title: Electromyography guides toward subgroups of mutations in muscle channelopathies.
abstract: Myotonic syndromes and periodic paralyses are rare disorders of skeletal muscle characterized mainly by muscle stiffness or episodic attacks of weakness. Familial forms are caused by mutations in genes coding for skeletal muscle voltage-gated ion channels. Exercise is known to trigger, aggravate, or relieve the symptoms. Therefore, exercise can be used as a functional test in electromyography to improve the diagnosis of these muscle disorders. Abnormal changes in the compound muscle action potential can be disclosed using different exercise tests. We report the outcome of an inclusive electromyographic survey of a large population of patients with identified ion channel gene defects. Standardized protocols comprising short and long exercise tests were applied on 41 unaffected control subjects and on 51 case patients with chloride, sodium, or calcium channel mutations known to cause myotonia or periodic paralysis. These tests disclosed significant changes of compound muscle action potential, which generally matched the clinical symptoms. Combining the responses to the different tests defined five electromyographic patterns (I-V) that correlated with subgroups of mutations and may be used in clinical practice as guides for molecular diagnosis. We hypothesize that mutations are segregated into the different electromyographic patterns according to the underlying pathophysiological mechanisms.
authors.affiliation: Department of Physiology, Groupe Hospitalier Pitié-Salpêtrière and Université Pierre et Marie Curie, Paris, France. emfou@ccr.jussieu.fr
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Fournier
authors.forename: Marianne
authors.initials: M
authors.lastname: Arzel
authors.forename: Damien
authors.initials: D
authors.lastname: Sternberg
authors.forename: Savine
authors.initials: S
authors.lastname: Vicart
authors.forename: Pascal
authors.initials: P
authors.lastname: Laforet
authors.forename: Bruno
authors.initials: B
authors.lastname: Eymard
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Willer
authors.forename: Nacira
authors.initials: N
authors.lastname: Tabti
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; D002648:Child; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods*; D015444:Exercise / Q000502:physiology; D005080:Exercise Test / Q000379:methods; D005260:Female; D006801:Humans; D007473:Ion Channels / Q000145:classification / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D009135:Muscular Diseases / Q000145:classification / Q000235:genetics* / Q000534:rehabilitation; D009154:Mutation; D015221:Potassium Channels / Q000235:genetics / Q000502:physiology; D015222:Sodium Channels / Q000235:genetics / Q000502:physiology; D016896:Treatment Outcome
chemical_list: D015220:Calcium Channels; D007473:Ion Channels; D015221:Potassium Channels; D015222:Sodium Channels