MORTALITY AND SURVIVAL IN MYASTHENIA-GRAVIS - A DANISH POPULATION-BASED STUDY

Objectives-To study mortality and survival of patients with myasthenia gravis.Methods-290 patients with myasthenia gravis were studied, incl uding 212 incident cases identified during a comprehensive epidemiolog ical study of myasthenia gravis in western Denmark 1975-89. Follow up was performed on 31 December 1994. Survival curves were constructed us ing the life table method. Patient data were compared with data from t he public Danish population statistics. Death certificates were provid ed from the National Registry of Death. Results-The annual average cru de mortality rate was 1.8 per million (range 1.5-2.2). The myasthenia gravis related mortality rate (myasthenia gravis as underlying or cont ributory cause) was 1.4 per million (range 1.1-1.8). The age specific mortality rates were low below 50 years. After this age the mortality increased with age in both sexes; after 60 years more rapidly in men t han in women. The overall survival rates three, five, 10, and 20 years from diagnosis were 85%, 81%, 69%, and 63% respectively. The survival of both sexes was shorter than that of the corresponding Danish popul ation. Old age at diagnosis, a classification in Osserman-Genkins grou p IIB or III, and the presence of a thymoma were associated with a les s favourable prognosis. The three, five, 10, and 20 year survival rate s of thymectomised patients were 94%, 94%, 86%, and 79% respectively. The corresponding figures for the non-thymectomised patients were 78%, 71%, 56%, and 51%. A Cox regression analysis showed that this apparen tly significant effect of thymectomy was because the thymectomised pat ients were younger than the non-thymectomised patients. Furthermore, a t the time of diagnosis of myasthenia gravis the non-thymectomised pat ients had a higher frequency of serious conditions associated with mya sthenia gravis than the thymectomised patients. Conclusion-Patients wi th myasthenia gravis generally have a relative good prognosis although their survival is shorter than that of the corresponding population. Old age, a classification in Osserman-Genkins group III, and the prese nce of a thymoma are associated with a less favourable prognosis. In t his study, the apparently significant effect of thymectomy was because the thymectomised patients were younger than non-thymectomised patien ts and because the non-thymectomised patients had a higher frequency o f serious conditions associated with myasthenia gravis.