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Schneider-Gold, Christiane; Schoser, Benedikt; Ellrichmann, Gisa; Quasthoff, Stefan; Lehmann-Horn, Frank; Sinnreich, Michael (2018): Myotone Dystrophien, nicht dystrophe Myotonien und periodische Paralysen. In: Aktuelle Neurologie, Vol. 45, No. 3: pp. 167-177
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In the last years several new therapeutic options and strategies in the treatment of myotonias, myotonic dystrophies and periodic paralyses have been published. All relevant novel aspects in the treatment of muscle ion channel diseases are summarized in the respective guideline of the German Society of Neurology which has been updated very recently. The most important points are: Mexiletine is no more available in Germany, but it is still possible to get retarded 100mg or 200 preparations from Japan, the U.S.or Canada. The positive effects of mexiletine in the treatment of myotonic symptoms even in myotonic dystrophy type I have convincingly been shown in a double-blind placebo controlled study (Logigian et al., 2010). In a very recent study dichlorphenamide, a carboanhydrase inhibitor, was shown to be effective in hypo- and hyperkalemic periodic paralyses leading to significant reduction of the frequency of attacks (Sansone et al., 2016). In this study two randomized placebo-controlled studies over a time period of 9 weeks followed by a one year extension phase with application of dichlorphenamide in all patients were combined. The comparative actazolamide arm of the study had to be closed because most patients preferred dichlorphenamide for less subjective side effects. The main side effects reported under dichlorphenamide were paraesthesias, reduced velocity of thinking, and development of renal stones. The study did not allow for retrieving conclusions regarding the relation of efficacy and genotype. The most frequent mutations were T704M (Nav1.4) in hyperkalemic periodic paralysis and R528H (Cav1.1) and R1239H (Cav1.1) in hypokalemic paralysis. One patient with hypokalemic periodic paralysis and a pR222W (Nav1.4) mutation showed deterioration of his symptoms while taking dichlorphenamide. Dichlorphenamide is now available in the US, in Europe it has not been finally approved so far;but the classification as "orphan drug allows for prescription. Another recent double-blind placebo controlled study showed significant improvement of myotonic symptoms as compared to baseline in 22 patients with nondystrophic myotonia treated with either lamotrigine 300mg daily (Anderson G et al., 2017). In a recently published open observational study ranolazine, 2x500mg was shown to significantly reduce clinical and EMG myotonia and to improve muscle weakness in 13 patients with chloride channel (Arnold WD et al., 2017).