History and exam

Key diagnostic factors

common

presence of risk factors

A positive family history of DMD and male sex are risk factors strongly associated with DMD.

imbalance of lower limb strength

Hip and knee flexors and ankle plantar flexors are stronger than hip and knee extensors and ankle dorsiflexors in patients with DMD.

lower extremity musculotendinous contractures

The first contractures seen in patients with DMD are increased lumbar lordosis and heel cord contractures. These are caused by imbalance of lower body strength.

Because the hip extensors are weaker than the hip flexors, the patient must keep the centre of gravity behind the hip to avoid jack-knifing. Likewise, jack-knifing occurs at the knees if the centre of gravity is behind the knees, because the knee extensors are weaker than the hamstrings. Thus, the patient tends to walk with increased lordosis and on the toes to keep the centre of gravity behind the hips and in front of the knees.[Figure caption and citation for the preceding image starts]: 7-year-old boy with Duchenne muscular dystrophy standing, maintaining centre of gravity behind the hips and anterior to the kneesFrom the collection of John R. Bach, MD, FAAPMR; used with permission [Citation ends].com.bmj.content.model.Caption@685b1f05

delayed motor milestones

Ambulation is usually mildly delayed, with independent ambulation often not being attained by 18 months.[10]​[22]​

calf hypertrophy

Common in DMD, due to the ongoing regeneration of muscle fibres characteristic of all muscular dystrophies.[22][23]​

ambulation difficulty and falls

Untreated patients with DMD are rarely able to run or jump. Ambulation difficulty and falls may also be an initial observation for children whose diagnosis has been delayed.[22][23]

diminished muscle tone and deep tendon reflexes

Diminished in all muscle groups in DMD.

If tone and reflexes are increased, an alternative diagnosis needs to be considered.

normal sensation

All modalities of sensation are intact in DMD.

If sensation is abnormal, an alternative diagnosis needs to be considered.

Gowers' sign

The relatively weaker hip extensors, knee extensors, and ankle dorsiflexors result in the patient 'climbing up his body' to come to stand from a seated position. This is characteristic of children with DMD from ages 4 to 7 years.[10]​[22]​[23]​

Children with DMD have an imbalance of strength at all lower extremity pivots.

Other diagnostic factors

common

toe walking

Due to low muscle tone.[10][22] Children with DMD tend to be symmetrically affected.

The great majority of children who walk on their toes have static encephalopathies (not muscular dystrophies) and at least mild spasticity. In many of these cases the children are asymmetrically affected.

hypotonia

At birth, infants with DMD are often described as mildly floppy and are subsequently hypotonic.

hyperactivity

Some patients with DMD are hyperactive and have difficulty in focusing attention.[23]​

urinary and bowel incontinence

Consistent with DMD.

mild to severe intellectual disability

Mild to severe intellectual disability is consistent with DMD, but is not always associated with the condition.[10]​[22]​[23]​

Risk factors

strong

family history

The mother or siblings may be known carriers, or there may be siblings with the disease.

Two-thirds of cases of DMD are inherited from a mother carrying a genetic mutation on the X chromosome at the Xp21 position. One third of cases result from spontaneous mutations.[11]​

Other muscular dystrophies and spinal muscular atrophy are also predominantly inherited conditions.

male sex

Because inheritance of DMD and Becker muscular dystrophy is X-linked, the overwhelming majority of patients are male.

Female carriers of DMD or Becker muscular dystrophy typically have few or no symptoms or signs, but some may be detected after an incidental finding of elevated serum creatine kinase.

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