Polyarteritis nodosa presenting as polymyositis

Skeletal muscle involvement has been well documented in patients with polyarteritis nodosa (PAN), and symptoms referable to skeletal muscle are not uncommon. However, polymyositis as a mode of presentation of PAN is uncommon. This unusual presentation of PAN has been reported only once previously in the English literature.

This study describes a patient who had diffuse weakness, myalgias, and markedly elevated serum creatinine phosphokinase, mimicking polymyositis. The literature dealing with the clinical aspects of muscle involvement in PAN is reviewed.

A 24-year-old man was admitted to the hospital with a 1-month history of fever, myalgia, and muscle weakness. Necrotizing vasculitis was shown on subsequent muscle biopsy, consistent with PAN. Literature review indicated that muscle involvement is common in PAN, as has been shown by the frequency of muscular symptoms and by histologic evidence obtained from both clinical and autopsy studies. Nineteen percent of patients with PAN had documented myopathy, and autopsy series have shown skeletal muscle involvement in 30% to 48% of cases. However, polymyositis as a mode of presentation of PAN is rare. We found only 1 other patient with PAN who had elevated creatinine phosphokinase and diffuse myopathy suggestive of polymyositis.

PAN should be suspected in cases of focal or diffuse myopathy, especially in the context of a systemic disease. Biopsy of symptomatic muscles or EMG-directed biopsies can be helpful in establishing a diagnosis of PAN to allow the physician to provide early treatment.