Polyarteritis nodosa (PAN) is a necrotizing vasculitis of medium-sized arteries. Which feature distinguishes PAN from granulomatosis with polyangiitis (GPA, formerly Wegener) on pathological examination, and what is the serological marker for GPA?

• A PAN is ANCA-positive (p-ANCA/MPO-ANCA), involves lung parenchyma with alveolar hemorrhage, and shows pauci-immune glomerulonephritis
• B PAN shows IgA-dominant immune deposits in vessel walls; GPA shows ANCA without immune deposits (pauci-immune)
• C PAN and GPA are both associated with HBsAg positivity; the only difference is vessel size
• D PAN spares the lungs and kidneys glomeruli, involves only medium arteries, shows fibrinoid necrosis without granulomas, and is ANCA-negative; GPA shows granulomatous necrotizing vasculitis of small vessels with c-ANCA (PR3-ANCA) ✓

Explanation

PAN is a segmental necrotizing vasculitis of medium-sized arteries (renal, hepatic, mesenteric) that characteristically spares pulmonary arteries and glomerular capillaries. Histology shows fibrinoid necrosis and mixed inflammatory infiltrate but NO granulomas and NO ANCA (classical PAN is ANCA-negative; ~30% associated with hepatitis B). GPA is an ANCA-associated vasculitis (c-ANCA/PR3-ANCA in ~90% of generalized GPA) affecting small vessels with necrotizing granulomatous inflammation of upper/lower respiratory tract plus pauci-immune necrotizing crescentic glomerulonephritis. MPA (microscopic polyangiitis) is p-ANCA (MPO-ANCA) without granulomas.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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