Epilepsy and autoimmune diseases: Comorbidity in a national patient cohort

To examine if autoimmune disorders occur with an increased frequency in patients with epilepsy. An autoimmune etiology of epilepsies has been suggested. By using data from The Norwegian Prescription Database (NorPD) we have surveyed a national cohort of patients with active epilepsy treated with antiepileptic drugs.

NorPD contains all prescriptions of drugs dispensed at pharmacies in Norway since 2004. We received data of all drugs prescribed January 2004 - June 2014 for patients receiving an antiepileptic drug.79 751 patients receiving at least two prescriptions of antiepileptic drugs with the reimbursement code for epilepsy were included. To examine autoimmune comorbidity, medications specific for autoimmune diseases were retrieved. Standardized Incidence Ratios (SIR) with 95 % confidence interval (CI) were used to determine whether the occurrence of the prescribed autoimmune drugs in the epilepsy group deviated from the general population. Subgroups stratified for sex and age were examined.

The epilepsy patients were more often treated with insulin and insulin analogs, SIR 1.8 (95 % CI 1.7-1.9); thyroid substitution, SIR 1.7 (95 % CI 1.7-1.8); pyridostigmine, SIR 1.5 (95 % CI 1.1-2.1); multiple sclerosis (MS) medications, SIR 4.9 (95 % CI 4.6-5.3); and immunosuppressive drugs SIR 1.2 (95 % CI 1.1-1.2). All epilepsy subgroups were more often than expected treated with thyroid substitution.

Based on a large, unselected patient cohort we find that epilepsy patients more often are prescribed medications used to treat type 1 diabetes mellitus, hypothyroidism, myasthenia gravis and MS. This was true for both men and women, and in most age-groups.