Somatosensory evoked potentials aid in distinguishing primary progressive multiple sclerosis from relapsing forms.

TitleSomatosensory evoked potentials aid in distinguishing primary progressive multiple sclerosis from relapsing forms.
Publication TypeJournal Article
AuthorsKraft GH, McMullen KA
JournalMultiple Sclerosis

Introduction: Prior to the availability of magnetic resonance imaging (MRI), somatosensory evoked potentials (SEPs) were often used in evaluation for multiple sclerosis (MS) to detect a second lesion, thus confirming diagnosis. In recent years, with the widespread availability of MRIs, SEPs are rarely used in MS. We propose that SEPs may aid in distinguishing primary progressive MS (PPMS) from relapsing forms (RFs). Neuropathological studies of RFs and PPMS reveal differences: Whereas relapsing remitting (RR) and secondary progressive (SP) MS are characterized by inflammation and demyelination, PPMS is characterized by axonal degeneration. Because demyelination causes slowing of nerve conduction, our hypothesis was that SEPs could differentiate between RFs and PP MS. Methods: To test this hypothesis, median and tibial SEPs were performed on MS patients whose history clearly categorized them as RR, SP or PP MS. For the purpose of analysis, RFs (RR and SP MS) were grouped together and compared with PPMS. Standardized multi-channel median and tibial SEP testing was performed; latencies, amplitudes, and central conduction (CC) (median: N20 minus N13; tibial: N33 minus N22) were measured. Subjects both early and later in disease stage were studied in both groups. Results: 83 patients (RR/SPMS=53; PPMS=30) were evaluated. Median SEPs did not contribute to the categorization of MS type, likely because of the short path within the central nervous system (CNS). Tibial N33-P37 amplitudes also did not differentiate, as attenuation of signal was often seen in both SP and PP MS. On the other hand, tibial SEP CC showed a distinct difference between types; RFs demonstrated slowing more than PPMS. Normal CC times were shown by almost all (97%) PPMS patients, whereas slow CC times were shown by more than 2/3 (68%) of the RR/SPMS subjects. Using Fisher’s exact test, there was a significant relationship between type of MS (RFs vs. PP) and CC. (p¼0.000) Conclusion: In the clinical setting it is often difficult to distinguish between RFs and PPMS by history alone. Since DMT treatment is effective only in the RFs, disease type clarification is important. Currently, no laboratory test is widely available to distinguish between these 2 forms. This study demonstrates that an available technique, SEPs, can be used to provide useful information to distinguish relapsing forms from primary progressive MS.

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