Muscle biopsy findings predictive of malignancy in rare infiltrative dermatomyositis

ObjectiveThe characteristic pathological muscular findings of polymyositis (PM) and dermatomyositis (DM) have been shown to reflect their different pathogeneses. Here, we characterized the muscle biopsy findings of PM and DM patients with or without malignancy.MethodsWe evaluated the muscle biopsy findings of 215 consecutive PM and DM patients admitted to our hospital between 1970 and 2009. Pathology of the lesion biopsy sections was classified into 3 types: endomysial infiltration-type, perivascular infiltration-type, and rare-infiltrative-type.ResultsThere was no difference between the muscle pathology of PM patients with and without malignancy. However, the incidence of rare-infiltrative type muscle pathology in DM patients with malignancy was significantly higher than in those without such tumors (p = 0.0345).ConclusionThe incidence of rare-infiltrative type muscle pathology may be a predictive marker of DM with malignancy.