Becker Muscular Dystrophy Clinical Presentation

Updated: Aug 08, 2017
  • Author: Benjamin R Mandac, MD; Chief Editor: Stephen Kishner, MD, MHA  more...
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Presentation

History

A typical developmental history of a patient with BMD may include the following:

  • Delayed gross motor milestones (eg, late walking, running, jumping, difficulty with stair climbing) may be reported.

  • Initially, some children who are later diagnosed with BMD may be called clumsy.

  • Increasing numbers of falls, toe walking, and difficulty rising from the floor may be later features.

  • Proximal muscle weakness is reported.

  • Subclinical cases may manifest later in life; dilated cardiomyopathy can be the first sign of BMD.

  • Elbow contractures may be seen later in life.

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Physical

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  • The Gower sign is not a specific finding for muscular dystrophy, but it does point to proximal weakness in the hip extensors, leading to the pattern of movement seen when patients rise from the floor.

  • A weakness pattern limited to specific muscle groups may help to differentiate BMD from other muscular dystrophies (such as limb-girdle and Emery-Dreifuss muscular dystrophies).

  • Progressive, symmetrical muscle weakness and atrophy with pseudohypertrophic calves may be seen.

  • Cases have been described of patients presenting without weakness but with symptoms of cardiomyopathy or cramps as the only indication of a myopathic process. Isolated weakness to the quadriceps femoris may be the only symptom noted.

  • Fasciculation or sensory modality abnormalities can exclude the diagnosis of a dystrophinopathy.

  • Preservation of neck flexor muscle strength may differentiate BMD from DMD.

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Causes

BMD is an X-linked, recessive, inherited disorder. A family history of similarly affected maternal uncles assists the clinician in confirming a diagnosis of BMD.

  • A woman is an obligate heterozygote if she has an affected son and one other affected relative in the maternal line.

  • A woman with more than 1 affected child and no family history in the maternal line may have a germline mutation or a germline mosaicism.

  • An isolated proband without a family history may be explained by a mutation occurring in the egg at or following conception in which only some cells were affected (mosaicism). On the other hand, the proband's mother may have inherited the gene mutation if (1) her mother was a carrier or (2) her mother or father had somatic or germline mosaicism.

  • Siblings of the proband are at risk of transmitting the gene defect based on the carrier status of the mother.

    • A carrier mother has a 50% transmission rate for the mutation, per pregnancy; daughters inheriting the mutation will be carriers, and sons with the mutation will be affected.

    • Mothers with germline and/or somatic mosaicism have a higher risk of transmitting the mutation.

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