Upper limb motor evoked potentials as outcome measure in progressive multiple sclerosis

Objective: To assess the usefulness of upper limb (UE) motor evoked potential (MEPs) as a marker of motor impairment in a cohort of people with progressive multiple sclerosis (PwPMS).

Methods: we evaluated UE and lower extremities (LE) MEPs, 6-minutes walk-test (6MWT), 10-meter walk-test (10MWT), EDSS, 9-hole peg-test (9HPT), and measures of strength (MRC) and tone (MAS) to the UE and LE in 50 PwPMS (EDSS 4.0-6.5; P ≥ 3, C ≤ 2).

Results: Bilateral absence of LE-MEPs, found in 74% of cases, was associated with worse 10MWT and 6MWT. UE-MEPs were rarely absent (8%) but often delayed (74%). Abnormal UE-MEPs were associated with worse performance at 9HPT (25.8 vs 33.2 s). UE-MEPs latency correlated with 10MWT (rho = 0.597), 6MWT (rho = -0.425) and EDSS (rho = 0.296).

Conclusion: UE-MEPs may represent a clinically relevant outcome measure to quantify corticospinal tract integrity in PwPMS, at least when LE-MEPs cannot provide a measurable response.

Significance: The strive for novel remyelination strategies in MS points to the need for quantitative conduction measurements in addition to clinical outcomes. The frequent absence of MEPs to the lower limbs in PwPMS may greatly limits their usefulness in monitoring progression or response to therapies. With this respect, the upper extremities may represent a better target.