ADULT-ONSET POLYMYOSITIS DERMATOMYOSITIS - CLINICAL AND LABORATORY FEATURES AND TREATMENT RESPONSE IN 75 PATIENTS

Objectives-To determine possible differences in clinical and laborator y features and treatment response between: patients in Singapore with polymyositis (IM) and dermatomyositis (DM) and reported series. Method s-Case records of adult patients (16 years old and above) referred to the 3 main electromyographic (EMG) laboratories in Singapore between 1 June 1986 and 31 May 1991 were reviewed if the referring diagnosis wa s myositis or myopathy for in investigation. A computer search for adu lt patients with a diagnosis of PM/DM (ICD codes 710.3, 710.4, 517.8) who attended tile main rheumatology and neurology centre during this p eriod was also carried out. The criteria for PM/DM proposed by Bohan a nd Peter was adopted. Results-The incidence of PM/DM was 7.7 cases per million population per year. There were 35 PM and 40 DM cases with a median age at diagnosis of 50.7 years (SD: 16.7) and significantly mor e females in the PM group (p<0.05). At presentation, 86.7% had proxima l myopathy, 34.7% had arthralgia/arthritis and 18.7% had cutaneous vas culitis. The creatine kinase level was elevated in 89.3% of patients a nd positive EMG and muscle biopsy in 79.4% and 76.4% respectively. Sys temic lupus erythematosus was the commonest associated connective tiss ue disease. The percentage of patients with malignancy was higher in D M compared with PM (p<0.01) and they were significantly older (mean ag e 61.8 years) (p<0.001). Patients who achieved remission were signific antly younger (mean age 46.4 years, p<0.05). The overall mortality rat e was 26.7% with infection and malignancy as the main causes of death. Conclusion-The results of the study suggest ethnicity does not influe nce the expression of PM/DM in view of the considerable similarities i n frequency and clinical expression of disease in the population studi ed compared with series from other countries.