Are somatosensory evoked potentials of the tibial nerve the most sensitive test in diagnosing multiple sclerosis?

Multiple sclerosis (MS) is mostly diagnosed clinically, but the diagnosis has significantly improved through the use of brain magnetic resonance imaging (MRI), testing of cerebrospinal fluid, and multimodal evoked potentials (MEPs). Even though MRI is the superior method in diagnosing this illness, MEPs remain important because they can detect clinically silent lesions in the sensory and motor pathways of the central nervous system (CNS).

The aim of the study is to test the diagnostic sensitivity of MEPs and MRI and the ratio of their sensitivity in patients with MS.

The study subjects included 293 patients with MS with disease duration of two to six years: 249 patients with relapsing-remitting (RR) MS and 44 with primary-progressive (PP) MS. All patients were subjected to an MRI brain scan, visual evoked potentials (VEPs), median somatosensory evoked potentials (SEPs), tibial somatosensory evoked potentials (SEPs), and auditory evoked potentials (AEPs). Abnormal Findings Included : changed wave morphology, interside difference in wave amplitude, absolute and interwave latency increased by 2.5 SD as compared with the control group. The control group comprised of 35 healthy subjects. Results : In this study the most abnormal findings were tibial SEPs, median SEPs, and VEPs. Our results suggest different sensitivity of MEPs in patients suffering from different forms of MS. In RR-MS the sensitivity of tibial SEPs was statically significant (Fischer's exact probability test) as compared to other evoked potential modalities. Similarly VEPs were more sensitive as compared to AEPs. In the PP-MS, median SEPs have been found to be more sensitive than VEPs, while tibial SEPs have been found to be more sensitive than AEPs. There was no significant difference in the sensitivity of MRI and MEPs both the forms of MS.

Tibial SEPs produce the most abnormal results and the highest sensitivity in the RR-MS. We propose that this test as useful criterion for the diagnosis of MS.