Spectrum of Nondystrophic Skeletal Muscle Channelopathies in Children.
The nondystrophic skeletal muscle channelopathies are a group of disorders caused by mutations of various voltage-gated ion channel genes, including nondystrophic myotonia and periodic paralysis.



We identified patients with a diagnosis of muscle channelopathy from our neuromuscular database in a tertiary care pediatric center from 2005 to 2015. We then performed a retrospective review of their medical records for demographic characteristics, clinical features, investigations, treatment, and follow-up.



Thirty-three patients were identified. Seventeen had nondystrophic myotonia. Seven of them had chloride channelopathy (four Becker disease and three Thomsen disease). Warm-up phenomenon and muscle hypertrophy were common clinical manifestations in this subgroup. Ten patients had sodium channelopathy (four paramyotonia congenita and six other sodium channel myotonia). Stiffness of the facial muscles was an important presenting symptom, and eyelid myotonia was a common clinical finding in this subgroup. The majority of these patients had electrical myotonia. Mexiletine was effective in controlling the symptoms in patients who had received treatment. Sixteen children had periodic paralysis (four hyperkalemic periodic paralysis, eight hypokalemic periodic paralysis, and four Andersen-Tawil syndrome). Acetazolamide was commonly used to prevent paralytic attacks and was found to be effective.



Nondystrophic muscle channelopathies present with diverse clinical manifestations (myotonia, muscle hypertrophy, proximal weakness, swallowing difficulties, and periodic paralysis). Cardiac arrhythmias are potentially life threatening in Andersen-Tawil syndrome. Timely identification of these disorders is helpful for effective symptomatic management and genetic counseling.
Department of Neurology, Boston Children's Hospital, Boston, MA.
Fouad
F
Al-Ghamdi
Department of Neurology, Boston Children's Hospital, Boston, MA.
Basil T
BT
Darras
Department of Neurology, Boston Children's Hospital, Boston, MA. Electronic address: partha.ghosh@childrens.harvard.edu.
Partha S
PS
Ghosh
D050030:Andersen Syndrome / Q000209:etiology / Q000235:genetics; D053447:Channelopathies / Q000150:complications* / Q000235:genetics / Q000473:pathology*; D002648:Child; D002675:Child, Preschool; D004576:Electromyography; D005260:Female; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009154:Mutation / Q000235:genetics; D062553:NAV1.4 Voltage-Gated Sodium Channel / Q000235:genetics; D009468:Neuromuscular Diseases / Q000209:etiology* / Q000235:genetics; D020513:Paralysis, Hyperkalemic Periodic / Q000209:etiology / Q000235:genetics; D012189:Retrospective Studies
D062553:NAV1.4 Voltage-Gated Sodium Channel; C106251:SCN4A protein, human
children; muscle disorders; nondystrophic myotonia; periodic paralysis; skeletal muscle channelopathies