2
Clinical Diagnostic Criteria
The diagnosis is primarily clinical and does not require biopsy in typical presentations. You need:
Required finding:
- Non-thrombocytopenic palpable purpura (confirm platelet count is normal to exclude other causes)
Plus at least ONE of:
- Diffuse abdominal pain (often periumbilical, worsens with meals)
- Arthritis or arthralgia (typically affecting knees and ankles)
- Renal involvement: hematuria and/or proteinuria
- Biopsy showing leukocytoclastic vasculitis with IgA deposition 1, 2, 3
When to Perform Biopsy
Skin biopsy is indicated when:
- Clinical presentation is atypical or unclear
- You need to differentiate HSP from other vasculitides or inflammatory bowel disease
- Adult patients (who more commonly have atypical presentations)
Renal biopsy is indicated when:
- Significant proteinuria or declining renal function is present
- You need to assess severity of nephritis to guide treatment decisions 4
What Biopsy Shows
Skin biopsy findings:
- Leukocytoclastic vasculitis in small vessels
- Direct immunofluorescence (DIF) showing IgA deposition in vessel walls - this is the definitive confirmatory finding 5, 2, 6
Renal biopsy findings:
- Mesangial IgA deposits (pathognomonic)
- Crescentic necrotizing glomerulonephritis in severe cases 4
Essential Laboratory Evaluation
Perform these tests to confirm diagnosis and assess complications:
- Complete blood count - must show normal platelet count (excludes thrombocytopenic purpura)
- Urinalysis - check for hematuria and proteinuria (present in 20-50% of cases)
- Serum creatinine - assess renal function
- Stool guaiac - detect occult GI bleeding 1, 6
Key Diagnostic Pitfalls
Do NOT confuse classification criteria with diagnostic criteria. The 1990 ACR criteria and 2022 ACR-EULAR criteria were developed to classify patients already known to have vasculitis, not to diagnose HSP de novo 2.
In adults presenting with purpura, abdominal pain, and GI symptoms: The clinical picture can mimic inflammatory bowel disease. The distinguishing feature is IgA deposition on DIF of skin biopsy, which confirms HSP rather than IBD 5.
When renal involvement and systemic vasculitis features are prominent: HSP can be clinically indistinguishable from other ANCA-associated vasculitides. Immunofluorescent study of renal biopsy showing mesangial IgA deposits is vital to establish the correct diagnosis 4.
Imaging When Indicated
Abdominal ultrasound or CT should be obtained if:
- Severe abdominal pain is present (to detect intussusception - the most common surgical complication)
- You suspect bowel perforation
- Findings show asymmetric bowel wall thickening, typically in jejunum and ileum 6