Clinical meaning
Polyarteritis nodosa (PAN) is a systemic necrotizing vasculitis affecting medium-sized muscular arteries, causing segmental transmural inflammation with fibrinoid necrosis of the vessel wall, aneurysm formation, thrombosis, and downstream organ ischemia. Unlike ANCA-associated vasculitides, PAN is ANCA-negative and does NOT involve small vessels or glomerulonephritis (spares the lungs and glomeruli). The inflammation is immune complex-mediated, with approximately 30% of cases associated with hepatitis B virus (HBV) infection. Affected organs include kidneys (renal artery aneurysms causing renovascular hypertension, NOT glomerulonephritis), gastrointestinal tract (mesenteric artery involvement causing postprandial abdominal pain and bowel ischemia), peripheral nervous system (vasa nervorum inflammation causing mononeuritis multiplex), skin (livedo reticularis, subcutaneous nodules, ulcers), and musculoskeletal system (myalgias, arthralgias). Constitutional symptoms include fever, weight loss, and malaise.