[41] Duchennes Muscular Dystrophy Flashcards
What is Duchennes muscular dystrophy (DMD)?
A severe type of muscular dystrophy
What are muscular dystrophies?
A group of muscle diseases that result in increased weakening and breakdown of skeletal muscle over time
What is the incidence of DMD?
It affects 1 in 3000-6000 male infants
What is the life expectancy of patients with DMD?
Late 20’s
What is the cause of death in most causes of DMD?
- Respiratory failure
- Associated cardiomyopathy
What is the inheritance pattern of DMD?
X-linked recessive, although about 1/3 have de novo mutations
What is the genetic abnormality in DMD?
Deletion of the gene for dystrophin
What is the role of dystrophin?
It connects the cytoskeleton of a muscle fibre to the surrounding extracellular matrix through the cell membrane
What happens when dystrophin is deficient?
There is an influx of calcium ions, a breakdown of the calcium calmodulin, and an excess of free radicals, ultimately leading to myofibre necrosis
What is the average age of diagnosis of DMD?
5 years old (but children often become symptomatic much earlier than this)
What are the clinical features of DMD?
- Waddling gait
- Language delay
- Gowers sign
- Pseudohypertrophy of calves
- Slower and clumsier than peers
What is Gowers sign?
The need to turn prone to rise
What causes pseudohypertrophy of the calves in DMD?
Replacement of muscle fibres by fat and fibrous tissue
How does DMD progress?
Progressive muscular atrophy and weakness, so no longer ambulant by 10-14 years
How common are learning difficulties in DMD?
About 1/3 of affected children have learning difficulties
How can DMD be detected on neonatal screening?
Elevated CK
What is the initial investigation for suspected DMD?
CK
What is found on CK testing in DMD?
CK level 10-100x
Is CK high from birth in DMD?
Yes
Does a normal CK at presentation exclude DMD?
Yes
How is a precise diagnosis of DMD best achieved?
By a combination of;
- Genetic analysis
- Muscle biopsy, with assay for dystrophin protein
- Clinical observation of muscle strength a function
What are the differential diagnoses for DMD?
- Other types of muscular dystrophy, particularly Becker’s muscular dystrophy
- Other myopathies
- Polymyositis
- Neurological causes of muscle weakness
Give an example of a neurological cause of muscle weakness
Spinal muscular atrophy
What does the initial management of DMD include?
- Information and support for family
- Genetic diagnosis and counselling
- Referral to specialist and MDT
