Define Duchenne Muscular Dystrophy. Describe its clinical features, investigations, management and complications.

Definition

• Duchenne muscular dystrophy (DMD) is a severe, progressive X-linked recessive muscle disorder caused by a mutation in the dystrophin gene (absent dystrophin), leading to progressive muscle degeneration.
• It affects boys.

Clinical Features

• Onset in early childhood — delayed walking, frequent falls, difficulty running/climbing stairs.
• Proximal muscle weakness; Gower's sign (using hands to 'climb up' the legs when rising).
• Calf pseudohypertrophy (fat/fibrous replacement), waddling (lordotic) gait.
• Progressive — usually wheelchair-bound by ~12 years; later cardiomyopathy and respiratory failure.

Investigations

• Markedly raised serum creatine kinase (CK).
• Genetic testing (dystrophin gene deletion) — confirmatory; muscle biopsy (absent dystrophin) if needed.

Management

• Corticosteroids — slow the decline in muscle strength and prolong ambulation.
• Multidisciplinary supportive care — physiotherapy, prevention of contractures, and cardiac and respiratory monitoring.
• Genetic counselling and carrier detection for the family.

Genetics & Carrier Detection

• X-linked recessive — affected boys, carrier mothers; ~⅓ are new mutations.
• Female carriers may have a raised CK and, occasionally, mild symptoms; offer genetic counselling and prenatal testing.

Becker Muscular Dystrophy (contrast)

Becker muscular dystrophy is caused by mutations in the same dystrophin gene but with reduced (not absent) dystrophin — it is milder, with a later onset and slower progression than DMD.

Complications

• Progressive loss of ambulation; joint contractures and scoliosis.
• Dilated cardiomyopathy and respiratory failure are the major causes of death — hence regular cardiac and respiratory surveillance.

Supportive & Multidisciplinary Care

• Physiotherapy and stretching to delay contractures; assistive devices and wheelchair when needed.
• Cardiac (echocardiography) and respiratory (lung function, night-time support) surveillance; bone health.
• Steroids to prolong ambulation, plus psychological and educational support for child and family.