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 his 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:
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.
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Sarnat HB. Muscular dystrophies. In: Kliegman RM, Stanton BF, St Geme JW, Schor NF, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier; 2016:chap 609.
Selcen D. Muscle diseases. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 421.