A wolf in sheep's clothing

The normal serum creatine kinase and electromyography argued against active polymyositis. Because of these diagnostic uncertainties, we proceeded to open muscle biopsy from right quadriceps. Box 1 Diagnostic criteria for polyarteritis nodosa 7 [black right triangle] Weight loss of >4 kg [black right triangle] Livedo reticularis [black right triangle] Testicular pain [black right triangle] Myalgias, weakness or leg tenderness [black right triangle] Mononeuropathy or polyneuropathy [black right triangle] Hypertension (diastolic blood pressure >90 mm Hg) [black right triangle] Elevated serum urea or creatinine [black right triangle] Presence of hepatitis B surface antigen or antibody arteriographic abnormality [black right triangle] Biopsy of small or medium-sized artery containing polymorphonuclear neutrophils. Positron-emission tomography can help to diagnose large vessel vasculitides, but is usually negative in small-to-medium-sized vessel vasculitis. 8 We considered this patient's muscle scan appearances to have been relevant; the sensitivity of this test in this setting is unknown, although a small study did identify changes on positron-emission tomography in polyarteritis nodosa and other vasculitidies. 9 The main clue in our patient was a very high serum C reactive protein in a phenotype otherwise similar to polymyalgia rheumatica.