Occurrence of polymyositis in the county of Gävleborg, Sweden.

Through register research 21 new cases (10 male, 11 female) of polymyositis/dermatomyositis during the period 1984-1993 in the county of Gävleborg, Sweden, were identified. The case records were studied retrospectively. Inclusion body myositis was found in three cases and overlap syndrome in seven cases. Three patients had associated malignant disease. The annual incidence was estimated to 7.6 cases/million people. The clinical features are described. 19 patients were given steroid treatment, and azathioprin was the most used additive immunosuppressive drug. All patients could be followed for at least two years, and during this period three patients died (all of cancer disease). Remission and withdrawal of medication were achieved in five cases. The results of the study corresponds to previous investigations with similar design.