Localized nodular myositis.

Two patients presenting with painful, localized swelling in a single muscle are described. Biopsies of involved areas showed inflammatory changes characteristic of polymyositis, but serum levels of muscle-derived enzymes were consistently normal. Both patients later developed evidence of mild diffuse myositis. A review of 4 similar cases in the literature suggests that localized nodular myositis is a heterogeneous condition, in which vascular inflammation may be a prominent feature, with frequent evolution into a generalized myopathy.