Myotonia congenita
Thomsen's disease; Becker's diseaseMyotonia 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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Causes
Myotonia congenita is caused by a genetic change (genetic variant). 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 type of muscle stiffness called myotonia.
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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:
- Difficulty swallowing
- Gagging
- Stiff movements that improve when they are repeated
- Shortness of breath or tightening of the chest at the beginning of exercise
- Frequent falls
- Difficulty opening eyes after forcing them closed or crying
Children with myotonia congenita often look muscular and well-developed. They may not have symptoms of myotonia congenita until age 2 or 3.
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Exams and Tests
Your health care provider may ask if there is a family history of myotonia congenita.
Tests include:
- Electromyography (EMG) and nerve conduction studies (NCS)
- Genetic testing
- Muscle biopsy
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Treatment
As cold and stress can worsen symptoms, management is first directed at avoiding these potential triggers. Some forms of exercise may also be beneficial. Mexiletine is a medicine that treats symptoms of myotonia congenita. Other treatments include:
- Phenytoin
- Procainamide
- Quinine (rarely used now, due to side effects)
- Carbamazepine
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Support Groups
The following resources can provide more information on myotonia congenita:
- Muscular Dystrophy Association -- www.mda.org/disease/myotonia-congenita
- National Library of Medicine, Medline Plus -- medlineplus.gov/genetics/condition/myotonia-congenita/
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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.
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Possible Complications
Complications may include:
- 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
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When to Contact a Medical Professional
Contact your provider if your child has symptoms of myotonia congenita.
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Prevention
Couples who want to have children and who have a family history of myotonia congenita should consider genetic counseling.
References
Bryan ES, Alsaleem M. Myotonia congenita. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024. Updated August 28, 2023. PMID: 32966006 www.ncbi.nlm.nih.gov/books/NBK562335/.
Kang MK, Kerchner GA, Ptácek LJ. Channelopathies: episodic and electrical disorders of the nervous system. In: Jankovic J, Mazziotta JC, Pomeroy SL, Newman NJ, eds. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022:chap 98.
Manzur AY. Muscular dystrophies. In: Kliegman RM, St. Geme JW, Blum NJ, et al, eds. Nelson Textbook of Pediatrics. 22nd ed. Philadelphia, PA: Elsevier; 2025:chap 649.
Selcen D. Muscle diseases. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 389.