RESUMEN
We describe a 28-year old man in otherwise apparently good health, in whom pain in his left knee joint caused by avascular necrosis led to a diagnosis of polyarteritis nodosa (PAN). The angiogram showed multiple microaneurysmal and thrombotic lesions, notably in the renal, mesenteric and tibial arteries. A skin biopsy of the upper dermis of the left thigh with an erythematous skin rash showed the infiltration of mononuclear leukocytes in the perivascular area. During hospitalization, he was diagnosed with chronic hepatitis B, and was treated with lamivudine, and corticosteroid, azathioprine to control the PAN. The knee joint pain improved progressively, and the patient could walk normally after several months. This case is an unusual presentation because the initial manifestation of PAN was avascular necrosis.