Neurological disease in a child: Duchenne/Becker Muscular dystrophy Flashcards
Define Duchenne MD and Becker MD.
X-linked recessive degenerative muscle disorders, characterised by progressive muscle weakness and wasting of variable distribution and severity.
What is the difference between DMD and BMD?
DMD: Rapidly progressive form
BMD: Slowly progressive form
Explain the aetiology/risk factors of DMD.
Gene mutation on Xp21 results in the absence of dystrophin (<5% of normal). 2/3 are inherited, 1/3 are de novo mutations.
Dystrophin proteins forms part of a membrane-spanning protein complex of the muscle sarcolemma. This connects the cytoskeleton to the basal lamina.
Explain the aetiology/risk factors of BMD.
Exon deletions exist in the dystrophin gene Xp21 in 70% cases. Dystrophin levels are 30-80% of normal. Abnormal translation of the dystrophin gene produces abnormal but partially functional dystrophin.
What are risk factors of both DMD and BMD?
Family history
Explain the pathophysiology of DMD/BMD.
Variation in muscle fibre size, segmental necrosis of fibre groups. Initially, fibre regeneration occurs, but this fails and leads to loss of muscle and replacement by adipose cells and connective tissue.
Summarise the epidemiology of DMD.
1/3000 live male births
Summarise the epidemiology of BMD.
3-6/100, 000 live male births
What are the presenting symptoms of DMD?
Child appears healthy at birth. Onset of symptoms from 1-6 years with a waddling gait, toe-walking, difficulty running, climbing stairs or getting up from a seated or lying position.
By 10 years braces are required for walking, by 12 years most children are wheelchair bound. In 20% there is associated learning disability
What are the presenting symptoms of BMD?
Symptoms appear around 10 years and are a milder version of those in DMD.
What are signs of BMD/DMD?
Distribution of muscle weakens: Symmetrical pelvic and shoulder girdle weakness.
Calf muscle pseudohypertrophy: Excess adipose replacement of muscle fibres.
Gower’s sign: Child pushes hands down against thighs to overcome proximal muscle and pelvic girdle weakness to stand up from seated position on floor.
What are appropriate investigations for DMD/BMD?
Bloods: Increased CK present from birth Genetic testing.
EMG: Establishes myopathic nature; exclude neurogenic causes of muscle weakeness.
Muscle biopsy: Immunostaining for dystrophin.
Lung function: Decreased vital capacity secondary to decrease muscle strength leads to hypoventilation and atelectasis.
What is the medical management for muscular dystrophy?
Oral glucocorticoids improve muscle strength over 6 months to 2 years. Observational studies suggest improved function over 5 years.
Early aggressive management of cardiomyopathy.
Respiratory care and assisted respiration may be required at later stage.
Immunisation: Usual + pneumococcal and influenza.
Prophylactic antibiotics for children with low VC.
What is the orthopaedic management for muscular dystrophy?
Contracture correction and scoliosis repair to maintain mobility and preserve lung function. Scapular fixation.
What other management is required for muscular dystrophy?
Occupational/physiotherapy: Moderate physical exercise, mobility aids, night splints, braces and spinal support.
Education: Mainstream with support or special school for children with physical disabilities and/or learning disability.
Genetic counselling of female family members: CVS is 95% accurate.
Psychological: Support and counselling for parent and child. Respite care.
