Becker Muscular Dystrophy

• What is Becker muscular dystrophy?


  X-linked recessive disorder (primarily affects males)

  Characterised by a gradual, but progressive, skeletal muscle weakness & wasting

  Involves mutations in Dystrophin gene -> reduction/abnormality in dystrophin protein
• Dystrophin protein plays a vital role in maintaining muscle cell integrity & function.
• What are the RFs of Becker muscular dystrophy?


  FHx

  Male
• Pathophys - Becker muscular dystrophy 


  Non-frameshift insertion mutation in dystrophin gene (on Xp21) -> abnormal dystrophin protein but both binding sites are preserved

  Dystrophin protein is a part of a large membrane associated protein in muscle -> connects the muscle membrane to actin
• What is the classification of Becker muscular dystrophy (BMD)?


  Mild BMD

  • characterised by late onset of symptoms (usually after 30 yrs)
  • pts present with proximal muscle weakness that progresses slowly over time
  • often independent ambulation well into late adulthood

  Intermediate BMD

  • symptoms typically appear in late adolescence or early adulthood
  • progression faster than mild BMD
  • loss of ambulation between 20-30

  Severe BMD

  • resembles DMD but later onset & slower progression
  • symptoms may appear in childhood w/rapid progression
  • loss of ambulation in adolescence or early adulthood
• What are the signs & symptoms of BMD?


  Muscular cramps (often after exercise)

  Fatigue

  Learning difficulties & ADHD (rare)

  Muscle hypertrophy (commonly calves)

  Waddling gait

  Gowers' sign

  Dilated cardiomyopathy

  Arrhythmias

  Contractures
• What is Gowers' sign?


  Common early sign of BMD

  Patients use their hands & arms to 'walk up' their bodies from bent over position

  Due to weakness in the hip & thigh muscles

  
• What are the Inx of BMD?

  Obs

  Full Hx & examination

  Creatinine Kinase (CK) blood test -> typically elevated due to ongoing muscle breakdown

  Echo (assess cardiac involvement)

  Molecular genetic testing (diagnostic)

  Muscle biopsy

  Pulmonary function tests (assess resp muscle strength)
• What are the DDx of BMD?


  DMD

  Limb-girdle muscular dystrophy

  Emery-Dreifuss muscular dystrophy
• What is the management of BMD?


  Corticosteroids -> to delay muscle weakness, monitor for side effects

  Regular cardiac assessments -> due to high risk of cardiomyopathy, ACEi or beta-blockers may be used, consideration of ICDs

  Annual pulmonary function tests -> NIV may be used in later stages

  Physiotherapy -> maintain mobility & prevent contractures, orthotic devices may be used

  Dietician -> due to risk of dysphagia & weight loss

  Surgery -> spinal for progressive scoliosis, orthopaedic surgery to manage contractures & fractures