Duchenne muscular dystrophy (DMD) is the most common and most rapidly progressive muscular dystrophy, with most patients losing the ability to walk by 12 years of age and requiring ventilatory support by 25 years of age.
Before the use of cardioprotective drugs and respiratory muscle aids, respiratory complications were responsible for 80% of deaths, and cardiac complications were responsible for approximately 20%. Survival past 30 years of age is no longer rare, with 10% to 40% of patients with DMD surviving to age 40 in centres that use non-invasive means of respiratory support.
The development of acute respiratory failure, previously considered inevitable, can be preventable for most patients.
Severe scoliosis and the need for corrective surgery can be avoided, and the need for mechanical ventilation delayed, by early and aggressive use of corticosteroids.
With a few exceptions, all generalised muscle disease can be managed using the principles for managing DMD.
Muscular dystrophies are progressive, generalised diseases of muscle, most often caused by defective or specifically absent glycoproteins (e.g., dystrophin) in the muscle membrane. All muscular dystrophies are characterised by ongoing degeneration and regeneration of muscle fibres. The most common and rapidly progressive muscular dystrophy is Duchenne muscular dystrophy (DMD). This is X-linked and diagnosed by the finding of absent dystrophin on muscle biopsy. Other X-linked muscular dystrophies include Becker muscular dystrophy (BMD), which is characterised by diminished quantity or quality of dystrophin in muscle biopsy specimens. BMD is a milder form of DMD. Diagnosis can be confirmed using multiplex ligation-dependent probe amplification or full sequencing of the dystrophin gene. This topic will mainly discuss DMD.
History and exam
Key diagnostic factors
- presence of risk factors
- imbalance of lower limb strength
- lower extremity musculotendinous contractures
- delayed motor milestones
- calf hypertrophy
- ambulation difficulty and falls
- diminished muscle tone and deep tendon reflexes
- normal sensation
Other diagnostic factors
- Gowers' sign
- toe walking
- urinary and bowel incontinence
- mild to severe intellectual disability
- family history of DMD
- male sex
1st investigations to order
- serum creatine kinase (CK)
- genetic testing
Investigations to consider
- electromyogram (EMG)
- muscle biopsy
stage 1: ambulatory
stage 2: non-ambulant
stage 3: ventilator-supported
- Becker muscular dystrophy (BMD)
- Limb-girdle muscular dystrophies (LGMDs)
- Emery-Dreifuss muscular dystrophy
- Clinical guidance in neuropalliative care: an AAN position statement
- Diagnosis and management of Duchenne muscular dystrophy, part 3: primary care, emergency management, psychosocial care, and transitions of care across the lifespan
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