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Key Features

  • Inherited myopathic disorders

    • Characterized by progressive muscle weakness and wasting

    • Subdivided by mode of inheritance, age at onset, and clinical features (Table 24–9)

  • Duchenne muscular dystrophy

    • Due to a genetic defect on the short arm of the X chromosome

    • Affected gene codes for the protein dystrophin, which is almost absent from diseased muscles

    • Genetic defect is detectable in pregnancy

  • Becker muscular dystrophy

    • Dystrophin levels are generally normal

    • Protein is qualitatively altered

Table 24–9.Selected muscular dystrophies.1

Clinical Findings

  • Muscle weakness, often in a characteristic distribution

  • Age at onset and inheritance pattern depend on specific dystrophy

  • Duchenne dystrophy

    • Pseudohypertrophy of muscles

    • Intellectual disability

    • Skeletal deformities, muscle contractures, and cardiac involvement

Diagnosis

  • Serum creatine kinase level

    • Increased, especially in the Duchenne and Becker varieties

    • Mildly increased in limb-girdle dystrophy

  • Electromyography may confirm myopathic, rather than neurogenic, weakness

  • Histopathologic examination of muscle biopsy specimen can distinguish between various muscle diseases

Treatment

  • Eteplirsen

    • Approved for Duchenne muscular dystrophy

    • Treated patients had more functional dystrophin on muscle biopsy than controls and a slower rate of disease progression than matched historical controls

  • Prednisone (0.75 mg/kg orally daily or 10 mg/kg orally given weekly over 2 days) or deflazocort (0.9 mg/kg orally daily)

    • Improves muscle strength and function in boys with Duchenne dystrophy

    • However, side effects need to be monitored

    • Although both medications cause similar side effects, weight gain at 1 year is less with deflazacort

  • Important to encourage patients to lead as normal lives as possible

  • Prolonged bed rest must be avoided; ...

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