Granulomatous myositis - Clinicopathologic study of 12 cases

Granulomatous inflammation is infrequently encountered in skeletal muscle b iopsy material. Of 2,985 muscle biopsy specimens reviewed over 12 years, 12 (0.4%) birth granulomatous inflammation were identified. The patients incl uded 9 women who ranged in age from 24 to 76 years (mean 50.3 years). The m ost common clinical findings included decreased strength or weakness in the extremities (n = 8), muscle pain (n = 5), and weight loss (n = 3). All mus cles exhibited nonnecrotizing granulomas; an associated vasculitic process tl las identified in 2. Endomysial chronic inflammation consisting primaril y of lymphocytes and plasma cells was present in 10 muscles, and perivascul ar chronic inflammation in 8. Degenerating muscle fibers were noted in 10 c ases, and regenerating fibers in 11. Evidence of neurogenic atrophy was see n in 8 muscles. Increased endomysial fibrosis was observed in 5 muscles, an d type II muscle fiber atrophy in 5 muscles. Stains for acid-fast bacilli a nd Gomori methenamine silver stain were performed in all but 2 cases and fa iled to demonstrate organisms. In 3 cases, concomitant sural nerve biopsies were performed, and granulomas were identified in 2 of those cases. Clinic oparhologic diagnoses included sarcoidosis (n = 6), vasculitis (n = 2), and granulomatous myositis not otherwise specified (n = 2). In 2 cases, there was insufficient clinical information or follow-up darn to determine a caus e. In conclusion, granulomatous myositis is infrequently found in muscle bi opsy specimens (0.5% of all biopsies in this series); most muscles demonstr ate evidence of chronic endomysial or perivascular inflammation accompanied by muscle fiber degeneration and regeneration; and the most common cause f or granulomatous myositis was sarcoidosis in this series.