Spinal excitability changes do not influence the mechanisms of split-hand syndrome in amyotrophic lateral sclerosis.

Abstract

We studied spinal excitability and its relation to motor unit action potential (MUAP) changes in the thenar and hypothenar muscles in patients with amyotrophic lateral sclerosis (ALS). Quantitative MUAP and peak ratio interference analyses were performed, and cutaneous silent period (CutSP) was measured in the abductor digiti minimi (ADM) and first dorsal interosseous (FDI) muscles of patients with ALS and controls. Patients with ALS revealed more prominently increased duration (P = 0.002), number of phases (P = 0.02), size index (P = 0.02), and thickness (P = 0.02) in ADM than in FDI. The number of small segments was significantly decreased in ADM (P = 0.036) compared with controls. CutSP latency was prolonged in both ADM and FDI in ALS (P < 0.05). Although the reinnervation capacity was notably higher in the ADM of patients with ALS, the lack of a significant difference in CutSP measurements between ADM and FDI argues against spinal excitability changes in the development of split-hand syndrome. Muscle Nerve 58: 503-508, 2018.