title: Distal motor axonal dysfunction in amyotrophic lateral sclerosis.
abstract: Nerve conduction slowing in amyotrophic lateral sclerosis (ALS) is usually caused by loss of fast motor axons. We studied the frequency, extent, and distribution of prominently prolonged distal motor latencies in ALS. We reviewed results of median, ulnar, and tibial nerve conduction studies in 91 patients with ALS, 24 with lower motor neuron disorders, and 36 with axonal neuropathy. Coincidental carpal tunnel syndrome was found for 4 (4.4%) of the ALS patients who were excluded from analyses. Markedly prolonged distal latencies (>125% of the upper limit of normal) were found only in the median nerve of ALS patients (9%), and in none of the disease controls. Excitability studies suggested membrane depolarization in some ALS patients. Our results show that approximately 10% of ALS patients shows prominently prolonged median distal latency, which cannot be explained by axonal loss and carpal tunnel lesion. The distal nerve conduction slowing may partly be caused by membrane depolarization possibly due to motor neuronal degeneration in ALS. We suggest that recognition of the pattern of distal motor axonal dysfunction predominant in the median nerve is clinically important, and could provide additional insights into the pathophysiology of ALS.
authors.affiliation: Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan. y-noto@koto.kpu-m.ac.jp
authors.forename: Yu-ichi
authors.initials: Y
authors.lastname: Noto
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Kanai
authors.forename: Sonoko
authors.initials: S
authors.lastname: Misawa
authors.forename: Kazumoto
authors.initials: K
authors.lastname: Shibuya
authors.forename: Sagiri
authors.initials: S
authors.lastname: Isose
authors.forename: Saiko
authors.initials: S
authors.lastname: Nasu
authors.forename: Yukari
authors.initials: Y
authors.lastname: Sekiguchi
authors.forename: Yumi
authors.initials: Y
authors.lastname: Fujimaki
authors.forename: Masanori
authors.initials: M
authors.lastname: Nakagawa
authors.forename: Satoshi
authors.initials: S
authors.lastname: Kuwabara
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000690:Amyotrophic Lateral Sclerosis / Q000503:physiopathology*; D001369:Axons; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000503:physiopathology; D008875:Middle Aged; D016472:Motor Neuron Disease / Q000503:physiopathology*; D009046:Motor Neurons; D009431:Neural Conduction; D012684:Sensory Thresholds; D013979:Tibial Nerve / Q000503:physiopathology; D014459:Ulnar Nerve / Q000503:physiopathology