Prevalence rates of myasthenia gravis. Prevalence rate (PR) is shown in cases per million persons with 95% confidence intervals (95% C.I.) according to the Poisson distribution and weighting according to the random effects model. All MG ePR = 77.67 cases per million (C.I.: 63.98, 94.30), range = 15 to 179 cases per million; AChR MG: range = 70.6 to 163.5; MuSK range = 1.9-2.9.