title: Segmental motoneuronal dysfunction is a feature of amyotrophic lateral sclerosis.
abstract: OBJECTIVE
  There is accumulating evidence of dysfunction of spinal circuits in the pathogenesis of amyotrophic lateral sclerosis (ALS).
  
  
  METHODS
  The present study was undertaken to characterise the pathophysiological changes in segmental motoneuronal excitability in 28 ALS patients, using recruitment curves of the soleus H-reflex and M-wave, compared with clinical assessments of upper motor neuron (UMN) and lower motor neuron dysfunction.
  
  
  RESULTS
  H-reflex recruitment curves established that Hmax/Mmax and slope (Hθ/Mθ) ratios predicted clinical UMN dysfunction (p<0.001). Changes in Hθ/Mθ were driven by reduced Mθ. Assessment of Hmax/Mmax was similar in the ALS and control groups, and was affected by overlap of the H and M recruitment curves in ALS patients.
  
  
  CONCLUSIONS
  Changes in the slope ratio (Hθ/Mθ) in ALS suggested that alterations in peripheral motor nerve excitability following UMN damage may affect the recorded H-reflex. Increased collision of reflex discharges with antidromically-conducted motor impulses may be exacerbated in ALS due to preferential loss of large-caliber α-motoneurones, which may explain the similarities in Hmax/Mmax between groups.
  
  
  CONCLUSIONS
  Findings from the present study provide further insight into the pathophysiology of ALS, specifically the relative contributions of premotoneuronal and segmental motoneuronal dysfunction.
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick, NSW 2031, Australia; Prince of Wales Clinical School, University of New South Wales, Randwick, NSW 2031, Australia.
authors.forename: Neil G
authors.initials: NG
authors.lastname: Simon
authors.affiliation: Prince of Wales Clinical School, University of New South Wales, Randwick, NSW 2031, Australia.
authors.forename: Cindy S-Y
authors.initials: CS
authors.lastname: Lin
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick, NSW 2031, Australia.
authors.forename: Michael
authors.initials: M
authors.lastname: Lee
authors.affiliation: Sydney Medical School, K25 - Medical Foundation Building, The University of Sydney, NSW 2006, Australia.
authors.forename: James
authors.initials: J
authors.lastname: Howells
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick, NSW 2031, Australia; Westmead Clinical School, C24 Westmead Hospital, The University of Sydney, NSW 2006, Australia.
authors.forename: Steve
authors.initials: S
authors.lastname: Vucic
authors.affiliation: Sydney Medical School, K25 - Medical Foundation Building, The University of Sydney, NSW 2006, Australia.
authors.forename: David
authors.initials: D
authors.lastname: Burke
authors.affiliation: Neuroscience Research Australia, Barker St, Randwick, NSW 2031, Australia; Brain and Mind Research Institute, The University of Sydney, Mallett St, Camperdown, Australia. Electronic address: matthew.kiernan@sydney.edu.au.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Kiernan
mesh_terms: D000328:Adult; D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000175:diagnosis* / Q000503:physiopathology*; D015331:Cohort Studies; D005260:Female; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009046:Motor Neurons / Q000502:physiology; D018482:Muscle, Skeletal / Q000503:physiopathology; D009431:Neural Conduction / Q000502:physiology
keywords: Amyotrophic lateral sclerosis; H-reflex; Pathophysiology; Segmental motoneurone; Spinal cord circuitry