Duchenne’s Muscular Dystrophy

Original article by Tom Leach | Last updated on 16/5/2014
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This is a severe form of muscular dystrophy, and most boys do not survive past adolescence. It is an X-linked recessive condition.
Typically affects skeletal muscles initially, but may later go on to affect the heart, and sometimes diaphragm.
 

Epidemiology

  • Affects 1 in 3500 male boys
  • The most common muscular dystrophy
 

Pathology

  • Mutation on the DMD gene, at Xp21.
  • There is a lack of the molecule dystrophin. This molecules is part of a complex structure that connects the cytoskeleton of each muscle fibre to the basal lamina. In the absence of dystrophin, there is excessive calcium entry into the cell. This results in excess oxidative stress within the cell, which damages the sarcolemma and ultimately results in cell death.
 

Clinical features

The condition is characterised by a progressive proximal muscle weakness and wasting. Typically diagnosed between age 5 and 5 ½ years.
Abnormal gait – particularly noticeable is difficulty on standing. There will often be an apparent Gower’s Sign 
  • Trouble getting up for chairs
  • Trouble getting upstairs
  • Clumsiness
  • Waddling gait
  • General difficulty with motor skills
  • Skeletal deformity
  • Most children unable to walk by age of 10 – and require the use of a wheelchair
  • Death usually occurs in the teenage years or early 20’s
    • Affected males do not normally survive to reproduce – so the disease is passed on almost entirely by female carriers.
  • Wasting of the proximal muscle (most obviously the thigh)
    • There may also be calf swelling due to pseudohypertrophy of the calf muscles. A similar process may also occur in the tongue. This is due to fat replacement of muscle.
  • Developmental delay in 1/3 of cases
 

Investigations

  • Positive Gower’s test
  • ↑Levels of creatinine kinase (CK) in the blood
  • EMG – shows destruction of muscle tissue, rather than nerve conduction properly
  • Genetic testing – will shows Xp21 defects
  • Muscle biopsy – rarely performed since genetic testing. Shows an absence of dystrophin.
 

Treatment

  • Corticosteroids – are aggressively used – sometimes before the age of 10. This can be extremely good treatment – it can convert from a Duchenne’s picture to a Becker’s picture.
  • Physiotherapy – can reduce the rate of contracture, and prolong the useful life of the muscles.
  • Mechanical ventilation - is often required in the late stages
 

Prognosis

  • In wheelchair usually about age of 10
  • Usually die by age of 20