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Myotonia Congenita

By

Michael Rubin

, MDCM, Weill Cornell Medical College

Last full review/revision Jul 2020| Content last modified Jul 2020
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Myotonia congenita is an inherited disorder causing muscle stiffness and hypertrophy beginning during childhood. There are 2 main types with different modes of inheritance and manifestations.

Myotonia refers to delayed relaxation after muscle contraction, which can cause muscle stiffness.

There are two forms of myotonia congenita, Thomsen disease and Becker disease, both of which involve the same gene, CLCN1. Thomsen disease is autosomal dominant and manifests from infancy to 2 to 3 years of age. Becker disease is more common, is autosomal recessive, has a later onset from 4 to 12 years of age, and tends to be more severe than the autosomal dominant form.

Myotonia congenita should not be confused with congenital myotonic dystrophy, a separate disorder.

Symptoms and Signs

In children with myotonia congenita, there is delayed relaxation after muscle contraction, which can cause muscle stiffness. Parents describe weakness or clumsiness in their children, as well as stiffness. Myotonic symptoms lessen with age but do not disappear, and they are most noticeable after a period of rest. Patients typically have hypertrophy of the skeletal muscles due to the sustained muscle activity and the increased muscle bulk gives them an "athletic" appearance.

In Thomsen disease, onset is in infancy or early childhood and begins in the upper limbs and face, whereas in Becker disease it begins later in childhood in the lower limbs, and has more pronounced muscle hypertrophy. There is no weakness in Thomsen disease, but Becker disease is associated with transient weakness after prolonged rest and sometimes with progressive weakness.

Diagnosis

  • Electromyography (EMG)

  • Muscle biopsy

  • Genetic analysis

EMG is often done and, sometimes, muscle biopsy. Genetic analysis can reveal abnormalities in the gene causing both the autosomal dominant and the autosomal recessive forms.

Treatment

  • Physical therapy and rehabilitation

  • Sometimes drugs to decrease stiffness

Treatment of myotonia congenita is primarily symptomatic and supportive. Sometimes, drugs may be used to decrease muscle stiffness and other symptoms associated with myotonia.

More Information

The following are English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
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