Myositis as a manifestation of chronic graft-versus-host disease.

We report a 22-year-old man who had myositis in the course of chronic graft-versus-host disease after bone marrow transplantation for acute monocytic leukemia. The distribution of muscular involvement was different from idiopathic polymyositis. Muscular atrophy and weakness were noted in the distal muscles as well as in the proximal muscles of the upper extremities but there was little weakness in the proximal muscles of the lower extremities. However, histological and immunohistochemical study of the biceps brachii muscle showed findings similar to those of idiopathic polymyositis. It was suggested that myositis can be a manifestation of chronic GVHD caused by a cellular immune reaction by donor T cells.