title: Prominent fatigue in spinal muscular atrophy and spinal and bulbar muscular atrophy: evidence of activity-dependent conduction block.
abstract: OBJECTIVE
  To clarify whether patients with spinal muscular atrophy (SMA) or spinal and bulbar muscular atrophy (SBMA) suffer disabling muscle fatigue, and whether activity-dependent conduction block (ADCB) contributes to their fatigue. ADCB is usually caused by reduced safety factor for impulse transmission in demyelinating diseases, whereas markedly increased axonal branching associated with collateral sprouting may reduce the safety factor in chronic lower motor neuron disorders.
  
  
  METHODS
  We assessed the fatigue severity scale (FSS) in 22 patients with SMA/SBMA, and in 100 disease controls (multiple sclerosis, myasthenia gravis, chronic inflammatory demyelinating polyneuropathy (CIDP), and axonal neuropathy). We then performed stimulated-single fibre electromyography (s-SFEMG) in the extensor digitorum communis (EDC) muscle of 21 SMA/SBMA patients, 6 CIDP patients, and 10 normal subjects.
  
  
  RESULTS
  The FSS score was the highest in SMA/SBMA patients [4.9 ± 1.1 (mean ± SD)], with 81% of them complaining of disabling fatigue, compared with normal controls (3.5 ± 1.0), whereas patients with multiple sclerosis (4.3 ± 1.6), myasthenia gravis (4.0 ± 1.6) or CIDP (4.3 ± 1.4) also showed higher FSS score. When 2000 stimuli were delivered at 20 Hz in s-SFEMG, conduction block of single motor axons developed in 46% of patients with SMA/SBMA, and 40% of CIDP patients, but in none of the normal controls.
  
  
  CONCLUSIONS
  SMA/SBMA patients frequently suffer from disabling fatigue presumably caused by ADCB induced by voluntary activity.
  
  
  CONCLUSIONS
  ADCB could be the mechanism for muscle fatigue in chronic lower motor neuron diseases.
authors: Department of Neurology, Graduate School of Medicine, Chiba University, Chiba, Japan. y-noto@koto.kpu-m.ac.jp
authors: Yu-ichi
authors: Y
authors: Noto
authors: Sonoko
authors: S
authors: Misawa
authors: Masahiro
authors: M
authors: Mori
authors: Naoki
authors: N
authors: Kawaguchi
authors: Kazuaki
authors: K
authors: Kanai
authors: Kazumoto
authors: K
authors: Shibuya
authors: Sagiri
authors: S
authors: Isose
authors: Saiko
authors: S
authors: Nasu
authors: Yukari
authors: Y
authors: Sekiguchi
authors: Minako
authors: M
authors: Beppu
authors: Shigeki
authors: S
authors: Ohmori
authors: Masanori
authors: M
authors: Nakagawa
authors: Satoshi
authors: S
authors: Kuwabara
mesh_terms: D000200:Action Potentials; D000328:Adult; D000368:Aged; D001369:Axons / Q000502:physiology; D004576:Electromyography; D005221:Fatigue / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D009068:Movement / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D018908:Muscle Weakness / Q000209:etiology* / Q000503:physiopathology; D009134:Muscular Atrophy, Spinal / Q000150:complications* / Q000503:physiopathology*; D020966:Muscular Disorders, Atrophic / Q000150:complications* / Q000503:physiopathology*; D009431:Neural Conduction / Q000502:physiology; D055815:Young Adult
keywords: Activity-dependent conduction block; Chronic inflammatory demyelinating polyneuropathy; Fatigue; Spinal and bulbar muscular atrophy; Spinal muscular atrophy; Stimulated-single fiber electromyography