A previous epidemiological study on myasthenia gravis (MG) in Sardinia indicated a prevalence rate of 4.5 per 100,000 population and an incidence of 0.25 per 100,000 population in the period 1958–1986. This study, however, investigated the entire Sardinian population (about 1,500,000) and the reported rates are likely to be underestimated. Because the use of a very large population has been found to cause major bias in case finding, the present study was designed to overcome this bias by determining the prevalence and incidence of MG in a well-defined area of Northwestern Sardinia, with a population of about 270,000 (1991 census). Potential MG cases were ascertained using all possible medical sources. The diagnosis of MG was based on the clinical, neurophysiological and conventional pharmacological findings (Tensilon test, response to anticholinesterases). On prevalence day (December 31, 1994) 29 MG patients were living in the study area (17 women and 12 men). Since the total population on prevalence day was 268,926 (137,284 women and 131,642 men), the calculated prevalence was 11.1 per 100,000 population (12.4 women and 9.9 men). The present study shows that the risk of MG in Sardinia is higher than previously suggested. The risk, however, is not significantly different from that found in other comparable Italian and European areas. It contrasts with what has been found for other autoimmune diseases such as multiple sclerosis and insulin-dependent diabetes mellitus in Sardinians, both showing frequencies up to 3–5 times higher than in the rest of It
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