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.
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 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.
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
- 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.
Exams and Tests
The health care provider may ask if there is a family history of myotonia congenita.
- Electromyography (EMG, a test of the electrical activity of the muscles)
- Genetic testing
- Muscle biopsy
Mexiletine is a medicine that treats symptoms of myotonia congenita. Other treatments include:
- Quinine (rarely used now, due to side effects)
The following resources can provide more information on myotonia congenita:
- Muscular Dystrophy Association -- www.mda.org/disease/myotonia-congenita
- NIH Genetics Home Reference -- ghr.nlm.nih.gov/condition/myotonia-congenita
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.
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
When to Contact a Medical Professional
Call your provider if your child has symptoms of myotonia congenita.
Couples who want to have children and who have a family history of myotonia congenita should consider genetic counseling.
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.