OVERVIEW

What is myotonic dystrophy?

Myotonic dystrophy (DM) is an inherited multisystem myopathy that affects not only skeletal muscles but also multiple systems throughout the body, such as smooth muscles, eyes, the cardiovascular system, the endocrine system, the reproductive system, and the nervous system.

Its main manifestations include skeletal muscle weakness, muscle atrophy or stiffness, abnormal cardiac conduction, cataracts, infertility, etc. Diagnosis usually requires genetic testing. The disease progresses slowly, and some patients may lose their ability to work.

Currently, there are no effective treatments, and management mainly involves symptomatic and supportive care. Patients with mild symptoms generally have a better prognosis.

How common is myotonic dystrophy?

Myotonic dystrophy is the most common muscular dystrophy in adults of European descent. The global prevalence is 3–5 per 100,000, but it is very rare in China.

What are the types of myotonic dystrophy?

Myotonic dystrophy is divided into DM1 and DM2. According to European reports, the prevalence of DM1 and DM2 is similar.

• DM1 is caused by a trinucleotide (CTG) repeat expansion in the mutated DM allele and can be further classified into:

  • Congenital type: Symptoms such as bilateral facial paralysis, feeding difficulties, joint contractures, and respiratory failure are present at birth. It is a leading cause of neonatal death.

  • Childhood type: Typically occurs before the age of 10. Muscle symptoms are often accompanied by cognitive and behavioral issues such as intellectual disability, attention deficits, and organ damage.

  • Classic type: Usually develops in the teens to thirties. In addition to muscle weakness (including respiratory muscles), symptoms include muscle stiffness, cataracts, arrhythmias, and excessive daytime sleepiness. The average lifespan of these patients is often shortened.

  • Mild type: Generally occurs after age 40, with milder symptoms that usually do not affect lifespan.

• DM2 is caused by a tetranucleotide (CCTG) repeat expansion in the mutated DM allele. It typically occurs between the teens and sixties, with primary manifestations being muscle symptoms or cataracts. Its severity is usually milder than classic DM1.

Is there a relationship between the type of myotonic dystrophy and disease severity?

There is some correlation.

Generally, the greater the CTG repeat expansion, the more severe the symptoms, and the shorter the lifespan.

SYMPTOMS

What are the common manifestations of myotonic dystrophy?

The clinical manifestations of myotonic dystrophy vary depending on the type, but most patients experience muscle weakness and myotonia.

• Muscle weakness most commonly occurs in facial muscles, characterized by a long, narrow face, high-arched palate, sunken cheeks, and drooping jaw. Some patients may also experience unsteady gait and frequent falls.

• Myotonia refers to abnormally slow muscle relaxation after normal contraction, such as difficulty releasing a clenched fist. Patients often report stiffness in hand and finger muscles.

• Other manifestations include:

  • Muscle pain.
  • Cardiac abnormalities such as arrhythmias or heart block.
  • Respiratory symptoms like weak breathing or respiratory failure.
  • Sleep disorders such as excessive daytime sleepiness.
  • Endocrine abnormalities including insulin hypersecretion and infertility.
  • Gastrointestinal symptoms like abdominal cramps, constipation, or diarrhea.
  • Cognitive impairments such as intellectual disability or poor concentration.
  • Lens opacities including cataracts.
  • Immune system issues like hypogammaglobulinemia.

How does myotonic dystrophy progress?

Myotonic dystrophy progresses relatively slowly. Most patients may require a wheelchair or become bedridden 15-20 years after onset, with some gradually losing work capacity due to muscle atrophy and cardiopulmonary complications.

Death often results from secondary pulmonary infections, heart block, or heart failure. However, mild cases (such as DM2) may remain stable long-term without reduced lifespan.

What severe consequences can myotonic dystrophy cause?

Myotonic dystrophy (primarily DM1) can lead to cognitive impairment, physical disability, increased tumor risk, and death from pulmonary or cardiac complications.

Additionally, earlier onset typically correlates with more severe symptoms.

CAUSES

Why do people develop myotonic dystrophy?

Myotonic dystrophy is a genetic disorder associated with gene mutations, such as abnormal repeat expansions of trinucleotide (CTG) or tetranucleotide (CCTG).

Specifically, there are two main forms of myotonic dystrophy, with the following causes:

• DM1, also known as Steinert disease, is caused by cytosine-thymine-guanine (CTG) trinucleotide repeat expansions in the 3' untranslated region of the myotonic dystrophy protein kinase gene located on chromosome 19q13.3.

• DM2, discovered in 1994, is a less severe condition than DM1 and is caused by cytosine-cytosine-thymine-guanine (CCTG) tetranucleotide repeat expansions in intron 1 of the ZNF9 gene (also called CNBP gene) located on chromosome 3q21.3.

Is myotonic dystrophy related to tumors?

Myotonic dystrophy is associated with an increased risk of tumors, particularly endometrial cancer, brain tumors, ovarian cancer, and colon cancer.

Is myotonic dystrophy hereditary? How is it inherited?

Yes, it is hereditary.

• If a father or mother carries a mutated gene with 35-49 CTG repeats (asymptomatic) or has clinical symptoms with ≥50 CTG repeats, there is a 50% chance the mutation will be passed to the next generation.

• The number of CTG repeats inherited may not match the parent's count; longer CTG repeats may be passed on, potentially leading to earlier onset and more severe symptoms in the next generation.

• If inherited from the father, clinical manifestations between generations show minimal differences, as fetal CTG repeats tend to remain stable or decrease. If inherited from the mother, the differences may be significant, as fetal CTG repeats may increase.

DIAGNOSIS

How to Diagnose Myotonic Dystrophy?

Most patients with myotonic dystrophy can be preliminarily diagnosed by doctors based on clinical symptoms, followed by confirmation through genetic testing.

In some cases, electromyography (EMG) and other tests such as blood tests, muscle biopsy, electrocardiogram (ECG), and ophthalmologic examinations may also be required to further assist in diagnosis or rule out other suspected conditions.

What Is Electromyography (EMG)?

Electromyography involves inserting thin needles into muscles and transmitting mild electrical currents to observe the amplitude and frequency of the electrical signals, thereby determining the presence and severity of myotonia.

Which Diseases Can Myotonic Dystrophy Be Easily Confused With? How to Differentiate Them?

Myotonic dystrophy may be confused with other hereditary distal myopathies (without myotonia). Other hereditary distal myopathies lack the clinical manifestations of myotonia. Doctors can differentiate them based on clinical features, muscle biopsy, and genetic testing.

TREATMENT

Which department should I visit for myotonic dystrophy?

Since myotonic dystrophy can affect multiple systems throughout the body, you may need to consult different departments depending on your symptoms, such as cardiology, ophthalmology, endocrinology, pediatrics, or neurology.

Can myotonic dystrophy resolve on its own?

No, it cannot resolve on its own. Symptoms do not disappear over time and may even gradually worsen.

How should myotonic dystrophy be treated?

Currently, there is no treatment to improve the condition of myotonic dystrophy. Management mainly focuses on symptomatic relief, often requiring a multidisciplinary team. Key treatment measures include:

• For muscle weakness: A multidisciplinary assessment is needed to determine if assistive devices (e.g., ankle-foot orthotics, walkers, wheelchairs, neck braces, or eyelid supports) are necessary to alleviate symptoms.

• For muscle pain: Ibuprofen combined with gabapentin may be used when needed. Tricyclic antidepressants (e.g., amitriptyline, doxepin) or low-dose corticosteroids can also be considered.

• For myotonia: Sodium channel blockers like phenytoin or mexiletine may be effective.

• For cardiac issues: A pacemaker may be considered for patients with severe problems.

• For cataracts: Corrective surgery is recommended if symptoms affect daily life.

• Rehabilitation therapy may help improve muscle weakness and maintain muscle function.

Can muscle training improve weakness in myotonic dystrophy patients?

There is currently no evidence that muscle training can improve or worsen muscle weakness. Since exercise may trigger severe arrhythmias, low-intensity training may be considered for patients with normal ECG and no cardiac symptoms, provided it is tolerable and does not cause excessive physical stress. However, patients with cardiac symptoms or abnormal ECG should first undergo clinical evaluation by a cardiologist.

Can myotonic dystrophy be completely cured?

Myotonic dystrophy cannot be completely cured. There is no effective treatment to alter the disease course, and management is limited to symptomatic relief.

DIET & LIFESTYLE

What should patients with myotonic dystrophy pay attention to in their diet?

In terms of diet, pay attention to food hygiene and avoid spicy, raw, cold, and greasy foods. Eat more nutritious foods to ensure nutritional and water-electrolyte balance and enhance the body's resistance. If swallowing difficulties occur, provide liquid or semi-liquid diets.

What should patients with myotonic dystrophy pay attention to in daily life?

In daily life, avoid catching colds. For patients with mobility difficulties or long-term bed rest, maintain personal hygiene to prevent bedsores. For mild cases, appropriate muscle training may be beneficial for the condition.

Do patients with myotonic dystrophy need follow-up examinations? How?

Patients with myotonic dystrophy should regularly visit the hospital as advised by their doctor to check heart function, lung function, and eye-related issues. Address any problems promptly if they arise.

How to care for a family member with myotonic dystrophy?

Patients with myotonic dystrophy often experience low self-esteem. As family members, do not give up on or resent the patient. Help them develop a positive treatment mindset. Encourage every small progress in treatment to strengthen their confidence in facing the disease.

Communicate frequently with the patient to alleviate their anxiety and loneliness. Assist them in gaining basic daily social skills to reduce inconveniences caused by cognitive or communication impairments.

PREVENTION

Can myotonic dystrophy be prevented? How to prevent it?

Myotonic dystrophy is a genetic disease and cannot be prevented. However, DNA analysis of fetal cells during pregnancy can be performed for prenatal testing, especially for symptomatic parents who require testing.

How to prevent complications of myotonic dystrophy?

To prevent complications of myotonic dystrophy, pay close attention to changes in the patient's condition during treatment and care. Seek immediate medical attention for any cardiopulmonary abnormalities. Focus on daily care, avoid colds, and for bedridden patients with mobility issues, ensure regular repositioning to prevent pressure sores.