Stunnenberg BC, et al. - In a series of N-of-1 trials of mexiletine (600 mg daily) vs placebo in 27 patients with nondystrophic myotonia, researchers studied the efficacy of mexiletine in nondystrophic myotonia and compared the results of this innovative design with a previous RCT. Between February 2014 and June 2015, 30 Dutch adult patients with genetically confirmed nondystrophic myotonia (38 patients screened) were recruited. In a previous randomized clinical trial, there was a reduction in mean daily-reported muscle stiffness that was consistent with the treatment effect. The effectiveness of mexiletine for treatment of nondystrophic myotonia as well as the feasibility of N-of-1 trials for evaluating interventions in some chronic rare diseases was supported in this investigation. Gastrointestinal discomfort was the most common adverse event.