Classification and prognosis of inflammatory muscle disease

Although our understanding of the inflammatory myopathies is still evolving, it is becoming increasingly clear that these syndromes are composed of many separate and distinct disorders with widely divergent clinical signs, symptoms, laboratory abnormalities, and prognoses. Their classification remains controversial, but three approaches of dividing the myositis syndromes appear useful in helping to group disorders with similar features together. The three approaches divide these syndromes on the basis of clinical and histopathologic findings, by serology, and by exposures to known environmental agents. Studies of the prognosis of these disorders are limited by the rarity and heterogeneity of the myositis syndromes. Taken together, however, they suggest that a variety of demographic, clinical, and serologic features are associated with a poor outcome. These include older age at myositis onset, severe myositis, delay to diagnosis and therapy, significant cardiac, pulmonary or gastrointestinal involvement, and the presence of cancer, inclusion body myositis, or antisynthetase or anti-SRP auto-antibodies. It is hoped that our understanding of the classification and prognosis of the inflammatory myopathies will become more complete as we perceive more fully the interrelationships between the genetic and environmental risk factors necessary for the induction of myositis and develop more rational ways of dividing and treating these increasingly recognized syndromes.