Myotonia is the main feature of both myotonic dystrophy (DM) and non-dystrophic myotonia (NDM). It is felt as stiffness, pain, fatigue, and weakness. In France, mexiletine, a non-selective voltage-gated sodium channel blocker, is approved for the treatment of myotonia in adults with NDM, and it has a temporary recommendation for use in the symptomatic treatment of DM in adults. However, it is not currently licensed for treating myotonia in children due to the lack of studies on its use in pediatrics. This has meant heterogeneous practices in its utilization and has led to prescriber reluctance, which has jeopardized accessibility. We undertook a professional practice survey of French pediatric neuromuscular centers to determine their prescribing habits for mexiletine, assessing indications, doses, efficacy, and tolerance.

One medical pediatric professional from each French pediatric neuromuscular center belonging to the national neuromuscular network (FILNEMUS) was invited to complete an anonymous questionnaire.

In total, 34 healthcare professionals responded. Of these, 16 had already treated a child for myotonia with mexiletine. Mexiletine was prescribed in one third of pediatric patients with NDM, but it was used in only 3% of DM type 1 patients and in no DM type 2 patients. Pre-treatment assessment always included a cardiac evaluation; however, the method of introduction (inpatient vs. outpatient basis), dosage adjustment, and efficacy evaluation ranged widely. More than half of the respondents reported a high efficacy of mexiletine in their patients; only three reported moderate adverse events (dyspepsia, loss of appetite, and asthenia).

The findings of this first survey on mexiletine for pediatric myotonia in France lend support for the creation of future national guidelines.