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Original Investigation
December 11, 2018

Effect of Mexiletine on Muscle Stiffness in Patients With Nondystrophic Myotonia Evaluated Using Aggregated N-of-1 Trials

Author Affiliations
  • 1Department of Neurology, Donders Institute for Brain Cognition and Behaviour, Radboud University Medical Center, Nijmegen, the Netherlands
  • 2Department of Neurology, Amsterdam University Medical Center, University of Amsterdam, Amsterdam Neuroscience, Amsterdam, the Netherlands
  • 3Department of Health Evidence, Radboud University Medical Center, Nijmegen, the Netherlands
  • 4Department of Neurology, University of Kansas Medical Center, Kansas City
  • 5Department of Neurology, University of Rochester Medical Center, Rochester, New York
  • 6Department of Cardiology, Radboud University Medical Center, Nijmegen, the Netherlands
  • 7Department of Neurology and Neurotherapeutics, UT Southwestern Medical Center, Dallas, Texas
  • 8MRC Centre for Neuromuscular Diseases, UCL Institute of Neurology and National Hospital for Neurology and Neurosurgery, London, United Kingdom
  • 9Department of Pharmacology–Toxicology, Radboud University Medical Center, Nijmegen, the Netherlands
  • 10University of Groningen, Department of Neurology and Neurosurgery, University Medical Center Groningen, Groningen, the Netherlands
JAMA. 2018;320(22):2344-2353. doi:10.1001/jama.2018.18020
Key Points

Question  Does a study of mexiletine in patients with nondystrophic myotonia using an aggregated N-of-1 trials design produce efficacy results consistent with those from a randomized clinical trial?

Findings  In a series of N-of-1 trials of mexiletine vs placebo in 27 patients with nondystrophic myotonia, there was a reduction in mean daily-reported muscle stiffness of 3.12 of a possible 9 points. This compares with a reduction of 2.69 points in a published randomized clinical trial.

Meaning  These findings support the efficacy of mexiletine and also support the potential value of N-of-1 trials for assessing interventions in some chronic rare diseases.

Abstract

Importance  In rare diseases it is difficult to achieve high-quality evidence of treatment efficacy because of small cohorts and clinical heterogeneity. With emerging treatments for rare diseases, innovative trial designs are needed.

Objective  To investigate the effectiveness of mexiletine in nondystrophic myotonia using an aggregated N-of-1 trials design and compare results between this innovative design and a previously conducted RCT.

Design, Setting, and Participants  A series of aggregated, double-blind, randomized, placebo-controlled N-of-1-trials, performed in a single academic referral center. Thirty Dutch adult patients with genetically confirmed nondystrophic myotonia (38 patients screened) were enrolled between February 2014 and June 2015. Follow-up was completed in September 2016.

Interventions  Mexiletine (600 mg daily) vs placebo during multiple treatment periods of 4 weeks.

Main Outcomes and Measures  Reduction in daily-reported muscle stiffness on a scale of 1 to 9, with higher scores indicating more impairment. A Bayesian hierarchical model aggregated individual N-of-1 trial data to determine the posterior probability of reaching a clinically meaningful effect of a greater than 0.75-point difference.

Results  Among 30 enrolled patients (mean age, 43.4 [SD, 15.24] years; 22% men; 19 CLCN1 and 11 SCN4A genotype), 27 completed the study and 3 dropped out (1 because of a serious adverse event). In 24 of the 27 completers, a clinically meaningful treatment effect was found. In the Bayesian hierarchical model, mexiletine resulted in a 100% posterior probability of reaching a clinically meaningful reduction in self-reported muscle stiffness for the nondystrophic myotonia group overall and the CLCN1 genotype subgroup and 93% posterior probability for the SCN4A genotype subgroup. In the total nondystrophic myotonia group, the median muscle stiffness score was 6.08 (interquartile range, 4.71-6.80) at baseline and was 2.50 (95% credible interval [CrI], 1.77-3.24) during the mexiletine period and 5.56 (95% CrI, 4.73-6.39) during the placebo period; difference in symptom score reduction, 3.06 (95% CrI, 1.96-4.15; n = 27) favoring mexiletine. The most common adverse event was gastrointestinal discomfort (21 mexiletine [70%], 1 placebo [3%]). One serious adverse event occurred (1 mexiletine [3%]; allergic skin reaction). Using frequentist reanalysis, mexiletine compared with placebo resulted in a mean reduction in daily-reported muscle stiffness of 3.12 (95% CI, 2.46-3.78), consistent with the previous RCT treatment effect of 2.69 (95% CI, 2.12-3.26).

Conclusions and Relevance  In a series of N-of-1 trials of mexiletine vs placebo in patients with nondystrophic myotonia, there was a reduction in mean daily-reported muscle stiffness that was consistent with the treatment effect in a previous randomized clinical trial. These findings support the efficacy of mexiletine for treatment of nondystrophic myotonia as well as the feasibility of N-of-1 trials for assessing interventions in some chronic rare diseases.

Trial Registration  ClinicalTrials.gov Identifier: NCT02045667

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