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. Diagnosis is by electromyography and sometimes muscle biopsy. Treatment is primarily supportive, but membrane-stabilizing medications may be of benefit.
Myotonia refers to delayed relaxation after muscle contraction, which can cause muscle stiffness.
There are 2 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 Thomsen disease.
Myotonia congenita should not be confused with congenital myotonic dystrophy, a separate disorder.
Symptoms and Signs of Myotonia Congenita
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 of Myotonia Congenita
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 of Myotonia Congenita
Physical therapy and rehabilitation
Membrane-stabilizing medications to decrease stiffness
Treatment of myotonia congenita is primarily symptomatic and supportive.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
Muscular Dystrophy Association: Information on research, treatment, technology, and support for patients living with myotonia congenita
National Organization for Rare Disorders: Comprehensive information regarding myotonia congenita, including standard and investigational therapies and links to related topics
