Duchenne Muscular Dystrophy

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Introduction

Duchenne's muscular dystrophy (DMD) is a genetic condition which affects the muscles, causing muscle weakness. It is a serious condition which starts in early childhood. The muscle weakness is not noticeable at birth, even though the child is born with the gene which causes it. The weakness develops gradually. It usually shows up in early childhood. Symptoms are mild at first, but increase as the child gets older.

It is one of more than 20 types of muscular dystrophy. All the muscular dystrophies are caused by faults in genes (the units of inheritance that parents pass on to their children) and they cause progressive muscle weakness because muscle cells break down and are gradually lost. The Duchenne type affects only boys (with extremely rare exceptions) and a problem in this gene is known to result in a defect in a single important protein in muscle fibres called dystrophin. It is named after Dr Duchenne de Boulogne who worked in Paris in the mid-19th century who was one of the first people to study the muscular dystrophies.

Clinically Relevant Anatomy

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Mechanism of Injury / Pathological Process

The cause is a genetic change which affects the muscles. Muscles contain a protein (chemical) called dystrophin, which is necessary for muscles to function properly. People with DMD have a shortage of dystrophin in their muscles. The lack of dystrophin leads to muscle fibre damage and a gradual weakening of the muscles. The shortage of dystrophin is caused by a faulty gene.

Clinical Presentation

The muscle weakness is mainly in the 'proximal' muscles, which are those near the trunk of the body, around the hips and the shoulders. This means that fine movements, such as those using the hands and fingers, are less affected than movements like walking.

The symptoms usually start around age 1-3 years, and may include:

• Difficulty with walking, running, jumping and climbing stairs. Walking may look different with a 'waddling' type of walk. The boy may be late in starting to walk (although many children without DMD also walk late).
• When you pick the child up, you may feel as if he 'slips through your hands', due to looseness of the muscles around the shoulder.
• The calf muscles may look bulky, although they are not strong.
• As he gets older, the child may use his hands to help him get up, looking as if he is 'climbing up his legs'. This is called 'Gower's sign'.
• Some boys with DMD also have a learning difficulty. Usually this is not severe.
• Sometimes, a delay in development may be the first sign of DMD. The child's speech development may also be delayed. Therefore, a boy whose development is delayed, may be offered a screening test for DMD. However, DMD is only one of the possible causes of developmental delay - there are many other causes not related to DMD.
  

Diagnostic Procedures

The diagnosis may be suspected because of the child's symptoms (above). When looking for signs of DMD, it is important to watch the child running and getting up from the floor - the muscle weakness is more noticeable during these activities.

Tests are needed before DMD can be diagnosed. The first step in making the diagnosis is a blood test. This tests for creatine kinase. Children with DMD always have a very high level of creatine kinase (about 10-100 times normal). Therefore if a child's creatine kinase level is normal, then DMD is ruled out. If the creatine kinase level is high, further tests are needed to see whether this is due to DMD or to some other condition.

The next step in diagnosing DMD involves either a muscle biopsy and/or genetic tests:

1. A muscle biopsy involves taking a small sample of a muscle, under local anaesthetic. The sample is examined under a microscope using special techniques to look at the muscle fibres and the dystrophin protein.
2. Genetic tests are done using a blood sample. The DNA in the blood is tested to look at the dystrophin gene. This test can diagnose most cases of DMD.
   

Outcome Measures

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Management / Interventions

There is no cure for DMD at present. The proactive symptom-based multidisciplinary team (MDT) management and access to non-invasive ventilation have enabled improved survival into adulthood.

Preschool age

Usually, at this stage, the child will be well and not need much treatment. What you will usually be offered is:

• Provide information about DMD and patient support groups.
  
• Referral to a specialist team (for example, a paediatrician or neurologist, physiotherapist and a specialist nurse) to monitor child health.
• Advice about the right level of exercise.
• Genetic advice for the family.

Age 5-8 years

At this age, some support may be needed for the legs and ankles. For example, using night time ankle splints, or with a lknee-ankle-foot orthosis.

Treatment with corticosteroids can help to maintain the child's muscle strength. This involves taking medication such as prednisolone or deflazacort as a long-term treatment, either continuously or in repeated courses.

8 years-late teenage years

At some time after the age of 8 years, the child's leg muscles become significantly weaker. Walking gradually gets more difficult, and a wheelchair is needed. The age at which this happens varies from person to person. Often it is around age 9-11 years, although with corticosteroid treatment, some boys can walk for longer.

After the child starts needing a wheelchair, this is also the time that complications tend to begin, so it is important to monitor the boy's health and to treat any complications early.

Practical support and equipment will be needed at this stage, for example, wheelchairs and adaptations to the child's home and school.

Counselling and emotional support for child and family may be helpful.

Late teenage years-twenties

At this stage, muscle weakness becomes more problematic. Increasing help and adaptations are needed. Complications such as chest infections are likely to increase, so more medical monitoring and treatment are required.

Complications

Anaesthetics

People with DMD need extra care if they have a general anaesthetic. Certain anaesthetic medicines can cause a harmful reaction for people who have DMD. Also, extra care for the chest and breathing is needed. It is important to have a pre-operative assessment and a senior anaesthetist providing the anaesthetic care. Always tell doctors and nurses that you/your child has DMD.

Osteoporosis

People with DMD may develop osteoporosis (thinning of the bones). This is due to lack of mobility and also to steroid treatment. It is important to prevent osteoporosis as far as possible. A good intake of vitamin D and calcium helps keep bones strong. These can be obtained from certain foods or from vitamin supplements, and by action of sunshine on the skin (which makes natural vitamin D).

Sometimes a blood test to check your vitamin D levels is advised, and vitamin D supplements may be offered. See separate leaflet called 'Vitamin D Deficiency' for more detail.

Osteoporosis which is problematic can also be treated with certain medications, for example with 'bisphosphonates'.

Joint and spinal complications

Muscle weakness can result in some joints becoming tight - this is called a 'contracture'. In DMD, it is often the ankle joint and Achilles' tendon which become tight. This can be treated either using orthotic devices (splints or casts) or by surgical release of the tendon.

Curvature of the spine (scoliosis) can occur due to muscle weakness. Usually this happens sometime after the child needs a wheelchair. The scoliosis can cause discomfort and is not helpful for posture and breathing. Treatments which can help are a spinal brace, or surgery to the spine.

Nutrition and digestion

Some children with DMD are prone to being overweight, especially if taking steroid treatment. Teenagers and adults with DMD may be underweight, due to loss of muscle bulk. Dietary advice can be helpful in these situations.

Constipation can be a symptom for anyone who is not mobile. This can be treated with laxatives and a high fibre diet.

In the later stages of DMD (as a young adult and older), people with DMD may have difficulty with chewing and swallowing food. They may need a careful assessment and nutritional advice or supplements. If the problem is severe, then a 'gastrostomy' (a feeding tube into the stomach) may be needed.

Chest and breathing complications

During the teenage years, the breathing muscles weaken, causing shallow breathing and a less effective cough mechanism. This can lead to chest infections, because mucus and bacteria are not cleared so easily from the chest. It is important to treat chest infections promptly, for example by getting medical advice early and taking antibiotics where needed. Also, you will be offered immunisation with influenza and pneumococcal vaccines, to help prevent chest infections. Physiotherapy can help to clear mucus from the chest.

As the breathing muscles get weaker, oxygen levels in the blood may be reduced, more so while sleeping. Because this develops gradually, the symptoms may not be obvious. Possible symptoms are tiredness, irritability, morning headaches, night time waking and vivid dreams.

Breathing problems can be helped in various ways. There are techniques to assist breathing and coughing which can be taught by a physiotherapist. Also, various types of equipment can be used to assist breathing. Often, what helps is a method called 'non-invasive ventilation'. This uses a mask worn over the mouth or nose and delivers air which is pressurised. The extra air pressure compensates for the breathing muscles' weakness. Non-invasive ventilation can often be used in a way which does not interfere too much with other activities, for example, it may only be needed at night or intermittently. The equipment can be portable.

There are various other methods to help improve breathing and oxygen levels.The aim is to find the one most suited to each individual.

It is helpful if breathing problems are detected and treated early; so patients with DMD will usually be offered regular 'lung function tests' once they start to have significant muscle weakness. These are simple tests which can monitor the strength of the breathing muscles and the level of oxygen in the blood.

In the later stages of DMD, the muscle weakness progresses, and more support will be needed for breathing. This type of treatment has improved over recent years, which has helped to improve the quality of life and outlook people with DMD.

Cardiac (heart) complications

Teenagers and adults with DMD may develop a heart problem called cardiomyopathy, which means weakness of the heart muscle. With DMD, the cardiomyopathy does not usually cause much in the way of symptoms. Possible symptoms are tiredness, leg swelling, shortness of breath or an irregular heart beat. Cardiomyopathy can be helped by medication. This treatment seems to work best if started at an early stage, before symptoms are noticed. So people with DMD are usually offered regular heart check-ups, starting from early childhood. The check-ups usually involve an ECG (recording of the heartbeat) and 'echocardiogram' or 'echo', which is an ultrasound of the heart.

Differential Diagnosis

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Key Evidence

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Resources

Duchenne Muscular Dystrophy Factsheet(pdf)

Diagnosis and management of Duchenne muscular dystrophy, part 1: diagnosis, and pharmacological and psychosocial management

Diagnosis and management of Duchenne muscular dystrophy, part 2: implementation of multidisciplinary care.

Case Studies

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References

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