Abstracts

Rationale: The prevalence of epilepsy in patients with multiple sclerosis (MS) has been of interest for many years, having been reported at between 1% and 10%. Electroencephalography has been of limited value in determining the relationship between the two. To our knowledge, no study so far has focused on the relationship between evoked potentials (EPs) and the presence of epilepsy in MS patients. This study focuses on this relationship, with the hope that this information may help us understand the mechanism of epileptic seizure occurence, both in MS patients and in epilepsy patients in general. Methods: Patients with MS and who have had EPs performed (visual, brainstem and upper and lower limb somatosensory), were retrospectively included. Statistical analyses included the Student t-distribution to determine if the different groups examined differed in patient characteristics such as symptom severity (using the Kurtzke Expanded Disability Status Scale or EDSS), patient age at last follow up, age at symptom onset and time of MS diagnosis. Also, the difference between two proportions with the test statistic z was performed to determine if there were significant differences between the groups based on the percentage of EP abnormalities. Results: One hundred and one patients were retrospectively analyzed. Twenty-seven patients did not have EPs performed and were excluded from further analysis. Seventy-four MS patients included in this study were divided into three groups. I: Patients (n=34) with no epilepsy and not taking anti-epileptic drugs (AED); II: Patients (n=16) with epilepsy and taking AEDs; and III: Patients (n=24) with no epilepsy but taking AEDs for neuropathic pain. No statistically significant difference was found between the groups with regards to symptom severity, age at last follow-up and time since symptom onset and diagnosis. A significant difference in the percentage of patients with upper limb somatosensory EP abnormalities, involving almost exclusively increases in the N/P13-N19 interpeak latency, was found between Groups I (35.5%) and II (63.6%), with an Fz score of 0.95 . No difference between Groups I and III (41.2% for group III, Fz=0.65) and between II and III (Fz=0.87) was found. The Erb's Point-N/P13 interpeak latency was almost always normal, with only one patient showing an absent N/P13 response on one side. The other EPs showed no difference between the groups. Conclusions: Demyelinating lesions involving the upper limb somatosensory pathway, specifically the dorsal/medial aspects of the pathway between the dorsal column nuclei and the ventral posterior nucleus of the thalamus, may be triggering the onset of epilepsy in MS patients. 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 suggests that at least a significant percentage of patients in Group III may potentially have seizures, but are protected as they are taking AEDs for neuropathic pain.