FOCAL MYOSITIS - A CLINICOPATHOLOGICAL STUDY

Focal myositis is a rare, benign inflammatory condition that may clini cally simulate a soft tissue sarcoma. It was first described in 1977 a nd around 30 cases have been reported to date. We report two further c ases on which we have performed immunocytochemistry and electron micro scopy. Histology of both lesions was identical, showing a destructive inflammatory myopathy with evidence of regeneration. Stains for micro- organisms were negative and no viral particles were seen on electron m icroscopy. The immunocytochemical profile of our two cases differed fr om that of polymyositis: with a panel of T- and B-cell markers the cel lular infiltrate was found to be composed of T-lymphocytes and variabl e numbers of macrophages: sub-typing in one case revealed the T-cells to be predominantly CD4+ cells. Use of antibodies to MHC class 1 and 2 antigens showed occasional positive inflammatory cells only. Clinicop athological correlations and the differential diagnosis are discussed.