A 58-year-old man presents with constitutional symptoms, palpable purpura on lower extremities, and glomerulonephritis. Serum complement levels are normal. Which of the following is NOT a characteristic feature of polyarteritis nodosa (PAN)?

## Polyarteritis Nodosa (PAN) — Key Distinguishing Features ### Pathologic Hallmarks **Key Point:** PAN is a systemic necrotizing vasculitis of **medium-sized muscular arteries** with characteristic segmental transmural inflammation, fibrinoid necrosis, and immune complex deposition. **High-Yield:** PAN classically **spares the lungs, glomeruli, and skin** — this is a critical distinguishing feature from other vasculitides. When skin involvement occurs, it manifests as nodules or livedo reticularis, NOT palpable purpura. ### Why Option 1 (Glomerulonephritis with IgA Deposition) Is WRONG PAN does **NOT** typically cause glomerulonephritis. When renal involvement occurs in PAN, it is due to **renal artery vasculitis** (causing renal infarction or hypertension), NOT glomerulonephritis. IgA-dominant glomerulonephritis is the hallmark of **IgA vasculitis (formerly Henoch–Schönlein purpura)**, a small-vessel vasculitis affecting skin, joints, GI tract, and kidneys. ### Correct Features of PAN (Options 0, 2, 3) | Feature | Details | |---------|----------| | **Transmural inflammation** | Segmental necrosis of medium-sized arteries with fibrinoid necrosis | | **Organ sparing** | Lungs and glomeruli typically spared (unless renal artery involved) | | **Hepatitis B association** | 5–10% of PAN cases are HBsAg-positive; immune complex-mediated | ### Clinical Pearls **Clinical Pearl:** The triad of **constitutional symptoms + palpable purpura + renal disease** in the stem is actually more suggestive of **IgA vasculitis** or **ANCA-associated vasculitis** than PAN. PAN would present with constitutional symptoms, livedo reticularis or nodules, and renal artery involvement (not glomerulonephritis). **Mnemonic — PAN vs. Other Vasculitides (SPONGE):** - **S**mall vessels → IgA vasculitis, ANCA-associated - **P**AN → Medium vessels, lungs/glomeruli spared - **O**rgan-specific → Takayasu, GCA (large vessels) - **N**ormal complement → PAN, ANCA-associated - **G**lomerulonephritis → IgA vasculitis, ANCA-associated (NOT PAN) - **E**ndothelial → All vasculitides [cite:Robbins 10e Ch 11]