title: Validation of bioelectrical impedance analysis in patients with amyotrophic lateral sclerosis.
abstract: BACKGROUND
  Amyotrophic lateral sclerosis (ALS) is a neurologic disease with an unfavorable prognosis that may be accompanied by malnutrition or overweight. Nutritional status is difficult to evaluate in these patients because of their physical limitations and the asymmetry of their disease involvement. Bioelectrical impedance analysis (BIA), which enables bedside analysis of body compartments, has not been adequately validated for use in patients with ALS.
  
  
  OBJECTIVE
  We compared reference measures of fat-free mass (FFM(a)), obtained by dual-energy X-ray absorptiometry, with FFM obtained by BIA and by the skinfold-thickness technique.
  
  
  METHODS
  We measured FFM(a) in 32 ALS patients. Anthropometric measures included weight, height, skinfold thickness, and arm and wrist circumferences. The fat mass obtained from the skinfold-thickness measures enabled us to calculate FFM. BIA was performed by measuring the bioimpedances at 5, 50, and 100 kHz of each side of the body and from one side to the other. FFM was calculated by using the instrument's internal software and by using 3 standard equations. The concordance between the methods was evaluated by the Bland-Altman test.
  
  
  RESULTS
  Two of the 16 measured FFM values were not significantly different from FFM(a). However, the risk of dispersion was too high to be acceptable in practice. An equation was then developed by using multivariate analysis, with impedance at 50 kHz. This equation was validated in a second population of 15 ALS patients and with the use of 2 successive measurements performed on 18 patients.
  
  
  CONCLUSIONS
  BIA is a simple technique that is valid for use in ALS patients, both for a single exam measure and for longitudinal monitoring, with the use of an adapted equation and a frequency of 50 kHz.
authors.affiliation: Nutrition Unit & Hepato-Gastroenterology Service, Dupuytren University Hospital, Limoges, France. nutrition@unilim.fr
authors.forename: Jean C
authors.initials: JC
authors.lastname: Desport
authors.forename: Pierre M
authors.initials: PM
authors.lastname: Preux
authors.forename: Corinne
authors.initials: C
authors.lastname: Bouteloup-Demange
authors.forename: Pierre
authors.initials: P
authors.lastname: Clavelou
authors.forename: Bernard
authors.initials: B
authors.lastname: Beaufrère
authors.forename: Christine
authors.initials: C
authors.lastname: Bonnet
authors.forename: Philippe P
authors.initials: PP
authors.lastname: Couratier
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D000690:Amyotrophic Lateral Sclerosis / Q000503:physiopathology*; D000886:Anthropometry; D001823:Body Composition; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009752:Nutritional Status; D015203:Reproducibility of Results; D012885:Skinfold Thickness