Myotonic dystrophy

Myotonic dystrophy is a genetic condition that causes muscle weakness and wasting, and the weakness gets worse over time.

The condition can affect the muscles you use to move. It often affects the electrical conduction system of the heart, the muscles used for breathing and swallowing, the bowels, the lens of the eye and the brain.

Myotonic dystrophy can cause diabetes and hormonal changes such as thyroid problems. The reproductive system can be affected too, in both males and females. Some people have personality and behavioural problems.

In some rare cases, there is a higher chance of developing tumours.

In myotonic dystrophy, the smaller muscles are usually affected first, such as those in the hands, face and jaw, along with the muscles in the neck. Symptoms can appear at any time between birth and old age.

Other symptoms can include:

• muscle stiffness (myotonia)
• clouding of the eye lens (cataracts)
• a slow and irregular heartbeat (cardiac arrhythmia)
• slurred speech
• dysphagia (problems with swallowing)
• bowel problems like diarrhoea, constipation and incontinence
• behavioural and personality problems
• excessive sleepiness or tiredness

No two people with myotonic dystrophy have quite the same symptoms, and the severity differs too. The symptoms are likely to get worse very slowly. The condition may also become worse as it's passed down through the generations.

If you have a mild form with little or no symptoms, you might not experience significant disability.

Your heart rate will have to be monitored to check for changes. This is because there's a risk that the electrical impulses controlling your heartbeat travel too slowly through your heart.

Life expectancy can vary. Many people have a normal life expectancy. Those with the more severe congenital form, which is present from birth, might die at a very young age.

People whose symptoms begin as a child or teenager might have a shortened life expectancy. In many cases of myotonic dystrophy, the cause of death tends to be pneumonia, breathing problems or heart problems.

Tell every doctor or nurse you see that you have myotonic dystrophy, because it can cause problems with general anaesthesia.

There are 2 different types of myotonic dystrophy, DM1 and DM2. Type 1 is more common than type 2, and it tends to be more severe.

DM2 has similar symptoms to DM1. It causes weakness in the muscles close to the joints (proximal muscles), like in the:

• shoulders
• hips

Someone with DM2 might have cataracts or heart problems, but these are usually less severe than with DM1. Facial weakness and myotonia (difficulty relaxing the muscles) are usually mild, or not experienced at all.

Myotonic dystrophy is a dominant inherited MD, and it's normally passed on from one of your parents. With a dominant inherited MD, you only need to inherit the altered gene from one parent to be affected.

This means that if you have a child with an unaffected partner, there's still a 1 in 2 chance your child will develop the condition. Very few cases of myotonic dystrophy happen with no family history of it.

A gene mutation (change) in the DMPK gene on chromosome 19 causes myotonic dystrophy type 1. Myotonic dystrophy type 2 is caused by a gene change in a different gene, called the CNBP gene, which is found on chromosome 3.

A blood test will usually confirm the diagnosis.

Some parents or grandparents may have carried a very slight genetic change that never caused any symptoms, or that was never diagnosed. A careful and thorough study of the whole family will often show more members with the condition.

There's no cure for myotonic dystrophy, but supportive treatments can help you manage your symptoms.

If you have myotonic dystrophy, you will develop heart problems. You should have regular electrocardiograms (ECGs) to check your heart rhythm, and you'll also need an echocardiogram. A cardiologist (heart specialist) will do further tests and keep an eye on your heart. The cardiologist will prescribe medicine to help improve how your heart works.

You might have a pacemaker or an ICD (implantable cardioverter defibrillator) put in to help your heart function. It can be placed below the skin in your chest.

Your doctor might consider medicines like mexiletine to help with muscle stiffness.

If your dysphagia is mild, diet and speech therapy can sometimes help. If dysphagia is making you lose too much weight, a dietician might suggest food supplements.

If your dysphagia is severe, there's a risk of aspiration pneumonia. Using a different method of feeding can prevent this. In that case, you might need a gastrostomy. This is a minor operation to pass a tube through the front of the abdomen (tummy) directly into the stomach. It might be a PEG (percutaneous gastrostomy) or a RIG (radiographically inserted gastrostomy).

A gastrostomy makes sure you're getting enough nutrition and hydration. It lowers the chance of aspiration pneumonia, and you can still swallow small amounts of food and drink if you're able to. A PEG or RIG can be hidden under clothes.

You'll see an endocrinologist to manage your diabetes or other hormonal problems. You might also see a respiratory specialist to check your breathing muscles and how well they work.

If your chest muscles become weak, you might need a machine to help with your breathing. This can be particularly helpful while you sleep. It might also help with any daytime fatigue (sleepiness) you're having.

You might have diarrhoea, constipation or incontinence. If you do, you might see a gastroenterologist.

Exercise has been proven to help people with myotonic dystrophy. You might be referred to a specialist for:

• physiotherapy to work on muscle strength and flexibility
• physical aids like a walking stick, crutches or a wheelchair
• occupational therapy to help maintain independence

You might want to consider hospice care to help you or your child cope with the condition. The hospice can offer help like:

• counselling
• pain management
• respite