What Is Myotonic Muscular Dystrophy?

Tonic muscular dystrophy is an autosomal dominant hereditary multisystem disease characterized by progressive muscle weakness, muscular atrophy, and muscular rigidity. The disease includes type 1 caused by mutations in the tonic muscular dystrophy protein kinase gene (DMPK) and type 2 caused by mutations in the cellular nucleic acid binding protein gene (CNBP). Type 1 is the most common muscular dystrophy in adults with an incidence of approximately 1/8000 1/7000. Type 2 is rare.

Basic Information

Pathogenesis of tonic muscle dystrophy

Tonic muscle dystrophy type 1 and type 2 are related to the increase of DMPK and ZNF9 gene repeat sequences, respectively. Muscular dystrophy-like changes occur in skeletal muscle, and other systemic damages such as endocrine, heart and eye lens are also present.

Clinical manifestations of tonic muscle dystrophy

Tonic muscular dystrophy type 1 usually develops during adolescence. The first symptom is stiff muscles in the hands, manifested by the effort of loosening hands after fisting, and with the weakness of the hand muscles, facial muscle rigidity is manifested by closing the eyes forcefully and not opening the eyes quickly. With the development of the disease, forearm and hand muscle atrophy, weakness and atrophy of the calf muscles cause the foot to sag, and the toes are laborious to lift when walking. The atrophy of the facial muscles, masseter muscles, and temporal muscles leads to a long and thin face, which looks like an axe, hence the name "axe-shaped face". The weakness of the neck muscles makes it difficult to lie down in the supine position, and some patients have difficulty speaking and swallowing due to weakness and rigidity of the tongue and throat muscles.

Tonic muscle dystrophy type 2 is more common in women with relatively mild symptoms. The first symptom is weakness in the proximal limbs, followed by hand stiffness and muscle pain.

Patients with early onset are more likely to be affected by other systems. Endocrine abnormalities can be seen in diabetes, hypothyroidism and excessive sleep, men with hair loss and impotence, women with irregular menstruation, infertility or habitual abortion. In the late stage of the disease, heart damage occurs with palpitation, chest tightness and shortness of breath, and arrhythmia occurs in severe cases; cataracts in the eyes cause vision loss; gastrointestinal smooth muscle dysfunction occurs in constipation; central nerve damage causes cognitive dysfunction and depression.

Tonic muscle dystrophy test

The auxiliary tests used for diagnosis mainly include creatine kinase, electromyogram, and genetic tests. Due to multiple systemic damage, examinations of relevant organs are needed to understand the development of the disease, especially regular ECG examinations.

Enzyme inspection

Slightly elevated serum creatine kinase and lactate dehydrogenase.

2. Electromyography

A typical myotonic discharge appears in the EMG, and continuous high-frequency tonic waves gradually decay in the affected muscle, and the EMG speaker emits a motorcycle-like acceleration sound.

3 .Gene testing

Genetic testing of DMPK and CNBP genes can reveal abnormal repeats.

Diagnosis of tonic muscle dystrophy

The diagnosis was confirmed based on the patient's clinical manifestations, typical myotonic discharge electromyogram, and abnormal repeat sequences detected by genetic testing.

Tonic muscle dystrophy treatment

Myotonia can be treated with sodium channel inhibitors such as quinine sulfate, procainamide, and phenytoin. However, these drugs have an adverse effect on cardiac conduction and need to be treated with caution.

Other system damage needs to choose the appropriate treatment method according to the situation. Patients with severe atrioventricular block can choose to implant a permanent pacemaker, and cataract can be treated surgically.

Tonic muscle dystrophy care

Muscle weakness, vision loss, etc. can affect daily activities and require proper escort or help. Because serious arrhythmia and other diseases often occur, it is necessary to check the ECG regularly and treat it in time.

Prognosis of tonic muscle dystrophy

Patients with tonic muscle dystrophy interfere with work due to limb weakness, sleepiness, and cognitive impairment. Sudden death due to cardiac block or arrhythmia.

Genetic counselling for tonic muscle dystrophy

Tonic muscle dystrophy has a greater genetic risk. Genetic counseling is needed before childbirth. Prenatal diagnosis can be performed through prenatal genetic tests after pregnancy.