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Myotonia congenita

Thomsen's disease; Becker's disease

Myotonia congenita is an inherited condition that affects muscle relaxation. It is congenital, meaning that it is present from birth. It occurs more frequently in northern Scandinavia.

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Superficial anterior muscles
Deep anterior muscles
Tendons and muscles
Lower leg muscles

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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. This means 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 their hand.

Early symptoms may include:

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 health care provider may ask if there is a family history of myotonia congenita.

Tests include:

Treatment

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

Support Groups

Support Groups

The following resources can provide more information on myotonia congenita:

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.

Some people experience the opposite effect (paradoxical myotonia) and get worse with movement. Their symptoms may improve later in life.

Possible Complications

Complications may include:

When to Contact a Medical Professional

Call your 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.

Related Information

Autosomal dominant
Autosomal recessive
Aspiration pneumonia

References

Bharucha-Goebel DX. Muscular dystrophies. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 627.

Kerchner GA, Ptácek LJ. Channelopathies: episodic and electrical disorders of the nervous system. In: Daroff RB, Jankovic J, Mazziotta JC, Pomeroy SL, eds. Bradley's Neurology in Clinical Practice. 7th ed. Philadelphia, PA: Elsevier; 2016:chap 99.

Selcen D. Muscle diseases. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 393.

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Review Date: 2/4/2020  

Reviewed By: Amit M. Shelat, DO, FACP, FAAN, Attending Neurologist and Assistant Professor of Clinical Neurology, Stony Brook University School of Medicine, Stony Brook, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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