title: Increased supernormality in patients with multiplet discharges: Evidence for a common pathophysiological mechanism behind multiplets and fasciculations.
abstract: OBJECTIVE
  To determine whether there is a relation between electrically evoked multiplet discharges (MDs) and motor axonal excitability properties. We hypothesized that electrically evoked MDs share their underlying pathophysiological mechanism with fasciculations.
  
  
  METHODS
  High-density surface EMG and motor nerve excitability recordings of the thenar muscles were performed in 22 patients with motor neuron disease (MND) in their differential diagnosis and who were referred for EMG examination.
  
  
  RESULTS
  Supernormality (hyperexcitable phase following the refractory period) was significantly increased in patients with MDs (n=10) compared to patients without MDs (n=12) (25.5% vs 17.0%; p=0.02). Depolarizing threshold electrotonus differed significantly between both groups as well (TEdpeak, 76.6% vs 66.6%, p<0.01; TEd90-100ms, 51.7% vs 44.3%, p<0.01) CONCLUSIONS: Our findings imply that the same pathophysiological excitability changes are involved in generating MDs and fasciculations. Yet, MDs may be quantified more easily, and may be more specific for abnormal distal excitability than fasciculations, because fasciculations may originate along the motor axon as well as in the neuron cell body.
  
  
  CONCLUSIONS
  MDs are potentially useful as objective measure of increased distal axonal excitability at individual motor unit level and might complement clinical studies in MND.
authors.affiliation: Department of Clinical Neurophysiology, The Netherlands. Electronic address: b.sleutjes@erasmusmc.nl.
authors.forename: Boudewijn T H M
authors.initials: BT
authors.lastname: Sleutjes
authors.affiliation: Department of Clinical Neurophysiology, The Netherlands.
authors.forename: Inger
authors.initials: I
authors.lastname: Montfoort
authors.affiliation: Department of Neurology, Erasmus MC, University Medical Centre Rotterdam, The Netherlands.
authors.forename: Pieter A
authors.initials: PA
authors.lastname: van Doorn
authors.affiliation: Department of Clinical Neurophysiology, The Netherlands; Department of Clinical Neurophysiology, SEIN Heemstede, The Netherlands.
authors.forename: Gerhard H
authors.initials: GH
authors.lastname: Visser
authors.affiliation: Department of Clinical Neurophysiology, The Netherlands; Department of Clinical Physics, Reinier de Graaf Hospital Delft, The Netherlands.
authors.forename: Joleen H
authors.initials: JH
authors.lastname: Blok
mesh_terms: D000328:Adult; D000368:Aged; D001369:Axons / Q000502:physiology; D003937:Diagnosis, Differential; D004576:Electromyography; D005071:Evoked Potentials / Q000502:physiology*; D005207:Fasciculation / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016472:Motor Neuron Disease / Q000175:diagnosis / Q000503:physiopathology*; D009046:Motor Neurons / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation* / Q000503:physiopathology; D009431:Neural Conduction / Q000502:physiology; D009468:Neuromuscular Diseases / Q000175:diagnosis / Q000503:physiopathology
keywords: Axonal excitability; Motor neuron disease; Multiplet discharges; Supernormality