Muscular dystrophy Flashcards
Most common muscular dystrophy
Duchenne
Why is creatine kinase measured in boys with delayed walking?
Muscular dystrophy causes raised CK
What does dystrophin do?
Anchors actin and prevents excessive calcium entering sarcolemma
If dystrophin is not present or faulty, calcium enters sarcolemma and water enters the mitochondria which then bursts
Oxidate stress occurs and eventually cell death occurs, muscle fibres necrose and are replaced with adipose and connective tissue
What is Duchenne muscular dystrophy?
- X-linked recessive
- Presents in early childhood
- New mutations of the dystrophin gene are common meaning the female relatives of a child are not necessarily carriers
Epidemiology of Duchenne
1 in 3500 new-born males
Aetiology of Duchenne muscular dystrophy
- Mainly deletion mutations in dystrophin gene leading to absence or defect in the dystrophin protein causing progressive muscle degeneration
- Why does the dystrophin gene get affected so readily? Because it is a large gene
- In DMD no dystrophin is made
- In Becker’s the dystrophin is abnormal
Presentation of Duchenne muscular dystrophy
Progressive proximal muscular dystrophy with pseudohypertrophy of calves
Pseudohypertrophy occurs because the muscle tissue is replaced by fat and connective tissue
- All patients symptomatic by age 3
- Delayed motor milestones
- Cant run
- Waddling gait
- Gower’s sign – climbing up legs
- Speech delay
- FTT
- Abnormal LFTs
- Fatigue
- Malignant hyperthermia/ other anaesthetic complications
Investigations for Duchenne muscular dystrophy
Initial investigation is serum CK: In DMD the level is very high (10-100x normal)
Normal CK at presentation excludes DMD - CK eventually falls later on in the disease as muscle wasting occurs so it is not a reliable screening test for those already in wheelchairs
Precise diagnosis via:
- Genetic analysis
- Muscle biopsy
- Clinical observation of muscle strength and function
Serum CK is usually high in carriers
Differentials for Duchenne muscular dystrophy
- Becker’s
- Other myopathies
- Polymyositis
- Spinal cord lesions
Management of Duchenne
Physio to prevent contractures
Knee-foot-ankle orthoses to help prolong walking
Serial casting of ankles
Corticosteroids
- May improve muscle strength and function in the short term but balance this against risk of osteoporosis
Management of Duchenne after walking ability lost
- Independent mobility lost around age 8-11
- Wheelchairs
- Orthotics or surgery for contractures and scoliosis
- Cardiac and respiratory surveillance
- Support and adaptations for school
- Counselling
Management of Duchenne in the later stages
- Support for increasing weakness and fatigue
- Optimise cardiac and respiratory treatment
- Respite for family
- Palliative care
Complications of Duchenne
- Joint contractures
- Respiratory complications
- Respiratory failure is the most common cause of death
- Cardiac complications, dilated cardiomyopathy is common
- Gastro: pseudo obstruction
- Learning difficulty 20%
- Anaesthetic complications
Prognosis of Duchenne muscular dystrophy
- Hand muscles and extraocular muscles spared until late on
- Affected boys usually confined to wheelchair by age 12
- Death from respiratory complications in 20s or 30s
Risks for female carriers of DMD mutation
Increased risk of cardiomyopathy
- 10% lifetime risk
Manifesting carriers: 2-5% have skeletal muscle symptoms
- Aches, calf muscle enlargement, symptoms tend to progress with time
