[Clinical investigation for polymyositis and related disorders]

The clinical investigation for inflammatory myopathies, which include polymyositis (PM), dermatomyositis (DM) and others, was outlined. The serum creatine kinase (CK) activity increases in the majority of cases of inflammatory myopathies. However, the cases of myositis associated with connective tissue diseases tend to show normal or moderately elevated CK activity. Among the isoenzymes of CK, the MB fraction can increase in the course of treatment as it can originate from regenerating muscle fibres. The macro CK type 1 was reported to appear in association with myositides. Varieties of autoantibodies in the serum such as Jo-1 and Ku have been studied. The Jo-1 antibody is frequently detected in the cases of PM associated with interstitial pulmonary fibrosis. Examination of the heart and lungs is necessary, and so is a search for malignant neoplasms in the cases of DM. Muscle biopsy is mandatory for diagnosing PM, DM and other inflammatory myopathies. Among the latter, inclusion body myositis and granulomatous myopathy need to be identified before treatment as they generally respond poorly. Histological changes of inflammatory myopathies are often distributed unevenly. The magnetic resonance image and ultrasonography are helpful in estimating the distribution of the lesion and therefore in deciding the site of biopsy. Ultrastructural observation of the muscle showed invasion of activated lymphocytes under the basement membrane of the muscle fibres causing degeneration of the myofibrils. The subset analyses of infiltrating cells revealed considerable alterations after the steroid pulse therapy.