Multiple sclerosis and seizures: incidence and prevalence over 40 years.

OBJECTIVES: The prevalence of multiple sclerosis (MS) is increasing worldwide. Epileptic seizures are more common in MS patients than in the general population. The aim of this study was to investigate changes in the prevalence and incidence of MS in a well-defined population over several decades and estimate the occurrence of epilepsy in the same cohort. MATERIALS AND METHODS: Patients diagnosed with MS in the County of Vestfold, Norway in the period of 1983-2003 were identified. Point prevalence for MS and epilepsy was calculated for January 1, 2003. The average annual incidence rates were calculated in five-year periods from 1983 to 2002. These numbers were compared to previously published figures of prevalence from 1963 and incidence from 1953. RESULTS: On prevalence day, we identified 364 patients diagnosed with MS living in Vestfold. Thus, the prevalence increased from 61.6/100,000 in 1963 to 166.8/100,000 in 2003. In the period 1983-2002, the annual incidence fluctuated between 4.2 and 7.3/100,000/year (mean 4.5, 95% CI 3.6 - 5.5). In 2003, the portion of MS patients with epileptic seizures was 7.4%, compared to 2.9% in 1963. CONCLUSIONS: During the 40 years follow-up of this population, the incidence of MS was stable, while the prevalence of MS and the share of MS patients with epileptic seizures increased. Compared to the general population, the risk of having active epilepsy was increased fourfold. We assume that this is a consequence of an increased survival in MS patients.