Offset Conduction Velocity Reveals Prognostic Slowing of Motor Axons in Amyotrophic Lateral Sclerosis

INTRODUCTION/AIMS: Slowing of motor nerve conduction is not classically regarded as a feature of amyotrophic lateral sclerosis (ALS). We introduce a novel electrophysiological parameter, offset motor conduction velocity (offset-MCV), to assess conduction in relatively slower motor axons and investigate its association with survival in ALS. METHODS: Motor nerve conduction studies of the median and tibial nerves were performed in 145 patients with ALS and 70 healthy controls. Onset and offset latencies of compound muscle action potentials were measured, and onset- and offset-MCVs were calculated. Patients were followed until death or tracheostomy, and associations between MCV parameters and survival were analyzed. RESULTS: Both onset- and offset-MCVs were significantly reduced in patients with ALS compared with controls for the median and tibial nerves (all p < 0.0001). Onset-MCVs were not associated with survival. In contrast, reduced offset-MCVs in both nerves were associated with short survival (log-rank test: median nerve, p = 0.009; tibial nerve, p = 0.021). Multivariate Cox regression analysis identified tibial nerve offset-MCV as an independent prognostic factor (p = 0.029). DISCUSSION: Pathological slowing of motor nerve conduction occurs in ALS and is associated with poor survival. Offset-MCV may reflect disease-related changes in slower α-motor axons and represents a potential prognostic biomarker in ALS.