Chronic myositis with cardiomyopathy and respiratory failure associated with mild form of organ-specific autoimmune diseases.

We report the four patients with chronic myositis characterized by a very slow progression with cardiomyopathy and frequently with marked respiratory muscle weakness associated with other organ-specific autoimmune diseases such as primary biliary cirrhosis. The histopathology of the muscle showed many degenerative and regenerative fibers, but inflammatory-cell infiltration were minimal. The patients showed favorable response to high-dose corticosteroid treatment. Because of these clinical features, these patients are sometimes misdiagnosed as muscular dystrophy and not treated properly. It is important to distinguish this type of treatable myositis.