Muscular dystrophy

• Muscular dystrophy (MD) refers to a group of genetic diseases associated with progressive weakness and loss of muscle mass. Mutations in genes responsible for the production of proteins key to healthy muscle development (e.g. dystrophin) result in progressive muscle degeneration.
• The two most common forms of MD are:

  • Duchenne muscular dystrophy (DMD)
  • Becker muscular dystrophy (BMD)
• DMD and BMD are classic examples of X-linked recessive conditions, meaning they mostly affect males, with females acting as carriers. However, one-third of DMD cases occur as a result of spontaneous mutations
• Typical presenting features of muscular dystrophy include:

  • Progressive weakness: starting proximally and moving distally with the lower limbs being affected before the upper limbs.
  • Delayed motor milestones: typically the ability to walk independently.
  • Waddling gait
• Other presenting features of muscular dystrophy may include:

  • Faltering growth
  • Fatigue
  • Intellectual impairment (e.g. delayed speech milestones)
  • Behavioural issues: attention deficit hyperactivity disorder, autism and obsessive-compulsive disorder.
  • Leg pain
• Children may first present with delayed motor milestones, such as the inability to walk. As a result, it is important to check the creatine kinase level in children who cannot walk by 18 months of age to screen for MD.
• DMD patients usually become wheelchair users by the age of twelve. These children in particular tend to have evidence of scoliosis and poor pulmonary function
• BMD is similar to DMD, but the manifestations of BMD typically develop later and are milder. Although muscle involvement is less severe than in DMD, cardiac involvement is often a predominant feature of the presentation in BMD. 
• Typical clinical findings of muscular dystrophy include:

  • Weakness: typically the proximal and distal leg muscles in the earlier phases of the disease.
  • Calf pseudohypertrophy: due to the accumulation of connective tissue and fat replacing muscle tissue.
  • Waddling gait: typically exacerbated when attempting to run.
  • Tip-toe walking: occurs due to shortening of the Achilles tendon.
  • Gower’s sign: the child climbs up their legs when rising from the floor.
  • Hyporeflexia or areflexia
  • Loss of the arches of the feet (i.e. flat feet)
  • Difficulty or inability to squat
• The initial investigation used to screen for muscular dystrophy is serum creatine kinase (CK),
• Definitive diagnosis is achieved via a combination of:

  • Genetic analysis: to identify known muscular dystrophy mutations.
  • Muscle biopsy: to enable analysis of the dystrophin protein.
  • Findings on clinical examination
• Other investigations which may be performed include:

  • Electromyography: myopathic changes are apparent including small polyphasic potentials.
  • ECG and echocardiography: to screen for cardiomyopathy.
  • Lung function testing: to identify restrictive lung disease secondary to muscular weakness.
• Early management encompasses the period in which the child is still walking:

  • Corticosteroids
  • Vitamin D and calcium supplements
  • Physiotherapy
  • Orthoses
  • Serial casting of ankles to prevent shortening of the Achilles tendon
• Later stage management:

  • Cardiac and respiratory surveillance