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Myotonia congenita

Definition

Myotonia congenita is an inherited condition that affects muscle relaxation. It is congenital, meaning that it is present from birth.

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Alternative Names

Thomsen's disease; Becker's disease

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
Muscle biopsy

Treatment

Mexiletine is a medication that treats symptoms of myotonia congenita. Other treatments include:

Phenytoin
Procainamide
Quinine
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.

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.

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