Abstracts

Rationale: The prevalence of epilepsy in patients with multiple sclerosis (MS) has been of interest for many years, having been reported at 1 to 10%. Electroencephalography (EEG) has been of limited value in determining the relationship between the two, with the EEG being abnormal in only about two thirds of cases, and in which slow waves rather than spikes are seen. Evoked potentials are an alternative electrophysiological evaluation that may provide answers as to why some MS patients and not others develop epilepsy. This analysis focuses on the relationship of evoked potential abnormalities and epilepsy in MS patients. Methods: Patients with MS who have had evoked potentials (EPs) performed (visual, brainstem (BAEP) and upper (USSEP) and lower limb somatosensory) were retrospectively included. Results: Two hundred and eighteen MS patients were divided into three groups. I: Patients (n=148) with no epilepsy and not taking anti-epileptic drugs (AED); II: Patients (n=17) with epilepsy and taking AEDs; and III: Patients (n=53) with no epilepsy but taking AEDs for neuropathic pain. A significant difference in the percentage of patients with brainstem auditory EP abnormalities was found between Groups I (15.0%) and II (33.3%), with an Fz score of 0.96. No difference between Groups I and III and between II and III was found. The USSEP showed borderline significance between groups I and II (Fz=0.93) and between groups II and III (Fz=0.95). The other EPs showed no difference between the groups. Statistically significant differences were found however with respect to time since onset of symptoms and EDSS scores between groups I and II and between groups I and III. These latter findings however do not parallel the BAEP and USSEP findings. Conclusions: There appears to be preferential involvement of BAEPs and USSEPs in MS patients with epilepsy. Possible confounding factors of AED use were ruled out by the comparison between Groups I and III. However, the similarity between Groups II and III with regards to the BAEP suggests that the latter patients may potentially have seizures, but are protected as they are taking AEDs for neuropathic pain. Studies in MS and epilepsy patients in the past using MRI has not indicated any preferential location of demyelinating lesions either in relation to the USSEP(medial lemniscus/somatosensory cortex) or BAEP (pons to midbrain) pathways. A review of the literature shows that the substantial nigra has been implicated in the control of epilepsy, lesions in which result in the suppression of epilepsy. The substantia nigra (SN) receives afferents from the subthalamic nucleus (STN). The BAEP and USSEP have been shown to be recorded from the STN, and lesions in the STN alter the USSEP recording. We hypothesis that the preferential involvement of the BAEP and USSEP may be due to demyelinating lesions in the STN, resulting in the activation of the SN and the presence of epilepsy.