Clinical and pathologic features of focal myositis

To clarify the nosology of focal myositis (FM), we report the clinical and pathologic features of eight patients presenting with focal enlargement of one muscle. Most patients improved without immunosuppressive therapy, and n one developed polymyositis. Pathologic features were those of an inflammato ry myopathy, with muscle fiber hypertrophy and moderate to severe inflammat ion In most cases, a clustering of tightly packed muscle fibers, enveloped by a thick bundle of fibrosis, was associated with the diagnosis of FM. Imm unohistochemistry showed T cell predominance within the interstitial infilt rates in all cases. No evidence of vasculitis was present. Our findings sug gest that FM is a benign condition that has certain clinical features separ ating it from other inflammatory myopathies. Pathologic changes, such as la rge clusters of nesting muscle fibers surrounded by thick fibrosis, are mor e characteristic of FM than polymyositis. (C) 2000 John Wiley & Sons, Inc.