What is polyarteritis nodosa?

• Systemic, necrotizing vasculitis of small and medium-sizedmuscular arteries characteristically involving the renal and visceral arteries. • It spares the smallest blood vessels (arterioles, venules, and capillaries). PAN does not involve pulmonary arteries. • Etiology: Cause not known in the majority of cases. About 30% of patients with PAN have chronic hepatitis B with HBsAg-HbsAb complexes in affected vessels. This indicates an immune complex–mediated etiology in this subset. • Vessels involved: Vessels of the skin, kidneys, heart, liver, peripheral nerves, and gastrointestinal tract.