What Is Myotonia Congenita?

Congenital myotonia is a musculoskeletal disease that is caused by mutations in the genetic gene and is mainly manifested by limb muscle rigidity. The clinical features are infantile onset, muscular hypertrophy, and difficulty in relaxing after contraction. According to genetic defects and clinical manifestations, the prevalence rate is about 1/100000; according to different genetic methods and clinical characteristics, it is divided into Thomsen type of autosomal dominant inheritance of chloride ion channels and Becker type of autosomal recessive inheritance. There is also congenital paramuscular rigidity associated with autosomal dominant inheritance of sodium ion channels. The prognosis of the disease is good and life span is not affected.

Basic Information

nickname

Thomsen disease

English name

Myotonia Congenita

Visiting department

Orthopedics, neurology

Common locations

Proximal limb muscles, eyelids, tongue

Common causes

Heredity

Common symptoms

Myotonia and hypertrophy

Pathogenesis of congenital myotonia

Thomsen-type and Becker-type congenital muscle rigidity are both caused by a defect in the CLCN1 gene encoding the chloride channel; congenital paramuscular rigidity is caused by a defect in the SCN4 A gene of the sodium channel skeletal muscle subtype.

Clinical manifestations of congenital myotonia

Onset age

It usually starts in infancy or childhood, and the main manifestations are muscle rigidity and hypertrophy, and the condition is generally stable. Becker-type onset is later than Thomsen-type, and the clinical manifestations are also slightly more severe.

2. Myotonia

Becker-type and Thomsen-type congenital muscle rigidity usually affects skeletal muscles throughout the body. It manifests as difficulty walking when starting, stiff limbs, awkward movements, standing awkward after sitting for a long time, and unable to relax after shaking hands. The above symptoms are alleviated after repeated exercise and worsened after rest or in a cold environment. Thumping muscles can be seen as "muscle mounds" or local muscle contractions with a short local depression, known as throbbing muscle rigidity. Sudden fright or sudden braking on a bus causes your whole body to become rigid and fall, and you cannot support it with your hands when you fall.

Congenital paramuscular rigidity mainly involves facial muscles, neck muscles, and upper limb muscles. Similar to Becker and Thomsen congenital muscle rigidity, the symptoms of muscle rigidity can also be significantly worsened when exposed to cold. So it is paramuscular rigidity or abnormal muscle rigidity.

3. Muscle hypertrophy

Becker-type and Thomsen-type congenital myotonia patients have generalized hypertrophy of their skeletal muscles, which resembles bodybuilders. Their muscle strength is greater than that of ordinary people without muscle atrophy. Hypertrophy in patients with congenital paramuscular rigidity mainly occurs in the calf of some patients, and there are few bodybuilders.

Congenital Myotonia Test

Including electromyography and genetic testing.

EMG

The electromyogram can show a typical myotonic potential, the insertion potential is prolonged, and the speaker makes a sound when the motorcycle is accelerating.

2. Genetic testing

The CLCN1 and SCN4A genes were examined.

Diagnosis of congenital myotonia

According to the clinical manifestations of the patient, combined with electromyography to detect myotonic discharge and genetic testing to detect pathogenic mutations can be a clear diagnosis. Identification of neuromuscular disease in children with muscle rigidity is required before genetic testing.

Congenital Myotonia Treatment

Congenital myotonia can be reduced in adulthood. Treatment is mainly symptomatic. Some sodium channel blockers can be used, such as mexiletine, carbamazepine, and phenytoin sodium. Avoid strenuous exercise, cold, tension and other factors that aggravate muscle rigidity, and avoid using drugs such as epinephrine that cause worsening of symptoms.

Congenital Myotonia Care

Patients should be protected from sudden position changes. Parents should give more comfort and counseling if psychological disorders occur.

Prognosis of congenital myotonia

The prognosis is good and life is not affected.

Genetic counseling for congenital myotonia

The prognosis is good and prenatal diagnosis is generally not required.