Objective: This study aims to investigate the clinical manifestations and muscular pathological changes of hypomyopathic dermatomyositis (HDM). Methods: A total of 62 patients with dermatomyositis, were enrolled into this study, who underwent muscle biopsy in our hospital between January 2008 and June 2010. Six patients with HDM were screened in accordance with the diagnostic criteria for HDM, in which myogenic damage was found in four patients by EMG. At the same time, biceps brachii biopsies

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... s brachii biopsies were performed in these six patients; and histologi-cal and enzymatic histochemical and immunohistochemical staining were performed for these specimens. The first antibodies for the latter were CD8, CD20 and CD68 mouse anti-human monoclonal antibody and mouse anti-human monoclonal antibody labeled with major histocompatibility complex type-I antigen (MHC-I). Results: Slight to moderate degrees of fat droplets increased in muscular fibers in all six patients, and individual macrophage infiltration and B lymphocytes infiltration appeared in the perimysium. Perifascicular distribution characteristics of individual small round atrophic muscle fibers were found in three patients, accompanied by individual muscle fiber necrosis and regeneration. MHC-I was hyperchromatic in the perifascicular distributed muscle fiber membranes in all patients, and non-specific esterase were hyperchromatic in perifascicular distributed inter-muscular capillaries. Conclusion: Skeletal muscle pathological changes in some patients with HDM were similar to classic dermatomyositis, suggesting that the disease is an intermediate type between amyopathic dermatomyositis and classic dermatomyositis.