Duchenne Muscular Dystrophy

Question 1

What is the mode of inheritance in DMD?

Answer 1

It is an x-linked recessive disorder, although about a third have new mutations.

Which results in a deletion of the short arm on X21.

Question 2

What is the pathophysiology of DMD?

Answer 2

DMD causes there to be a deficiency in the protein dystrophin.

Dystrophin deficiency affects the intracellular pathway leading to an increased influx of Ca.

A breakdown in the Ca-calmodulin complexes and an increased no. of free radicals. These free radicals lead to myofibril necrosis.

Question 3

How do children with DMD present?

Answer 3

Its is often diagnosed between the ages of 3 -7 due to a gross motor delay.

Standing, walking and running may all be delayed.

They also demonstrate difficulty standing up Gower’s sign and climbing stairs.

They will often walk on there toes or the balls of there feet and often puff out there chest to help them balance. This gives them a waddling gait.

They will tend to struggle with balance and be clumsier than there peers.

There is also pseudohypertrophy of the calf muscles (the calf muscle is replaced with fat and connective tissue so they a appear large however are weak)

Note: Rarely can also cause learning difficulties

Question 4

What is the progression of DMD from the age of 8 onwards?

Answer 4

Between the ages of 8-14 and most will lose the ability to walk and be wheelchair bound at least part of the time.

They will also need assistance with activities involving there arms and trunk.

Scoliosis is a common complication due to weak muscles making it difficult to sit straight in their chair.

In the teen years, myocardial weakness will develop, which can cause symptoms of heart failure.

Most of those with DMD will die in there late teens or early twenties due to cardiac failure or a respiratory infection (more prone due to weak chest muscle=poor cough)

Question 5

What is Gower’s sign?

Answer 5

When asked to get up off of the floor, he will often put his rear end up in the air first and then “walk” his arms up his legs with his hands until he is standing; using his arms for supports. The medical term for this is “Gowers Maneuver.”

Question 6

What are the investigations for a patient with suspected DMD?

Answer 6

Initial investigation:

• Creatine Kinase (raised in muscle breakdown): Will be greatly raised in the 1000’s
• Muscle biopsy
• Genetic testing can also be done however it is very expensive and may give a false positive as it does not test for all the mutations which cause DMD

Question 7

What is the management for a child with DMD?

Answer 7

Scoliosis

• Appropriate exercise helps to maintain muscle power and mobility and delays the onset of scoliosis.
• Attention to maintaining a good sitting posture helps to minimise the risk of scoliosis.
• Scoliosis is managed with a truncal brace, a moulded seat and ultimately surgical insertion of a metal spinal rod.

Contractures:
-Occur particularly at the ankles, should be prevented by passive stretching and the provision of night splints.

Walking:

• Can be prolonged with the provision of orthoses (orthotic insoles).
• Lengthening of the Achilles tendon may be required to facilitate ambulation (walking/moving).
• Corticosteroids are also used as they are thought to slow the disease process and increase ambulation

Respiratory:

• CPAP machines may be helpful as nocturnal hypoxia due to weakness can be a problem.
• Physio

Cardiac:
-Need reviewing by a cardiologist

Question 8

Which medical profession is it very important to inform about DMD?

Answer 8

Anaesthetics.

Those with DMD can react badly to certain anaesthetics.

Extra care must also be taken over the neck due to weak muscles.