Sensory Cortical Hyperexcitability in Amyotrophic Lateral Sclerosis Involves a Broad Hand Representation Within the Primary Somatosensory Cortex

INTRODUCTION/AIMS: Sensory cortical hyperexcitability, reflected by enlarged median nerve somatosensory evoked potentials (SEPs), has been reported in amyotrophic lateral sclerosis (ALS) and is associated with shorter survival. This study investigated whether similar changes involve the ulnar nerve representation within the hand area of the primary somatosensory cortex and examined their relationship with survival. METHODS: Ninety-nine patients with sporadic ALS and 42 healthy controls were retrospectively studied. Sensory nerve action potentials (SNAPs) and SEPs were recorded following median and ulnar nerve stimulation. SNAP amplitudes and the peak-to-peak amplitudes between N20 and P25 (N20p-P25p) were compared between groups. Patients were followed until death or tracheostomy, and associations between SEP amplitudes and survival were analyzed using Kaplan-Meier and Cox proportional hazards analyses. RESULTS: SNAP amplitudes did not differ between patients and controls. In contrast, patients with ALS showed larger N20p-P25p amplitudes for both median and ulnar nerve SEPs. N20p-P25p amplitudes were positively correlated between the two nerves, and the ulnar-to-median amplitude ratio did not differ from controls. Patients with ulnar N20p-P25p ≥ 4.89 μV had significantly shorter survival than those with lower amplitude (log-rank test, p = 0.035). Multivariate Cox analysis identified increased N20p-P25p amplitude as an independent predictor of shorter survival for both nerves. DISCUSSION: Sensory cortical hyperexcitability in ALS extends beyond the median nerve to the ulnar nerve hand area of the somatosensory cortex. Its association with survival supports the notion that sensory cortical dysfunction represents a fundamental pathophysiological feature of ALS and a potential electrophysiological prognostic marker.