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

ABSTRACT

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.

Abbreviations: ADM = abductor digiti minimi; APB = abductor pollicis brevis; ALS = amyotrophic lateral sclerosis; ALSFRS-R = revised ALS Functional Rating Scale; CI = confidence interval; CMAP = compound muscle action potential; CTS = carpal tunnel syndrome; DL = distal latency; ΔFS = disease progression rate; FAB = frontal assessment battery; FVC = forced vital capacity; HR = hazard ratio; MCV = motor nerve conduction velocity; MMDL = median motor distal latency; MMSE = mini-mental state examination; NCS = nerve conduction study; PaCO₂ = partial pressure of arterial carbon dioxide; SBMA = spinal and bulbar muscular atrophy; SCV = sensory nerve conduction velocity; SD = standard deviation; SMA = spinal muscular atrophy; SNAP = sensory nerve action potential; SOD1 = superoxide dismutase 1; UMDL = ulnar motor distal latency.

KEYWORDS:

• Amyotrophic lateral sclerosis
• median nerve
• distal latency
• disease progression rate
• prognosis

Acknowledgments

The authors thank all patients for their participation in this study. This study was supported in part by Grants-in-Aid for Scientific Research (C) (19K07813 to Y.I.) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

Disclosure statement

The authors report that they have no conflicts of interest.

Additional information

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Notes on contributors

Yoshio Ikeda

Masayuki Sato is a Ph.D. student at Gunma University Graduate School of Medicine in the Department of Neurology. He received his M.D. from Hirosaki University in 2011.

Takumi Nakamura is a clinical fellow in the Department of Neurology, Gunma University Graduate School of Medicine. His interest is especially clinical studies on neurodegenerative disorders.

Kazuaki Nagashima is a research associate in the Department of Neurology, Gunma University Graduate School of Medicine. His interest is especially clinical studies on amyotrophic lateral sclerosis.

Yukio Fujita is an assistant professor in the Department of Neurology, Gunma University Graduate School of Medicine. His interest is especially neuropathological studies on amyotrophic lateral sclerosis.

Yoshio Ikeda is a professor in the Department of Neurology, Gunma University Graduate School of Medicine. He has focused mainly on molecular pathological and clinical studies on neurodegenerative disorders.