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A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M.; 2013.
A.D.A.M. Medical Encyclopedia.
Myotonia congenita is an inherited condition that affects muscle relaxation. It is congenital, meaning that it is present from birth.
Causes, incidence, and risk factors
Myotonia congenita is caused by a genetic change (mutation). It is passed down from either one or both parents to their children (inherited).
Myotonia congenita is caused by a problem in the part of the muscle cells that are needed for muscles to relax. Abnormal repeated electrical signals occur in the muscles, causing a stiffness called myotonia.
Symptoms
The hallmark of this condition is myotonia -- the muscles are unable to quickly relax after contracting. For example, after a handshake, the person is only very slowly able to open and pull away his hand.
Early symptoms may include:
- Difficulty swallowing
- Gagging
- Stiff movements that improve when they are repeated
- Shortness of breath or tightening of the chest at the beginning of exercise
Children with myotonia congenita often look muscular and well-developed. They may not have symptoms of myotonia congenita until age 2 or 3.
Signs and tests
The doctor may ask if there is a family history of myotonia congenita.
Tests include:
- Electromyography (EMG, a test of the electrical activity of the muscles)
- Genetic testing
Treatment
Mexiletine is a medication that treats symptoms of myotonia congenita. Other treatments include:
- Tocainide
Expectations (prognosis)
People with this condition can do well. Symptoms only occur when a movement is first started. After a few repetitions, the muscle relaxes and the movement becomes normal. Symptoms may improve later in life.
Complications
- Aspiration pneumonia caused by swallowing difficulties
- Frequent choking, gagging, or trouble swallowing in an infant
- Long-term (chronic) joint problems
- Weakness of the abdominal muscles
Calling your health care provider
Call your health care provider if your child has symptoms of myotonia congenita.
Prevention
Couples who want to have children and who have a family history of myotonia congenita should consider genetic counseling.
References
- Bernard G, Shevell MI. Channelopathies: a review. Pediatr Neurol. 2008;38:73-85. [PubMed: 18206787]
- Chinnery PF. Muscle diseases. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 429.
- Kerchner GA, Lenz RA, Ptacek LJ. Channelopathies: Episodic and electrical disorders of the nervous system. In: Bradley WG, Daroff RB, Fenichel GM, Jankovic J, eds. Neurology in Clinical Practice. 5th ed. Philadelphia, Pa: Butterworth-Heinemann: 2008:chap 68.
Review Date: 2/5/2012.
Reviewed by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; Luc Jasmin, MD, PhD, Department of Neurosurgery at Cedars-Sinai Medical Center, Los Angeles, and Department of Anatomy at UCSF, San Francisco, CA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.
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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.
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