Evoked potential testing in relatives of multiple sclerosis patients.

Evoked potential (EP) tests were obtained in 110 neurologically normal first-degree relatives of patients with multiple sclerosis. Visual EP tests were performed in all relatives; brainstem auditory and median nerve somatosensory EP tests were performed in 67 relatives. The relatives had a mean visual EP P100 latency that was significantly longer than that for normal subjects controlled for age and gender. Asymmetries were seen in results from individual MS relatives, including interocular visual EP P100 differences of up to 14 ms, and interarm somatosensory Erb-N18 differences of up to 3.0 ms. We identified 19 pairs of patients and relatives who were HLA identical and 18 other pairs who were HLA double nonmatched. EP asymmetries were seen more often in the HLA identical siblings than in the HLA double patients, especially if they share HLA types with the patients. Since less than 2% of siblings of MS patients would be expected to eventually develop clinical MS, these small subclinical electrophysiological changes are not expected to be a sign of the future appearance of clinical MS. Clinicians should be aware not to overinterpret small EP changes in relatives of MS patients.