[Epidemiology of myasthenia gravis]

Abstract

Myasthenia gravis (MG) is an organ-specific autoimmune disorder characterized by weakness and fatigue of voluntary muscles, and presence of autoantibodies to acetylcholine receptor of postsynaptic muscle membrane. A review of the international literature suggests that there is large variety of MG frequency and distribution. An annual incidence rate of MG is thought to be between 0.25 and 20 per 1,000,000 population. The prevalence of MG in world shows even wider variation, i.e. ranging from 50/1,000,000 in Hong Kong to 200/1,000,000 in Virginia (USA). Among population of Belgrade, an average annual incidence rate during the period 1983-1992 was 7.1/1,000,000, and prevalence on December 31, 1992 was 121.5/1,000,000. The mortality rate of MG is very low with value under 1/1,000,000. Epidemiological studies of MG have indicated trend of increasing MG prevalence with relatively stable incidence. This reflects the impact of effective treatment, improved diagnostic methods and prolonged survival. Due to development of intensive care facilities and immunomodulating treatment, the mortality of MG has significantly decreased. The most common age of MG onset is between 20 and 40 years. In this age group, about 60% of patients are women, while sex ratio at older age is 1:1. Stressful life events, viral infections, pregnancy and delivery may precipitate the development of MG. MG is associated with other autoimmune diseases in about 30% of cases. Although the number of patients with MG continues to rise, it is still a rare disease. Further epidemiological research with a view to establish population registries and to estimate economic impact of disease on population as well as quality of life of patients with MG is needed.