Myositis in other connective tissue disorders.

The clinical features, laboratory tests, EMG and muscle biopsy findings are notably similar in many patients with primary and overlap polymyositis. Studies of the immunological abnormalities and immunopathology in both types of inflammatory skeletal muscle conditions are closely related. Thus, there can be little doubt that both primary and overlap myositis are part of the spectrum of autoimmune rheumatic disease. With the recent introduction of monoclonal antibodies that are capable of defining more precisely the cells in a myositis infiltrate, and the development of more refined in vitro tests to study effector cell populations, the precise mechanisms that cause muscle damage are much closer to being identified.