A 52-year-old woman presents with a 2-week history of fever, malaise, and a palpable purpura on the lower extremities and buttocks. Laboratory investigations show elevated inflammatory markers and microscopic hematuria. Skin biopsy reveals IgA immune complex deposition on immunofluorescence. All of the following statements regarding IgA vasculitis (formerly Henoch–Schönlein purpura) are correct EXCEPT:

Question

Accepted Answer

D. The disease is mediated by circulating ANCA antibodies, particularly anti-MPO and anti-PR3. ## Pathogenesis and Classification of IgA Vasculitis

**Key Point:** IgA vasculitis (IgAV) is an **ANCA-negative** small-vessel vasculitis mediated by IgA immune complex deposition, NOT by ANCA antibodies. This is a critical distinction from ANCA-associated vasculitides.

### Immune Mechanism Comparison

| Vasculitis Type | Immune Mechanism | ANCA Status | Vessel Size |
|---|---|---|---|
| **IgA Vasculitis** | IgA immune complex deposition | ANCA-negative | Small vessel |
| **GPA** | ANCA (anti-PR3) + immune complexes | ANCA-positive (c-ANCA) | Small-to-medium |
| **MPA** | ANCA (anti-MPO) | ANCA-positive (p-ANCA) | Small vessel |
| **EGPA** | ANCA (anti-MPO, variable) | ANCA-positive (p-ANCA) | Small-to-medium |

**High-Yield:** IgA vasculitis is **NOT** an ANCA-associated vasculitis. The presence of ANCA antibodies (anti-MPO or anti-PR3) would indicate a different diagnosis (GPA, MPA, or EGPA) and would be atypical in IgAV.

### Clinical Features of IgA Vasculitis

**Mnemonic:** **SKIN** = **S**kin palpable purpura (lower extremities, buttocks), **K**idney (IgA nephropathy), **I**ntestinal (abdominal pain, GI bleeding), **N**ot ANCA-mediated.

### Renal Involvement

**Clinical Pearl:** Renal involvement occurs in 40–50% of adults with IgAV and is more severe than in children. Histologically, it presents as IgA nephropathy with mesangial proliferation and, in severe cases, crescent formation. Renal prognosis is the main determinant of long-term outcomes.

### Gastrointestinal Involvement

- Abdominal pain (colicky, periumbilical)
- GI bleeding (melena, hematochezia)
- Intussusception (more common in children)
- Rarely, bowel perforation or pancreatitis

[cite:Harrison 21e Ch 319; Robbins 10e Ch 11]

Answer

A. Gastrointestinal involvement can present with abdominal pain, bleeding, and rarely intussusception in children

Answer

B. IgA vasculitis is the most common systemic vasculitis in children but can occur in adults with worse prognosis

Answer

C. Renal involvement manifests as IgA nephropathy with crescent formation in severe cases

Explanation

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