Guidelines on clinical presentation and management of nondystrophic myotonias.

Bas C Stunnenberg, Samantha LoRusso, W David Arnold, Richard J Barohn, Stephen C Cannon, Bertrand Fontaine, Robert C Griggs, Michael G Hanna, Emma Matthews, Giovanni Meola, Valeria A Sansone, Jaya R Trivedi, Baziel G M van Engelen, Savine Vicart, Jeffrey M Statland

Journal: Muscle & nerve 2020;62(4):430-444

PMID: 32270509

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Abstract

The nondystrophic myotonias are rare muscle hyperexcitability disorders caused by gain-of-function mutations in the SCN4A gene or loss-of-function mutations in the CLCN1 gene. Clinically, they are characterized by myotonia, defined as delayed muscle relaxation after voluntary contraction, which leads to symptoms of muscle stiffness, pain, fatigue, and weakness. Diagnosis is based on history and examination findings, the presence of electrical myotonia on electromyography, and genetic confirmation. In the absence of genetic confirmation, the diagnosis is supported by detailed electrophysiological testing, exclusion of other related disorders, and analysis of a variant of uncertain significance if present. Symptomatic treatment with a sodium channel blocker, such as mexiletine, is usually the first step in management, as well as educating patients about potential anesthetic complications.

Address: Department of Neurology, Radboud University Medical Center, Nijmegen, the Netherlands.; Department of Neurology, Ohio State University Wexner Medical Center, Columbus, Ohio.; Department of Neurology, University of Kansas Medical Center, Kansas City, Kansas.; Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California.; Assistance Publique-Hôpitaix de Paris, Sorbonne Université, INSERM, Service of Neuro-Myology and UMR 974, Institute of Myology, University Hospital Pitié-Salpêtrière, Paris, France.; Department of Neurology, University of Rochester, Rochester, New York.; MRC Centre for Neuromuscular Diseases, Department of Neuromuscular diseases, UCL Queen Square Institute of Neurology, United Kingdom.; Department of Neurorehabilitation Sciences, Casa Cura Policlinico, Milan, Italy.; Department of Biomedical Sciences for Health, University of Milan, Milan, Italy.; Neurorehabilitation Unit, University of Milan, NEuroMuscular Omnicentre (NEMO), Fondazione Serena Onlus, Milan, Italy.; Department of Neurology and Neurotherapeutics, UT Southwestern Medical Center, Dallas, Texas.

DOI: 10.1002/mus.26887

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MeSH Terms: Acetazolamide, Age of Onset, Carbonic Anhydrase Inhibitors, Chloride Channels, Electrodiagnosis, Electromyography, Fatigue, Genetic Testing, Humans, Lamotrigine, Mexiletine, Muscle Weakness, Muscle, Skeletal, Myalgia, Myotonia Congenita, Myotonic Disorders, NAV1.4 Voltage-Gated Sodium Channel, Practice Guidelines as Topic, Ranolazine, Sodium Channel Blockers, Voltage-Gated Sodium Channel Blockers