title: Increased variability of axonal excitability in amyotrophic lateral sclerosis.
abstract: OBJECTIVE
  Amyotrophic lateral sclerosis (ALS) is characterised by the increased excitability of motoneurons and heterogeneous loss of axons. The heterogeneous nature of the disease process among fibres may show variability of excitability in ALS.
  
  
  METHODS
  Multiple nerve excitability tests were performed in 28 ALS patients and 23 control subjects, by tracking at the varying threshold levels (10%, 20%, 40% and 60% of maximum amplitudes).
  
  
  RESULTS
  In normal controls, excitability measures at low target levels have the following characteristics compared to those at high target levels: longer strength-duration time constant, greater threshold reduction during depolarising currents and smaller threshold increase to hyperpolarising currents. ALS patients had less clear amplitude dependency of the parameters than the controls, indicating variability of axonal excitability. Three ALS patients demonstrated greater target-amplitude-dependent threshold changes in threshold electrotonus than controls, suggesting selective axonal hyperexcitability.
  
  
  CONCLUSIONS
  Some of the ALS patients had variable axonal excitability at different target amplitudes, suggesting preferential hyperexcitability in the axons with low target amplitude levels.
  
  
  CONCLUSIONS
  Variable membrane potentials of motor axons in ALS may be assessed by recording excitability testing at different target amplitude levels.
authors.affiliation: Department of Neurology, Tokushima University, Tokushima, Japan.
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Shibuta
authors.forename: Yoshimitsu
authors.initials: Y
authors.lastname: Shimatani
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nodera
authors.forename: Yuishin
authors.initials: Y
authors.lastname: Izumi
authors.forename: Ryuji
authors.initials: R
authors.lastname: Kaji
mesh_terms: D000200:Action Potentials; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000690:Amyotrophic Lateral Sclerosis / Q000503:physiopathology*; D001369:Axons / Q000502:physiology*; D004056:Differential Threshold; D054351:Electrical Synapses / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008564:Membrane Potentials; D008875:Middle Aged; D008959:Models, Neurological; D009046:Motor Neurons / Q000502:physiology; D013997:Time Factors
keywords: ALS; CMAP; Depolarisation; I/V; Membrane potential; RC; RRP; SDTC; SNAP; SR; TE; Threshold electrotonus; amyotrophic lateral sclerosis; compound muscle action potential; current–threshold relationship; recovery cycle; relative refractory period; sensory nerve action potential; stimulus–response; strength–duration time constant; threshold electrotonus