The MYOMEX study was a multicentre, randomised, double-blind, placebo-controlled, cross-over study aimed to compare the effects of mexiletine vs. placebo in patients with myotonia congenita (MC) and paramyotonia congenita (PC). The primary endpoint was the self-reported score of stiffness severity on a 100 mm visual analogic scale (VAS). Mexiletine treatment started at 200 mg/day and was up-titrated by 200 mg increment each three days to reach a maximum dose of 600 mg/day for total treatment duration of 18 days for each cross-over period. The modified intent-to-treat population included 25 patients (13 with MC and 12 with PC; mean age, 43.0 years; male, 68.0%). The median VAS score for mexiletine was 71.0 at baseline and decreased to 16.0 at the end of the treatment while the score did not change for placebo (81.0 at baseline vs. 78.0 at end of treatment). A mixed effects linear model analysis on ranked absolute changes showed a significant effect of treatment (p < 0.001). The overall score of the Individualized Neuromuscular Quality of Life questionnaire (INQoL) was significantly improved (p < 0.001). No clinically significant adverse events were reported. In conclusion, mexiletine improved stiffness and quality of life in patients with nondystrophic myotonia and was well tolerated.

MYOMEX 研究是一项多中心、随机、双盲、安慰剂对照、交叉研究，旨在比较美西律与安慰剂对先天性肌强直 (MC) 和先天性副肌强直 (PC) 患者的影响。主要终点是在 100 mm 视觉模拟量表 (VAS) 上自我报告的僵硬严重程度评分。美西律治疗以 200 毫克/天开始，每三天以 200 毫克的增量递增至最大剂量 600 毫克/天，每个交叉期的总治疗持续时间为 18 天。改良的意向治疗人群包括 25 名患者（13 名 MC 和 12 名 PC；平均年龄，43.0 岁；男性，68.0%）。基线时美西律的中位 VAS 评分为 71.0，在治疗结束时降至 16.0，而安慰剂的评分没有变化（基线时为 81.0 对 78.0）。0 治疗结束）。对排名绝对变化的混合效应线性模型分析显示治疗效果显着（p  < 0.001)。个体化神经肌肉生活质量问卷 (INQoL) 的总分显着提高 ( p  < 0.001)。未报告有临床意义的不良事件。总之，美西律改善了非营养不良性肌强直患者的僵硬和生活质量，并且耐受性良好。