Juvenile dermatomyositis induced by toxoplasmosis.

A 10-year-old girl from southern Alberta, Canada, who had close contact with cats, developed typical features of dermatomyositis. The diagnosis was confirmed by muscle biopsy. A toxoplasmosis titer was 1:16,384 by indirect fluorescent antibody technique, and the IgM response to toxoplasma was positive. Only minimal improvement followed prednisone and azathioprine administration, but she rapidly improved after 4 weeks of treatment for toxoplasmosis with pyrimethamine and sulfadiazine. A year after the onset of dermatomyositis, she showed no weakness or cutaneous lesions, and a repeat muscle biopsy no longer showed inflammation, perifascicular atrophy, or regeneration of myofibers. She remains asymptomatic more than 2 years after discontinuation of all medications. Investigation for immune deficiency disease 1 year after therapy revealed that lymphocytic response to T-cell and B-cell mitogens was normal, as were immunoglobulin and complement levels. She had mild impairment of natural killer cell activity and a positive antinuclear factor. Her rapid improvement on specific therapy and lack of significant long-term immune deficiency is consistent with acute toxoplasmosis infection in an immunologically competent child.