title: Cold extends electromyography distinction between ion channel mutations causing myotonia.
abstract: OBJECTIVE
  Myotonias are inherited disorders of the skeletal muscle excitability. Nondystrophic forms are caused by mutations in genes coding for the muscle chloride or sodium channel. Myotonia is either relieved or worsened by repeated exercise and can merge into flaccid weakness during exposure to cold, according to causal mutations. We designed an easy electromyography (EMG) protocol combining repeated short exercise and cold as provocative tests to discriminate groups of mutations.
  
  
  METHODS
  Surface-recorded compound muscle action potential was used to monitor muscle electrical activity. The protocol was applied on 31 unaffected control subjects and on a large population of 54 patients with chloride or sodium channel mutations known to cause the different forms of myotonia.
  
  
  RESULTS
  In patients, repeated short exercise test at room temperature disclosed three distinct abnormal patterns of compound muscle action potential changes (I-III), which matched the clinical symptoms. Combining repeated exercise with cold exposure clarified the EMG patterns in a way that enabled a clear correlation between the electrophysiological and genetic defects.
  
  
  CONCLUSIONS
  We hypothesize that segregation of mutations into the different EMG patterns depended on the underlying pathophysiological mechanisms. Results allow us to suggest EMG guidelines for the molecular diagnosis, which can be used in clinical practice.
authors.affiliation: Fédération de Neurophysiologie Clinique, Groupe Hospitalier Pitié-Salpêtrière, Assistance Publique-Hôpitaux de Paris, Université Pierre et Marie Curie, Paris. emmanuel.fournier@upmc.fr
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Fournier
authors.forename: Karine
authors.initials: K
authors.lastname: Viala
authors.forename: Hélène
authors.initials: H
authors.lastname: Gervais
authors.forename: Damien
authors.initials: D
authors.lastname: Sternberg
authors.forename: Marianne
authors.initials: M
authors.lastname: Arzel-Hézode
authors.forename: Pascal
authors.initials: P
authors.lastname: Laforêt
authors.forename: Bruno
authors.initials: B
authors.lastname: Eymard
authors.forename: Nacira
authors.initials: N
authors.lastname: Tabti
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Willer
authors.forename: Christophe
authors.initials: C
authors.lastname: Vial
authors.forename: Bertrand
authors.initials: B
authors.lastname: Fontaine
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000293:Adolescent; D000328:Adult; D000368:Aged; D015220:Calcium Channels / Q000235:genetics / Q000502:physiology; D003080:Cold Temperature; D004576:Electromyography / Q000379:methods*; D005080:Exercise Test / Q000379:methods; D005260:Female; D006801:Humans; D007473:Ion Channels / Q000145:classification / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology; D009154:Mutation; D009222:Myotonia / Q000175:diagnosis / Q000235:genetics* / Q000503:physiopathology; D015221:Potassium Channels / Q000235:genetics / Q000502:physiology; D015222:Sodium Channels / Q000235:genetics / Q000502:physiology; D013697:Thermosensing / Q000502:physiology; D013997:Time Factors
chemical_list: D015220:Calcium Channels; D007473:Ion Channels; D015221:Potassium Channels; D015222:Sodium Channels