Drug treatment for myotonia (delayed muscle relaxation after contraction) in muscle diseases such as myotonic dystrophy and myotonia congenita

Myotonia is an abnormal delay in the relaxation of muscles after contraction. It is a key symptom in a number of muscle diseases called myotonic disorders. It can be mild or severe, interfering with daily activities such as walking, climbing stairs or opening and closing the eyelids. It can be worse after periods of rest or triggered by cold or fatigue. People with mild myotonia can manage their disease without medication but in severe cases treatment is usually necessary. Drugs that have been used to treat myotonia include sodium channel blockers such as procainamide, phenytoin and mexiletine, tricyclic antidepressant drugs such as clomipramine or imipramine, benzodiazepines, calcium antagonists, taurine and prednisone. This review describes ten randomised controlled trials which tested the effectiveness of twelve different drug treatments. The review was updated in July 2009 and no new trials were found. The ten trials included a total of 143 participants of which 113 had myotonic dystrophy and 30 had myotonia congenita. The trials were generally small and of poor quality. Meta-analysis was not possible due to a lack of appropriate trials and data. Two small studies suggested that clomipramine and imipramine might have a short-term beneficial effect on the myotonia in myotonic dystrophy and one small study suggested that taurine might have a long-term beneficial effect in myotonic dystrophy. Minor side effects such as dry mouth and dizziness were reported with clomipramine and imipramine, but not with taurine. It was not possible to determine whether drug treatment is safe and effective for myotonia in people with a myotonic disorder based on the evidence from the ten trials included in this review. Larger, well-designed randomised controlled trials are needed.

Authors' conclusions: 

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. Larger, well-designed randomised controlled trials are needed to assess the efficacy and tolerability of drug treatment for myotonia.

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Background: 

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.

Objectives: 

To consider the evidence from randomised controlled trials on the efficacy and tolerability of drug treatment in myotonia .

Search strategy: 

In July 2009 we updated the searches of the Cochrane Neuromuscular Disease Group Trials Specialized Register , The Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 3, 2009), MEDLINE (from January 1966) and EMBASE (from January 1980). We hand searched the grey literature and contacted disease experts and anti-myotonic drug manufacturers.

Selection criteria: 

We considered all (including quasi) randomised trials of participants with myotonia treated with any drug treatment versus no therapy, placebo or any other active drug treatment.

Primary outcome: reduction of clinical myotonia.

Secondary outcomes:
(1) clinical relaxation time; (2) electromyographic relaxation time; (3) stair test; (4) presence of percussion myotonia; and (5) adverse events.

Data collection and analysis: 

Two review authors extracted the data independently onto standardised extraction forms. Meta-analysis was not possible.

Main results: 

No new trials were found for this update.Ten double-blind or single-blind crossover studies involved a total of 143 participants of whom 113 had myotonic dystrophy type 1 and 30 had myotonia congenita. The studies were of poor quality and did not provide adequate data.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.

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