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What Is Myotonic Dystrophy (DM)?

Medically Reviewed by Neha Pathak, MD on April 13, 2022

Myotonic dystrophy (DM) is a type of muscular dystrophy, which is a group of genetic disorders. DM is the most common kind of muscular dystrophy in adults. Symptoms usually show up around your 20s or 30s, but they can happen at any age. Myotonic dystrophy causes muscle wasting and weakness that gets worse over time. These symptoms can make it hard to relax your muscles after gripping or holding something.

At least 1 out of 8,000 people worldwide have myotonic dystrophy. In most geographic and ethnic groups, more people have myotonic dystrophy type one than myotonic dystrophy type two. But experts recently found that type two may be just as common as type one in Germany and Finland.

What Are the Symptoms of Myotonic Dystrophy?

There are two main types of myotonic dystrophy:

Myotonic dystrophy type one. Mutations in the DMPK gene cause this form of DM. Researchers believe the protein in the DMPK gene affects communication within cells. It might play a role in the function of your heart, skeletal muscles, and brain – which are all involved in movement.

There are two forms of myotonic dystrophy type one. There’s a mild form (which is usually present in mid to late adulthood) and a congenital form (which usually begins at birth). In mild myotonic dystrophy type one, symptoms are usually less intense.

With the congenital form, people may have weak muscle tone, breathing problems, clubfoot (an inward and upward turning of their foot), intellectual disability, or delayed development. Some of these symptoms could be fatal.

Myotonic dystrophy type two. Changes in the CNBP gene lead to myotonic dystrophy type two. The protein made from the CNBP gene tends to be in your heart and skeletal muscles. Here, it helps control the role of other genes in your body.

Changes in the structure of either of these genes cause DM. A part of the genes’ DNA repeats too many times. This creates an unstable piece. The gene that has this part then makes an abnormally long messenger RNA (the blueprint of the gene). This then causes issues with a lot of other proteins. Eventually, this could stop the normal function of your muscle and tissue cells.

In myotonic dystrophy type one, this process will happen in the DMPK gene. With myotonic dystrophy type two, it will happen in the CNBP gene.

While these two forms are similar, the symptoms of myotonic dystrophy type two are usually less severe than type one. Both forms include:

  • Myotonia (lengthy muscle contractions)
  • Slurred speech
  • Temporary jaw lock
  • Cataracts (clouding in the lens of your eye)
  • Cardiac conduction defects (defects in the electrical signals that control your heartbeat)
  • Diabetes

Muscle weakness in type one myotonic dystrophy tends to affect muscles that are the farthest away from the center of your body. Experts call these distal muscles. They include your lower legs, face, neck, and hands.

Myotonic dystrophy type one can also cause you to have trouble swallowing, constipation, or gallstones. If you have a uterus, the muscles in it may also act abnormal from your DM. This could lead to complications in pregnancy and labor.

In type two, muscle weakness typically affects muscles that are closer to the center of your body, or the proximal muscles. You may notice weakness in your neck, elbows, hips, and shoulders.

How Do Doctors Diagnose Myotonic Dystrophy?

Doctors with experience in neuromuscular disorders can often diagnose it with a physical exam. They’ll look for any patterns of muscle wasting, weakness, and myotonia.

They can confirm a diagnosis with lab tests. These may include:

Electromyography (EMG). In this test, your doctor will put a small needle into your muscle. They’ll study the electrical activity of the muscle.

A genetic test. Your doctor will assess certain cells in your blood and check if they have any mutations in the CNBP or DMPK gene.

How Do Doctors Treat Myotonic Dystrophy?

There aren’t any treatments that can fix Myotonic type one or two. The current treatment focuses on symptom management and disability control. Your doctor may want to treat symptoms like:

Myotonia. Your doctor may suggest mexiletine (Mexitil) to combat this symptom.

Pain. Your doctor might recommend over-the-counter medications to address and DM-related pain. This might include nonsteroidal anti-inflammatory drugs, gabapentin (Gralise, Horizant, Neurontin, Gabarone), tricyclic antidepressants, mexiletine, and low-dose glucocorticoids, like oral prednisone. Along with medication, you can try warm baths, massages, or heating pads as well.

Muscle weakness. For this symptom, your doctor may suggest that you use assistive devices like walking aids, scooters, or wheelchairs.

Breathing and coughing muscle weakness. They can pump air into our lungs at night with a small tool called a bilevel positive airway pressure (BiPAP) device. You can also use a cough assistance machine or assisted cough techniques to ease this symptom.

Cataracts. Your doctor can surgically remove cataracts if they mess with your daily life.

Cognitive and behavior issues. Neuropsychologists, special education assistance, and counseling can help with this symptom. Medications could also heighten your attention and ability to be alert.

Daytime fatigue. To combat this, your doctor may suggest medications methylphenidate (Ritalin) and modafinil (Provigil). You can also adopt a better sleep schedule to lessen this symptom.

Gastrointestinal dysfunction. If you have issues with swallowing or digestion, your doctor might recommend laxatives, enemas, or suppositories. They may also help you create a bowel schedule.

Cardiac problems. If you have an abnormal heart rhythm from myotonic dystrophy, your doctor may suggest a pacemaker, an implantable defibrillator, or medication. They can also treat other heart issues that might be present from your DM.

Insulin resistance. You may need medication to lower your blood sugar.

In the case of surgery, it’s very important that doctors be cautious with anesthesia in those with mytonic dystrophy. There’s a high rate of general anesthesia complication and even death for those with mytonic dystrophy type one.

Make sure to let your entire medical team know that you have DM. This will allow them to take precautions.

Also, doctors may want to use succinylcholine (a skeletal muscle relaxant) alongside anesthesia. Your doctors should avoid use of this if you have myotonic dystrophy since it can cause muscle contractions.

What’s the Outlook for Myotonic Dystrophy?

Everyone’s disease will differ slightly, but generally your symptoms will worsen gradually. The life expectancy for people with congenital myotonic dystrophy type one and classic (adult-onset) myotonic dystrophy type one is typically lower.

But when mytonic dystrophy type one begins before adolescence, the disease may be different. Once a child survives congenital-onset myotonic dystrophy type one, their symptoms usually begin to improve. But they still may have cognitive issues, delayed speech, trouble eating and drinking, and other development issues.

Typically, mytonic dystrophy type two has a better outlook than type one. The symptoms usually aren’t as severe, and they tend to worsen slower.

Show Sources

SOURCES:

MedlinePlus: “Myotonic dystrophy.”

The Muscular Dystrophy Association: “Myotonic Dystrophy (DM).”

National Center for Advancing Translational Sciences: “Myotonic dystrophy type 2.”

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