Clinical and serologic features of patients with polymyositis or dermatomyositis

The clinical and serologic features of 36 patients with polymyositis (PM) or dermatomyositis (DM) were observed over a 5-year period. The mean age of the patients at the time of diagnosis was 48.5 years, and 61% were female. According to widely accepted diagnostic criteria 50% had PM (group I), 14% DM (group II), 11% PM or DM associated with malignant disease (group III) and 25% PM or DM associated with a connective tissue disorder (group V). None of the patients had childhood PM or DM associated with vasculitis (group IV). All the patients had muscle weakness, and 94% of the patients tested had an elevated serum level of creatine kinase. The average delay from the onset of symptoms to diagnosis was 14 months overall but only 2.3 months for the DM patients. Of the 30 patients whose serum was tested, 73% had antinuclear antibodies, with antibodies to nuclear ribonucleoprotein being most common in group V patients and antibodies directed against the Jo-1 antigen being restricted to patients with PM alone (group I).