The Dystrophic and Nondystrophic Myotonias

Valeria A. Sansone, MD Muscle and Neuromuscular Junction Disorders p. 1889-1915 December 2016, Vol.22, No.6 doi: 10.1212/CON.0000000000000414
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Purpose of Review: This article describes clinical and electrical myotonia and provides an update on the classification, diagnosis, and management of myotonic disorders.

Recent Findings: In the myotonic dystrophies, antisense oligonucleotides provide a general strategy to correct RNA gain of function and modulate the expression of CTG expanded repeats; they are currently being tested in a phase 1-2 randomized controlled trial in patients with adult-onset myotonic dystrophy type 1. New genetic mutations are continuously being identified in the nondystrophic myotonias involving sodium and chloride channels. This contributes to the difficulty in describing genotype-phenotype correlations as the same mutations can give rise to different phenotypes, and the same phenotypes can arise from different mutations. Pharmacologic therapy is moving toward mutation-targeted treatments.

Summary: This article describes the clinical and diagnostic characteristics and management of the myotonic dystrophies and the nondystrophic myotonias. Clinical features of the congenital, juvenile, and classic adult forms of myotonic dystrophy type 1 are reviewed, and for the adult form, reference is made to the main diagnostic and follow-up tests for which general consensus exists. The different clinical presentations of myotonic dystrophy type 2 and its main differential diagnostic options are also discussed. The clinical spectrum of the sodium and chloride channelopathies is described, and clinical diagnostic clues to differentiate between these two groups are provided. Therapeutic options for patients with nondystrophic myotonias are also presented with reference to literature review and the author’s personal experience.

Address correspondence to Dr Valeria A. Sansone, The NEMO Clinical Center, Neurorehabilitation Unit, University of Milan, Niguarda Hospital, Piazza Opedale Maggiore 3, Milan, Italy 20162, [email protected].

Relationship Disclosure: Dr Sansone has received research support from Telethon (Unione Italiana Lotta alla Distrofia Musculare [UILDM] grant GUP15004).

Unlabeled Use of Products/Investigational Use Disclosure: Dr Sansone discusses the unlabeled/investigational use of clomipramine, flecainide, imipramine, mexiletine, and tocainide for the treatment of myotonia; acetazolamide and dichlorphenamide for the treatment of periodic paralysis; creatinine and tricyclic antidepressants for the treatment of muscle pain; and modafinil for the treatment of fatigue in myotonic dystrophy.

Supplemental digital content: Videos accompanying this article are cited in the text as Supplemental Digital Content. Videos may be accessed by clicking on links provided in the HTML, PDF, and app versions of this article; the URLs are provided in the print version. Video legends begin on page 1911.

Copyright © 2016 by the American Academy of Neurology.