title: Myotonic discharges discriminate chloride from sodium muscle channelopathies.
abstract: Non-dystrophic myotonic syndromes represent a heterogeneous group of clinically quite similar diseases sharing the feature of myotonia. These syndromes can be separated into chloride and sodium channelopathies, with gene-defects in chloride or sodium channel proteins of the sarcolemmal membrane. Myotonia has its basis in an electrical instability of the sarcolemmal membrane. In the present study we examine the discriminative power of the resulting myotonic discharges for these disorders. Needle electromyography was performed by an electromyographer blinded for genetic diagnosis in 66 non-dystrophic myotonia patients (32 chloride and 34 sodium channelopathy). Five muscles in each patient were examined. Individual trains of myotonic discharges were extracted and analyzed with respect to firing characteristics. Myotonic discharge characteristics in the rectus femoris muscle almost perfectly discriminated chloride from sodium channelopathy patients. The first interdischarge interval as a single variable was longer than 30 ms in all but one of the chloride channelopathy patients and shorter than 30 ms in all of the sodium channelopathy patients. This resulted in a detection rate of over 95%. Myotonic discharges of a single muscle can be used to better guide toward a molecular diagnosis in non-dystrophic myotonic syndromes.
authors.affiliation: Department of Neurology, Department of Neurosurgery, University of Groningen, University Medical Center Groningen, The Netherlands. Electronic address: g.drost@umcg.nl.
authors.forename: Gea
authors.initials: G
authors.lastname: Drost
authors.affiliation: Department of Neurology, Radboud University Medical Centre, The Netherlands.
authors.forename: Bas C
authors.initials: BC
authors.lastname: Stunnenberg
authors.affiliation: Department of Neurology, Diaconessenhuis Meppel, The Netherlands.
authors.forename: Jeroen
authors.initials: J
authors.lastname: Trip
authors.affiliation: Department of Epidemiology, Biostatistics and HTA, Radboud University Medical Centre, The Netherlands.
authors.forename: George
authors.initials: G
authors.lastname: Borm
authors.affiliation: Rehabilitation R&D Center, VA Palo Alto Health Care System, Palo Alto, CA, USA.
authors.forename: Kevin C
authors.initials: KC
authors.lastname: McGill
authors.affiliation: Department of Human and Clinical Genetics, Leiden University Medical Centre, The Netherlands.
authors.forename: Ieke H B
authors.initials: IH
authors.lastname: Ginjaar
authors.affiliation: Department of Neurology, Radboud University Medical Centre, The Netherlands.
authors.forename: Arendina W
authors.initials: AW
authors.lastname: van der Kooi
authors.affiliation: Department of Clinical Neurophysiology, Academic Center for Epileptology, Kempenhaeghe/Maastricht UMC+, Heeze, The Netherlands.
authors.forename: Machiel J
authors.initials: MJ
authors.lastname: Zwarts
authors.affiliation: Department of Neurology, Radboud University Medical Centre, The Netherlands.
authors.forename: Baziel G M
authors.initials: BG
authors.lastname: van Engelen
authors.affiliation: Department of Neurology, Maastricht University Medical Centre, The Netherlands.
authors.forename: Catharina G
authors.initials: CG
authors.lastname: Faber
authors.affiliation: Department of Neurology, Radboud University Medical Centre, The Netherlands; Faculty of Human Movement Sciences, MOVE Research Institute, VU University, Amsterdam, The Netherlands.
authors.forename: Dick F
authors.initials: DF
authors.lastname: Stegeman
authors.affiliation: Rehabilitation R&D Center, VA Palo Alto Health Care System, Palo Alto, CA, USA.
authors.forename: Zoia
authors.initials: Z
authors.lastname: Lateva
mesh_terms: D000328:Adult; D000368:Aged; D053447:Channelopathies / Q000175:diagnosis* / Q000235:genetics / Q000503:physiopathology*; D018118:Chloride Channels / Q000235:genetics*; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology; D020967:Myotonic Disorders / Q000175:diagnosis* / Q000235:genetics / Q000503:physiopathology*; D062553:NAV1.4 Voltage-Gated Sodium Channel / Q000235:genetics*; D055815:Young Adult
chemical_list: C086321:CLC-1 channel; D018118:Chloride Channels; D062553:NAV1.4 Voltage-Gated Sodium Channel; C106251:SCN4A protein, human
keywords: Chloride channelopathies; Diagnosis; Myotonic discharges; Needle electromyography; Non-dystrophic myotonic syndromes; Sodium channelopathies