Myotonic dystrophy (DM) is a type of muscular dystrophy, which is a group of genetic disorders. DM is the most common type of muscular dystrophy in adults. Symptoms usually appear in your twenties or thirties, but they can occur at any age. Myotonic dystrophy causes muscle wasting and weakness that worsens over time. These symptoms can make it difficult for your muscles to relax after grabbing or holding something.
At least 1 in 8,000 people worldwide have myotonic dystrophy. In most geographic and ethnic groups, more people have myotonic dystrophy type 1 than myotonic dystrophy type 2. But experts have recently found that type two may be just as common as type one in Germany and in Finland.
What are the symptoms of myotonic dystrophy?
There are two main types of myotonic dystrophy:
Myotonic dystrophy type 1. Mutations in the DMPK gene cause this form of DM. Researchers believe that the DMPK gene protein affects communication within cells. It could play a role in the functioning of your heart, skeletal muscles, and brain, all of which are involved in movement.
There are two forms of myotonic dystrophy type one. There is a benign form (which is usually present in mid to late adulthood) and a congenital form (which usually begins at birth). In mild myotonic dystrophy type 1, the symptoms are usually less intense.
With the congenital form, people may have low muscle tone, breathing problems, clubfoot (an inward and upward rotation of the foot), intellectual disability, or developmental delay. Some of these symptoms could be fatal.
Myotonic dystrophy type 2. Changes in the CNBP gene lead to myotonic dystrophy type two. The protein made from the CNBP gene tends to be found 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. Part of the DNA of genes repeats too often. This creates an unstable part. The gene that has this part then makes an abnormally long messenger RNA (the blueprint of the gene). This then causes problems with many other proteins. Eventually, it could stop the normal functioning of your muscle and tissue cells.
In myotonic dystrophy type 1, this process will occur in the DMPK gene. With myotonic dystrophy type two, this will occur in the CNBP gene.
Although these two forms are similar, the symptoms of myotonic dystrophy type two are usually less severe than those of type one. Both forms include:
- Myotonia (prolonged muscle contractions)
- Speech disorders
- Temporary jaw lock
- Cataracts (clouding of the lens of the eye)
- Cardiac conduction defects (defects in the electrical signals that control your heartbeat)
The muscle weakness in myotonic dystrophy type 1 tends to affect the muscles furthest from the center of your body. Experts call these muscles distal. They include the lower legs, face, neck and hands.
Myotonic dystrophy type 1 can also cause difficulty swallowing, constipation, or gallstones. If you have a uterus, the muscles in it may also act abnormally because of your DM. This could lead to complications during pregnancy and labor.
In type two, the muscle weakness usually affects the muscles 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 experienced in neuromuscular disorders can often diagnose it through a physical exam. They will look for any pattern 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 place a small needle into your muscle. They will study the electrical activity of the muscle.
A genetic test. Your doctor will evaluate certain cells in your blood and check if they have mutations in the CNBP or DMPK gene.
How do doctors treat myotonic dystrophy?
There are no treatments that can fix myotonic type one or two. Current treatment focuses on symptom management and disability control. Your doctor may want to treat symptoms such as:
Myotonia. Your doctor may suggest mexiletine (Mexitil) to combat this symptom.
Pain. Your doctor might recommend over-the-counter medications to treat DM-related pain. This may include nonsteroidal anti-inflammatory drugs, gabapentin (Gralise, Horizant, Neurontin, Gabarone), tricyclic antidepressants, mexiletine, and low-dose glucocorticoids, such as oral prednisone. In addition to medication, you can also try hot baths, massage, or heating pads.
Muscular weakness. For this symptom, your doctor may suggest that you use assistive devices like walking aids, scooters, or wheelchairs.
Weakness of respiratory muscles and cough. They can pump air into our lungs at night with a little tool called a bilevel positive airway pressure (BiPAP) machine. You can also use a cough assist device or assisted coughing techniques to alleviate this symptom.
Cataracts. Your doctor can surgically remove cataracts if they interfere with your daily life.
Cognitive and behavioral disorders. Neuropsychologists, special education help, and counseling can help with this symptom. Medications might also increase your attentiveness and ability to be alert.
Daytime fatigue. To combat this, your doctor may suggest the medications methylphenidate (Ritalin) and modafinil (Provigil). You can also adopt a better sleep schedule to alleviate this symptom.
Gastrointestinal dysfunction. If you have swallowing or digestion problems, your doctor might recommend laxatives, enemas, or suppositories. They can also help you create a defecation schedule.
Heart problems. If you have an abnormal heart rhythm due to myotonic dystrophy, your doctor may suggest a pacemaker, implantable defibrillator, or medication. They can also treat other heart problems that might be present from your DM.
Insulin resistance. You may need medication to lower your blood sugar.
In the case of surgery, it is very important for doctors to be careful with anesthesia in people with mytonic dystrophy. There is a high rate of complications from general anesthesia and even death in people with mytonic dystrophy type one.
Be sure to let your entire medical team know that you have DM. This will allow them to take precautions.
Also, doctors may wish to use succinylcholine (a skeletal muscle relaxant) in addition to anesthesia. Your doctors should avoid using it if you have myotonic dystrophy because it can cause muscle twitching.
What is the outlook for myotonic dystrophy?
Everyone’s illness will be slightly different, but usually your symptoms get progressively worse. The life expectancy of people with congenital myotonic dystrophy type 1 and classic (adult) myotonic dystrophy type 1 is generally lower.
But when mytonic dystrophy type 1 begins before adolescence, the disease may be different. Once a child survives congenital myotonic dystrophy type 1, their symptoms usually begin to improve. But they may still have cognitive problems, speech delay, difficulty eating and drinking, and other developmental issues.
Typically, type two mytonic dystrophy has a better outlook than type one. Symptoms are usually not as severe and tend to worsen more slowly.