Background: Autoimmune myasthenia gravis (MG) is a rare neuromuscular transmission disorder. The pathophysiologic mechanisms are well-studied, but the etiology remains unknown. Studies on MG epidemiology report increasing prevalence and incidence of the disease. However, the reported data vary considerably, reflecting differences in study design and case ascertainment. Nationwide population-based cohort studies are rare. Our study provides epidemiological data covering an entire country by utilizing nationwide registries.

Objectives: We aimed to determine the prevalence, incidence and gender specific characteristics of MG patients needing drug treatment in a well-defined population cohort and to assess regional differences in a geographically widespread, but otherwise relatively homogenous population. We also examined the total drug treatment, immune therapy, comorbidity and treatment strategies in MG. Finally we aimed to identify factors that may contribute to exacerbations of MG symptoms.

Methods: Patient information is retrieved from different nationwide registries: The Norwegian Prescription Database (papers I, II and III), the Swedish Prescribed Drug Register (paper III), the Finnish Statistics on Reimbursements for Prescription Medicines (paper III) and the National Patient Register (paper IV).

Results: Our calculated prevalence and incidence is in agreement with other population-based studies. MG patients are more often treated with non-MG prescription drugs than patients using drugs for most other conditions, reflecting frequent co-medication and medical comorbidity. There are age and sex differences in MG medication, reflecting the importance of MG subtypes.