Incidence and prevalence of myasthenia gravis in western Denmark: 1975 to 1989.

We studied the epidemiology of myasthenia gravis (MG) in western Denmark from 1975 to 1989, basing case identification on records from all hospitals in the survey area. The population surveyed was 2.80 million in 1985. The average annual incidence rate was 5.0 per million population (women, 5.9; men, 4.2). The point-prevalence rate (January 1, 1990) was 78 per million population (women, 102; men, 53). In men, the incidence increased after 40 years. In women, the incidence rates showed a bimodal pattern with a peak of 7.0 in the age group 20 to 29 years and a second peak of 11.7 in the age group 70 to 79 years. The differences in sex- and age-specific incidence rates suggest that younger women are more susceptible to MG than younger men. Old men and postmenopausal women had similar rates. When last examined, 21% of the 220 prevalent cases were in remission and 18% were moderately or severely disabled.