Prolonged distal latency of the median motor nerve is associated with poor prognosis in amyotrophic lateral sclerosis.

A nerve conduction study (NCS) is routinely undertaken for the differential diagnosis of amyotrophic lateral sclerosis (ALS). Prolonged median motor distal latency (MMDL) has been reported in a subset of patients with ALS. This study aimed to investigate the clinical importance of NCS characteristics in patients with ALS. A total of 75 patients who underwent NCS were enrolled in this study. The frequency of ALS patients with prolonged motor DL was higher in the median than ulnar NCS. The multivariate analysis revealed that shorter diagnostic latency, prolonged MMDL, and higher disease progression rate were significantly associated with poor prognosis. When ALS patients were divided into two groups according to the cut-off value (4.2 ms) of the MMDL, the group with prolonged MMDL had lower ALS functional rating scale and frontal assessment battery scores, upper limbs subscore, and shorter survival time than the group with shorter MMDL. In conclusion, patients with ALS that have prolonged MMDL may have upper limb dysfunction and shorter survival. MMDL can be a useful prognostic marker for patients with ALS.