A 32-year-old woman from Delhi presents with a 5-day history of gross haematuria, bilateral flank pain, and fever (38.5°C). She has a history of recurrent sinusitis. On examination, BP is 156/98 mmHg, and she has a palpable purpuric rash on the lower extremities and buttocks. Urinalysis shows 4+ proteinuria, dysmorphic RBCs, and RBC casts. Serum creatinine is 2.1 mg/dL. Complement C3 and C4 levels are normal. ANCA is negative. What is the most likely diagnosis?

Explanation

## Clinical Presentation Analysis **Key Point:** IgA vasculitis (formerly Henoch–Schönlein purpura) is a small-vessel vasculitis characterized by the tetrad of palpable purpura, arthritis/arthralgia, renal involvement (haematuria/proteinuria), and abdominal pain. ### Diagnostic Features of IgA Vasculitis | Feature | IgA Vasculitis | ANCA-AAV | Anti-GBM | Cryoglobulinaemia | |---------|---|---|---|---| | **Palpable purpura** | Yes (lower extremities, buttocks) | Rare | No | Rare | | **Renal involvement** | Yes (IgA-dominant on biopsy) | Yes (ANCA+) | Yes (linear IgG) | Yes | | **Complement levels** | Normal | Normal | Normal | Low C4, normal C3 | | **ANCA** | Negative | Positive (MPO or PR3) | Negative | Negative | | **Associated conditions** | Sinusitis, URI | Respiratory/ENT | Pulmonary haemorrhage | Hepatitis C, lymphoma | | **Skin biopsy** | IgA deposition | ANCA+ on immunofluorescence | Linear IgG on GBM | Cryoglobulins in serum | **High-Yield:** The combination of: - **Palpable purpura on buttocks and lower extremities** (pathognomonic distribution) - Acute nephritic syndrome (haematuria, RBC casts, AKI) - **Normal complement levels** (excludes post-infectious GN and lupus) - **Negative ANCA** (excludes vasculitis-associated GN) - History of recurrent sinusitis (IgA vasculitis can follow URI) points to IgA vasculitis. ### Pathophysiology 1. IgA-immune complex deposition in skin, joints, GI tract, and kidneys 2. Small-vessel vasculitis → endothelial injury 3. Kidney biopsy shows IgA-dominant glomerulonephritis (mesangial proliferation) 4. Skin biopsy shows IgA deposition in dermal vessels **Clinical Pearl:** IgA vasculitis is the most common primary vasculitis in children but can present in adults. Renal involvement (haematuria ± proteinuria) occurs in 80% of cases and is the major determinant of prognosis. Persistent proteinuria >1 g/day predicts chronic kidney disease. **Mnemonic:** **SPAR** — Skin (palpable purpura), Purpura (buttocks/legs), Arthritis/Abdominal pain, Renal involvement. All four features present = IgA vasculitis. **Warning:** Do not confuse with ANCA-associated vasculitis — ANCA is negative in IgA vasculitis and positive in granulomatosis with polyangiitis (GPA) or microscopic polyangiitis (MPA).