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Myotonia congenita



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

Alternative Names

Thomsen's disease; Becker's disease


Myotonia congenita is caused by a genetic change (mutation). It is passed down from either one or both parents to the 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 discharges occur in the muscles, causing a stiffness called myotonia.


The hallmark of this condition is the myotonia -- the inability of the muscle 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 in 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 appear to be muscular and well-developed. The child 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:

  • Genetic testing
  • Muscle biopsy
  • Test of the electrical activity in muscles (EMG)
Support Groups

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.

Calling your health care provider

Call your health care provider if your child has symptoms of myotonia congenita.

  • Aspiration pneumonia caused by swallowing difficulties
  • Frequent choking, gagging, or difficulty swallowing in an infant
  • Abdominal muscle weakness
  • Chronic joint problems

Treatment for symptoms includes:

  • Mexiletine
  • Phenytoin
  • Procainamide

Genetic counseling may be of interest to couples who want to have children and have a family history of myotonia congenita.


Barohn RJ. Muscle diseases. Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2008:chap 447.

Bernard G, Shevell MI. Channelopathies: a review. Pediatr Neurol. 2008 Feb;38(2):73-85.

Review Date: 3/21/2010
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., Inc.
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