Myotonic dystrophy is the most common type of late-developing muscular dystrophy. Although it can appear at any age, it usually presents itself in adults in their 20s and 30s. Approximately 1 in 8,000 people have myotonic dystrophy.

The condition is progressive, so symptoms of muscle stiffness and weakness tend to worsen over time. People with myotonic dystrophy typically experience extended muscle contractions and have difficulty relaxing muscles after use.

What causes myotonic dystrophy?

There are two types of myotonic dystrophy, both caused by genetic mutations. DM1 is caused by an abnormal expansion in a region of the DMPK gene;. DM2 is caused by an expansion in the CNBP gene.

These abnormally expanded regions can become even longer as the disease is passed from parent to child, so the severity of the disease can increase from one generation to the next. In certain cases, they can appear as early as just after birth, in which case the condition is called congenital myotonic dystrophy.

What are the symptoms of myotonic dystrophy?

Although symptoms of DM1 and DM2 overlap, there are some differences and DM2 usually is the milder of the two. DM1 is associated with extended muscle contraction of the lower legs, hands, neck, and face, while DM2 particularly affects the muscles of the neck, shoulders, elbows, and hips.

People with myotonic dystrophy also may develop cardiac issues, where the heart develops an abnormal rhythm (arrhythmias) as the heart muscles weaken. Similarly, the muscles that control breathing may be affected, causing problems with breathing especially during sleep.

Patients may experience issues with involuntary muscles, principally those in the gastrointestinal tract and, in women, the uterus. Constipation, gallstones, and trouble during pregnancy and labor may occur as a result. Men also may become infertile.

Cataracts also are common in myotonic dystrophy patients.

How is myotonic dystrophy diagnosed?

Physical symptoms and a family history of myotonic dystrophy are strong indicators of the disease. Electromyography, a technique used to analyze the health of muscles and the nerves that control them, can be used to diagnose the disease, but to confirm the diagnosis genetic testing is necessary to identify alterations to the DMPK and CNBP genes. Those affected by the condition also have moderately high levels of the muscle enzyme creatine kinase, and elevated levels of liver enzymes.

How is myotonic dystrophy treated?

There is no cure for myotonic dystrophy, but there are therapies available to help patients better control their symptoms. Treatment plans are tailored to specifically address the problems associated with each patient’s condition. Physiotherapy and orthopedic support devices can be of help in managing muscle weakness. Patients who experience serious symptoms may need a wheelchair to maintain mobility. Non-steroidal anti-inflammatory drugs (NSAIDs) also can be prescribed for pain.

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