Myotonic Dystrophy

Overview

Myotonic dystrophy is the most common form of muscular dystrophy that begins in adulthood. It is a genetic, progressive condition that causes muscles to weaken and waste over time, and it is also marked by myotonia, a delayed relaxation of muscles after they contract, so that a person may have trouble releasing their grip after a handshake.

Unlike many muscle diseases, myotonic dystrophy is a multisystem condition that can also affect the heart, eyes, hormones, and digestive and breathing systems. There are two main types, DM1 and DM2, which vary in severity and the muscles most affected. While there is no cure, ongoing care can manage symptoms and watch for complications, particularly heart rhythm problems.

Symptoms

Symptoms vary widely in severity and age of onset. Common features include:

• Muscle weakness, often starting in the face, neck, hands, forearms, and lower legs
• Myotonia: difficulty relaxing muscles, such as releasing a grip or opening the eyes after closing them tightly
• Muscle wasting and a long, thin face with drooping eyelids in some people
• Cataracts, often at a younger age than usual
• Fatigue and excessive daytime sleepiness
• Heart rhythm problems, breathing difficulties, swallowing trouble, and hormonal changes

A severe form can appear at birth (congenital myotonic dystrophy) with weakness and breathing problems in newborns.

Causes

Myotonic dystrophy is caused by a genetic change (an expanded repeat of DNA) in one of two genes, defining the two types:

• Type 1 (DM1): Caused by a change in the DMPK gene; it is the more common and often more severe form, and can include the congenital type.
• Type 2 (DM2): Caused by a change in the CNBP gene; it tends to be milder and affects muscles closer to the center of the body.

It is inherited in an autosomal dominant pattern, meaning a child of an affected parent has a chance of inheriting it. The condition can become more severe in successive generations, especially in DM1.

Risk Factors

• Having a parent with myotonic dystrophy
• A family history of unexplained muscle weakness, early cataracts, or heart rhythm problems
• Belonging to a family known to carry the genetic change

Because it is inherited, the main risk factor is family history rather than lifestyle.

Diagnosis

Diagnosis is based on the pattern of symptoms, family history, and specific tests:

• Clinical examination: Checking for muscle weakness and myotonia.
• Genetic testing: A blood test that confirms the diagnosis and identifies DM1 or DM2.
• Electromyography (EMG): Records electrical activity in muscles and can show characteristic myotonic patterns.
• Heart and eye evaluation: ECG and other heart tests, and an eye exam for cataracts, to assess the wider effects.

Treatment

There is no cure, so care focuses on managing symptoms, maintaining function, and monitoring for complications.

• Regular heart monitoring: ECGs and other tests to detect rhythm problems early, which is important because these can be serious.
• Physical and occupational therapy: To maintain mobility, strength, and daily function, often with braces or assistive devices.
• Treating specific issues: Cataract surgery, support for breathing or swallowing problems, and management of hormonal and other effects.
• Medications: Sometimes used to ease myotonia or daytime sleepiness.
• Genetic counseling: To help families understand inheritance and options.

A coordinated team of specialists usually provides the best care.

Prevention

Because myotonic dystrophy is inherited, it cannot be prevented through lifestyle. Genetic counseling can help people understand their risk of passing it on and discuss family planning options. For those already diagnosed, regular monitoring, especially of the heart, helps prevent or reduce complications, and avoiding certain anesthesia risks by informing care teams of the diagnosis before surgery is an important safety step.

When to See a Doctor

See a doctor if you have progressive muscle weakness, difficulty relaxing your grip, early cataracts, or a family history of myotonic dystrophy. Because the condition can affect the heart, seek urgent care for fainting, palpitations, chest pain, or severe shortness of breath, as heart rhythm problems can be dangerous. Anyone with myotonic dystrophy should tell their surgical and anesthesia team about the diagnosis before any operation, since they can be more sensitive to certain anesthetics.

Related Topics

Frequently Asked Questions

References

1. National Institute of Neurological Disorders and Stroke (NINDS). Myotonic Dystrophy.
2. MedlinePlus, U.S. National Library of Medicine. Myotonic dystrophy.
3. Muscular Dystrophy Association (MDA). Myotonic Dystrophy.
4. National Organization for Rare Disorders (NORD). Myotonic Dystrophy.