Muscular dystrophy

Question 1

Define Duchenne MD and Becker MD.

Answer 1

X-linked recessive degenerative muscle disorders
Characterised by progressive muscle weakness + wasting of variable distribution + severity.

Question 2

What is the difference between DMD and BMD?

Answer 2

DMD: Rapidly progressive form

BMD: Slowly progressive form

Question 3

Explain the aetiology of DMD.

Answer 3

Mutation on Xp21 results in absence of dystrophin
2/3 are inherited, 1/3 are de novo mutations.
Dystrophin is part of a large membrane associated protein in muscle which connects muscle membrane to actin.

Question 4

Explain the aetiology/risk factors of BMD.

Answer 4

Mutation in dystrophin gene Xp21
Dystrophin levels 30-80% of normal

Question 5

What are risk factors of both DMD and BMD?

Answer 5

Family history

Question 6

Summarise the epidemiology of DMD.

Answer 6

1/5000 live male births
Peak incidence 1-5y
Average age of dx: 4.3y

Question 7

Summarise the epidemiology of BMD.

Answer 7

0.04/100, 000 live male births

Question 8

What are the progression of symptoms of DMD?

Answer 8

Child appears healthy at birth.
Onset of Sx from 1-6y with a waddling gait, difficulty running, climbing stairs
By 10y braces are required for walking
12y most are wheelchair bound. In 20% there is associated learning disability

Question 9

Describe the muscle weakness in DMD

Answer 9

Proximal muscle weakness
in a proximal to distal pattern, typically develops from 2-3y

Question 10

List 3 features of DMD that may be noticed by parents

Answer 10

Delayed motor milestones
Gait abnormalities (e.g. waddling gait) + frequent falls are common
Learning disabilities

Question 11

What are the presenting symptoms of BMD?

Answer 11

Sx appear ~10y
A milder version of those in DMD
Intellectual impairment much less common

Question 12

What are signs of BMD/DMD?

Answer 12

Distribution of muscle weakens: Symmetrical pelvic + shoulder girdle weakness.

Calf muscle pseudohypertrophy: Excess adipose replacement of muscle fibres.

Gower’s sign: Child pushes hands to floor + then “climbs up” their legs to stand up from seated position on floor.

Question 13

What are appropriate investigations for DMD/BMD?

Answer 13

Bloods: Increased CK. Confirmed with genetic testing.

EMG: Establishes myopathic nature; r/o neurogenic causes of muscle weakness.

Muscle biopsy: Immunostaining for dystrophin.

Lung function: Decreased vital capacity secondary to decrease muscle strength leads to hypoventilation + atelectasis.

Question 14

What is the medical management for muscular dystrophy?

Answer 14

MDT care
Oral Prednisolone improve muscle strength over 6 months to 2y.

Early aggressive Mx of cardiomyopathy.

Respiratory care + assisted respiration may be required at later stage.

Immunisation: Usual + pneumococcal + influenza.

Prophylactic abx for children with low VC.

Question 15

What is the orthopaedic management for muscular dystrophy?

Answer 15

Contracture correction + scoliosis repair to maintain mobility + preserve lung function.
Scapular fixation.

Question 16

What other management is required for muscular dystrophy?

Answer 16

OT/ PT: Moderate physical exercise, mobility aids, night splints, braces + spinal support.

Education: Mainstream with support or special school for physical disabilities +/or LD

Genetic counselling of female family members: CVS is 95% accurate.

Psychological: Support + counselling for parent + child. Respite care.

Question 17

What are complications associated with muscular dystrophy?

Answer 17

Loss of mobility
Limb contractures
Scoliosis
Osteoporosis
Respiratory failure
Infection
Dilated cardiomyopathy (annual echos)
SEs of long-term oral steroids.

Question 18

What is the prognosis of DMD?

Answer 18

Respiratory + cardiac failure is the main cause of death.
May now live into 30s.

Question 19

What is the prognosis of BMD?

Answer 19

Disease develops later + less rapidly. Most patients walk beyond 16y of age + may maintain this into adulthood.