Dermatomyositis as an immunologic complication of toxoplasmosis.

We present immunohistochemical, light- and electron-microscopic findings on a muscle biopsy specimen from a 21-year-old woman who developed debilitating dermatomyosisits in the course of toxoplasmosis. The muscle showed perifascicular muscle cell atrophy and prominent ultrastructural changes consistent with polymyositis. These myopathic changes were interpreted as an immunologic complication of systemic toxoplasmosis and were related to immunohistochemically demonstrable immune complex deposits in the small blood vessels. Our data suggest that dermatomyositis is caused and/or related to Toxoplasma infection and is an immune complex-mediated systemic disease.