Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a dystrophinopathy and the most common muscular dystrophy.

DMD has an incidence of 1 in 3500 to 5000 males 1,2. The condition is extremely rare in females due to its inheritance pattern, as discussed below 1.

The characteristic feature is progressive muscle weakness with fatty replacement of muscle that begins in early childhood 1,2. Typically, proximal lower limb and truncal muscles are affected first, but eventually there is progression to upper limb muscles and extremities 1,2.

In addition to gross motor weakness and delay, patients also exhibit muscle pseudohypertrophy especially of the calves, a waddling gait, scoliosis, joint contractures, and the classic yet non-specific Gower’s sign of proximal muscle weakness 1. Generally, children become wheelchair bound by approximately 12 years of age 1.

Furthermore, patients have many other non-musculoskeletal features:

  • dilated cardiomyopathy characterised by fibrosis of the posterobasal left ventricular wall and leading to congestive heart failure 1,3
  • cardiac conduction anomalies leading to a variety of potential arrhythmias 1,3
  • restrictive lung disease 1
  • intellectual disability 1

DMD is inherited in an X-linked recessive pattern, and thus nearly exclusively occurs in males 1. It is due to a mutation in the DMD gene that normally encodes for dystrophin, a protein involved in strengthening skeletal and cardiac muscle fibres by acting as a mechanical link between the cytoskeleton and the extracellular glycoprotein matrix of cells in these tissues 1.

Unlike in Becker muscular dystrophy where a mutation in the DMD gene results in a partially functioning dystrophin protein, in Duchenne muscular dystrophy dystrophin is non-functioning, which results in a more severe phenotype 1.

Musculoskeletal MR features, especially those from the lower limb, are most commonly described, however other imaging modalities may be useful as well.

Plain radiograph may show non-specific features of DMD, such as translucent soft tissues reflective of fatty muscle replacement, scoliosis, hypo-inflated lungs, and gracile bones 4,5.

CT is not commonly performed due to risks of ionising radiation in this young patient demographic 2,6. However, CT confirms plain radiograph findings and furthermore, typically shows low attenuating fatty infiltration and resultant pseudohypertrophy of affected muscles (see below) 6.

MRI is the modality of choice in DMD, with T1-weighted sequences traditionally being the most useful 7. Due to its superior soft tissue contrast, T1-weighted MRI shows characteristic patterns of muscular fatty infiltration 7. Affected muscles demonstrate high T1-weighted signal that is initially streaky, but becomes more confluent in nature as the condition progresses 7.

There tends to be a typical pattern of muscle involvement:

Furthermore, recent research suggests T2 mapping techniques may also be useful applications of MR, especially in relation to clinicoradiological severity correlations, but this is an ongoing field of research 2,9.

Corticosteroids, such as prednisolone and deflazacort, are the only pharmacological agent that has proven to be effective in improving muscle strength and respiratory function 1. Otherwise, the management of DMD is multidisciplinary, and involves rehabilitation and surveillance of respiratory, cardiac, and orthopaedic complications 1.

The prognosis remains relatively poor, with most patients not surviving past the third decade of life 1.

This disorder is named after Guillaume-Benjamin-Amand Duchenne de Boulogne (1806-1875), a French neurologist, who first described the condition in his 1861 book 10,11.

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Article information

rID: 55043
Tag: cases
Synonyms or Alternate Spellings:
  • Duchenne's muscular dystrophy
  • Duchenne muscular dystrophy (DMD)
  • Duchenne's muscular dystrophy (DMD)

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