title: A quantitative measure of handgrip myotonia in non-dystrophic myotonia.
abstract: BACKGROUND
  Non-dystrophic myotonia (NDM) is characterized by myotonia without muscle wasting. A standardized quantitative myotonia assessment (QMA) is important for clinical trials.
  
  
  METHODS
  Myotonia was assessed in 91 individuals enrolled in a natural history study using a commercially available computerized handgrip myometer and automated software. Average peak force and 90% to 5% relaxation times were compared with historical normal controls studied with identical methods.
  
  
  RESULTS
  Thirty subjects had chloride channel mutations, 31 had sodium channel mutations, 6 had DM2 mutations, and 24 had no identified mutation. Chloride channel mutations were associated with prolonged first handgrip relaxation times and warm-up on subsequent handgrips. Sodium channel mutations were associated with prolonged first handgrip relaxation times and paradoxical myotonia or warm-up, depending on underlying mutations. DM2 subjects had normal relaxation times but decreased peak force. Sample size estimates are provided for clinical trial planning.
  
  
  CONCLUSIONS
  QMA is an automated, non-invasive technique for evaluating myotonia in NDM.
authors.affiliation: Department of Neurology, University of Rochester Medical Center, Rochester, New York, USA.
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Statland
authors.forename: Brian N
authors.initials: BN
authors.lastname: Bundy
authors.forename: Yunxia
authors.initials: Y
authors.lastname: Wang
authors.forename: Jaya R
authors.initials: JR
authors.lastname: Trivedi
authors.forename: Dipa
authors.initials: D
authors.lastname: Raja Rayan
authors.forename: Laura
authors.initials: L
authors.lastname: Herbelin
authors.forename: Merideth
authors.initials: M
authors.lastname: Donlan
authors.forename: Rhonda
authors.initials: R
authors.lastname: McLin
authors.forename: Katy J
authors.initials: KJ
authors.lastname: Eichinger
authors.forename: Karen
authors.initials: K
authors.lastname: Findlater
authors.forename: Liz
authors.initials: L
authors.lastname: Dewar
authors.forename: Shree
authors.initials: S
authors.lastname: Pandya
authors.forename: William B
authors.initials: WB
authors.lastname: Martens
authors.forename: Shannon L
authors.initials: SL
authors.lastname: Venance
authors.forename: Emma
authors.initials: E
authors.lastname: Matthews
authors.forename: Anthony A
authors.initials: AA
authors.lastname: Amato
authors.forename: Michael G
authors.initials: MG
authors.lastname: Hanna
authors.forename: Robert C
authors.initials: RC
authors.lastname: Griggs
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Barohn
mesh_terms: D000328:Adult; D000368:Aged; D018118:Chloride Channels / Q000235:genetics; D003936:Diagnosis, Computer-Assisted / Q000379:methods / Q000592:standards; D005080:Exercise Test / Q000379:methods* / Q000592:standards; D005260:Female; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D018908:Muscle Weakness / Q000175:diagnosis* / Q000235:genetics / Q000503:physiopathology*; D009154:Mutation; D009222:Myotonia / Q000175:diagnosis* / Q000235:genetics / Q000503:physiopathology*; D015222:Sodium Channels / Q000235:genetics; D055815:Young Adult
chemical_list: D018118:Chloride Channels; D015222:Sodium Channels