Muscular Dystrophy
last authored: Oct 2009, David LaPierre
last reviewed:
Introduction
Muscular dystrophy refers to a group of diseases characterized by progressive loss of skeletal and cardiac muscle.
The Case of...
a simple case introducing clincial presentation and calling for a differential diagnosis. To get students thinking.
Causes and Risk Factors
There are a number of distinct types of MD.
Duchenne Muscular Dystrophy (DMD) affects 1:4000 males. Two-thirds of cases are X-linked recessive, while 1/3 are spontaneous mutations. It is causes by a mutation in the structural protein dystrophin, leading to muscle fibre fragility, fibre breakdown, necrosis, with repeated cycles of regeneration.
Dystrophin expression in the brain can lead to delayed motor or cognitive development. Cardiomyopathy may also be present.
Becke'rs Muscular Dystrophy is an X-linked recessive condition due to a mutation in the dystrophin gene.
Pathophysiology
A bit about dystrophin here....
History and Physical Exam
A family pedigree analysis is helpful.
DMD begins to show proximal muscle weakness by age 3.
- Gower's sign: child uses hands to walk up legs when moving from sitting to standing
- waddling gait
- toe walking
- calf hypertrophy and thigh wasting
- decreased reflexes
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
DMD shows CK 50-100x normal, as well as increased levels of lactate dehydrogenase.
Muscle biopsy
Diagnostic Imaging
EMG
Treatments
Supportive therapy is a mainstay, with physiotherapy, braces, and wheelchairs. Obesity should be prevented.
Surgery can be used to correct scoliosis.
Steroids, ie prednisone or deflazacort, can be used to control muscle damage.
Gene therapy trials continue.
Consequences and Course
DMD usually results in children being wheelchair-bound by age 12.
Early flexion contractures, scoliosis, osteopenia, and fractures often follow.
Death usually comes in the 20s or 30s following pneumonia, respiratory failure, or CHF.
Becker's follows a similar pattern, but at a slower rate. Death from respiratory failure commonly occurs in the 40's.
Resources and References
Topic Development
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