Epilepsy in multiple sclerosis: A nationwide population-based register study.

OBJECTIVE: To determine the cumulative incidence of epilepsy in a population-based cohort of patients with multiple sclerosis (MS) and to investigate the association between epilepsy and clinical features of MS.

METHODS: All available patients in the Swedish MS register (n = 14,545) and 3 age- and sex-matched controls per patient randomly selected from the population register (n = 43,635) were included. Data on clinical features of MS were retrieved from the Swedish MS register, and data on epilepsy and death were retrieved from comprehensive patient registers.

RESULTS: The cumulative incidence of epilepsy was 3.5% (95% confidence interval [CI] 3.17-3.76) in patients with MS and 1.4% (95% CI 1.30-1.52) in controls (risk ratio 2.5, 95% CI 2.19-2.76). In a Cox proportional model, MS increased the risk of epilepsy (hazard ratio 3.2, 95% CI 2.64-3.94). Patients with relapsing-remitting MS had a cumulative incidence of epilepsy of 2.2% (95% CI 1.88-2.50), whereas patients with progressive disease had a cumulative incidence of 5.5% (95% CI 4.89-6.09). The cumulative incidence rose continuously with increasing disease duration to 5.9% (95% CI 4.90-7.20) in patients with disease duration ≥34 years. Patients with an Expanded Disability Status Scale (EDSS) score ≥7 had a cumulative incidence of epilepsy of 5.3% (95% CI 3.95-7.00). Disease duration and EDSS score were associated with epilepsy after multiple logistic regression (odds ratio [OR] 1.03, 95% CI 1.01-1.04 per year, p = 0.001; and OR 1.2, 95% CI 1.09-1.26 per EDSS step, p < 0.0001).

CONCLUSIONS: Epilepsy is more common among patients with MS than in the general population, and a diagnosis of MS increases the risk of epilepsy. Our data suggest a direct link between severity of MS and epilepsy.