Understanding Myotonia congenita: Causes, Symptoms, and Management

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Myotonia congenita

by Alike Medical Team ∙ Updated on June 13, 2023

Additional names

This group contains additional names: - Thomsen disease - Generalized myotonia

General

Myotonia congenita is a congenital neuromuscular channelopathy that affects skeletal muscles. It is a genetic disorder. The hallmark of the disease is the failure of initiated contraction to terminate, often referred to as delayed relaxation of the muscles (myotonia) and rigidity. The condition is sometimes referred to as fainting goat syndrome, as it is responsible for the eponymous 'fainting' seen in fainting goats when presented with a sudden stimulus. Of note, myotonia congenita has no association with malignant hyperthermia (MH).

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Signs & symptoms

Early symptoms may include: * Difficulty swallowing * Gagging * Stiff movements that improve when they are repeated * Frequent falling * Difficulties opening eyelids after strenuous contraction or crying (von Graefe's sign) Possible complications may include: * Aspiration pneumonia (caused by swallowing difficulties) * Frequent choking or gagging in infants (also caused by swallowing difficulties) * Abdominal muscle weakness * Chronic joint problems * Injury due to falls

Diagnosis

Two types of myotonia congenita exist, an autosomal dominant form and an autosomal recessive form. Autosomal dominant myotonia congenita is also called Thomsen disease, Autosomal recessive myotonia congenita is also called generalized myotonia, recessive generalized myotonia (RGM), Becker disease, and Becker myotonia. With the advent of genetic testing, it has recently been found that some typically recessive mutations may occur in a dominant fashion in some individuals. The reason for this is not known. Because several CLCN1 mutations can cause either Becker disease or Thomsen disease, doctors usually rely on characteristic signs and symptoms to distinguish the two forms of myotonia congenita. However, myotonia caused by CLCN1 mutations can occasionally be clinically indistinguishable from myotonia caused by sodium channel mutations (SCN4A mutations) resulting in the similar disease paramyotonia congenita.

Treatment

Some cases of myotonia congenita do not require treatment, or it is determined that the risks of the medication outweigh the benefits. If necessary, however, symptoms of the disorder may be relieved with quinine, ranolazine, procainamide, flecainide, phenytoin, carbamazepine, mexiletine and other anticonvulsant drugs. Physical therapy and other rehabilitative measures may also be used to help muscle function. Genetic counseling is available.

Note

☝ We provide information on prescription and over-the-counter medicines, diagnosis, procedures and lab tests. This material is provided for educational purposes only and is not medical advice, diagnosis or treatment.

National Institutes of Health ∙ World Health Organization ∙ MedlinePluse ∙ Centers for Disease Control and Prevention

☝ All information has been reviewed by certified physicians from Alike

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