Myotonia congenita

Causes

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.

Exams 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

Outlook (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.

Possible 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

When to Contact a Medical Professional

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.

Alternative Names

Thomsen's disease; Becker's disease

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.

Update Date: 2/5/2012

Updated 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.