title: Localized muscle impedance abnormalities in amyotrophic lateral sclerosis.
abstract: OBJECTIVE
  To assess changes in electrical impedance myography (EIM) parameters in amyotrophic lateral sclerosis (ALS).
  
  
  METHODS
  Ten patients with ALS and a cohort of normal subjects underwent EIM testing of tibialis anterior. Montages using voltage and current electrodes placed at a distance (far) and in close proximity (near) were compared. The EIM parameters, resistance (R), reactance (X), and phase (theta) in the patients with ALS, were compared with normal values.
  
  
  RESULTS
  theta measured at 50 kHz using the near montage was most sensitive to the presence of ALS, with 9 of 10 patients with ALS having smaller theta values than the calculated lower limit of normal. theta using the far montage and X using both the near and far montages were also sensitive to disease, whereas R did not seem to be useful.
  
  
  CONCLUSIONS
  EIM is sensitive to muscle abnormalities in ALS, with theta measured with near montages providing the best results.
authors.affiliation: From the Division of Neuromuscular Diseases, Department of Neurology, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA, USA.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Tarulli
authors.forename: Lindsay P
authors.initials: LP
authors.lastname: Garmirian
authors.forename: Patricia M
authors.initials: PM
authors.lastname: Fogerson
authors.forename: Seward B
authors.initials: SB
authors.lastname: Rutkove
mesh_terms: D000328:Adult; D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000175:diagnosis* / Q000503:physiopathology*; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009213:Myography / Q000379:methods; D012680:Sensitivity and Specificity