Geographical distribution of a seropositive myasthenia gravis population.

INTRODUCTION

To assess age- and sex-specific myasthenia gravis (MG) occurrence and incidence in the different geographical regions in Norway and thereby to identify factors that may contribute to the development of MG.

METHODS

Multiple Poisson regression analysis was used to assess variation in incidence dependent on year, gender and onset age in five geographically defined health regions.

RESULTS

The study population comprised 419 individuals with first time seropositive tests from 1995 to 2007. Annual MG incidence ranged from < 1 to 14 per million, with an average of 7.04 per million for all five health regions combined.

CONCLUSIONS

This is the first nation-wide epidemiological study of seropositive MG that elucidates the geographical differences within a country. The incidence of seropositive MG did not vary significantly between the regions. Mid-Norway tended to have a higher incidence, and North tended to have a lower incidence.