Drug treatment for myotonia

Abnormal delayed relaxation of skeletal muscles, known as myotonia, can cause disability in myotonic disorders. Sodium channel blockers, tricyclic antidepressive drugs, benzodiazepines, calcium-antagonists, taurine and prednisone may be of use in reducing myotonia.

To consider the evidence from randomised controlled trials on the efficacy and tolerability of drug treatment in patients with clinical myotonia due to a myotonic disorder.

We searched the Cochrane Neuromuscular Disease Group trials register (April 2004), MEDLINE (January 1966 to December 2003) and EMBASE (January 1980 to December 2003). Grey literature was handsearched and reference lists of identified studies and reviews were examined. Authors, disease experts and manufacturers of anti-myotonic drugs were contacted.

We considered all (quasi) randomised trials of participants with myotonia treated with any drug treatment versus no therapy, placebo or any other active drug treatment. The primary outcome measure was:reduced clinical myotonia using two categories: (1) no residual myotonia or improvement of myotonia or (2) No change or worsening of myotonia. Secondary outcome measures were:(1) clinical relaxation time; (2) electromyographic relaxation time; (3) stair test; (4) presence of percussion myotonia; and (5) proportion of adverse events.

Two authors extracted the data independently onto standardised extraction forms and disagreements were resolved by discussion.

Nine randomised controlled trials were found comparing active drug treatment versus placebo or another active drug treatment in patients with myotonia due to a myotonic disorder. Included trials were double-blind or single-blind crossover studies involving a total of 137 patients of which 109 had myotonic dystrophy type 1 and 28 had myotonia congenita. The studies were of poor quality. Therefore, we were not able to analyse the results of all identified studies. Two small crossover studies without a washout period demonstrated a significant effect of imipramine and taurine in myotonic dystrophy. One small crossover study with a washout period demonstrated a significant effect of clomipramine in myotonic dystrophy. Meta-analysis was not possible.

Due to insufficient good quality data and lack of randomised studies, it is impossible to determine whether drug treatment is safe and effective in the treatment of myotonia. Small single studies give an indication that clomipramine and imipramine have a short-term beneficial effect and that taurine has a long-term beneficial effect on myotonia. Larger, well-designed randomised controlled trials are needed to assess the efficacy and tolerability of drug treatment for myotonia.