Steinert disease: Mexiletine is not effective for walking but for myotonia

Steinert disease (DM1) is one of the most common neuromuscular diseases in adults. It affects both muscles and others organs such as heart, eye, endocrine system, digestive tract or nervous system… Cardiac complications are one of the most serious manifestations, with a significant risk of sudden death in the absence of prophylactic treatment. Myotonia, especially to hands, is observed in the majority of patients and can be particularly disabling.

In an article published in October 2020, an American team reports the eagerly awaited results of a clinical trial aimed at evaluating the efficacy, in DM1, of mexiletine, a molecule given orally already having a marketing authorization in non-dystrophic myotonias. The trial was double-blind in two groups of 20 adults with DM1, with the six-minute walk test as the primary endpoint. The evolution judged at six months did not record any benefit in terms of walking, unlike manual myotonia which was objectively, but not subjectively, improved during the period of exposure to the product. The authors finally underline the good tolerance of the drug, in particular at the cardiac level.

In another article published in October 2021, an English team confirms, based on the retrospective analysis of data from 25 patients with myotonic dystrophy, the good efficacy of mexiletine on myotonia (judged to be at least partially effective by 96% of patients) and its good cardiac tolerance.


Mexiletine in myotonic dystrophy type-1: A randomized, double-blind, placebo-controlled trial. C Heatwole, E Luebbe, S Rosero et al. Neurology. 2020 (Oct).

Long-term Safety and Efficacy of Mexiletine in Myotonic Dystrophy Types 1 and 2. Christina Mousele , Emma Matthews , Robert D S et al. Neurol Clin Pract . 2021 Oct