What are the initial signs and symptoms of Duchenne muscular dystrophy (DMD)?

Updated: Aug 17, 2020
  • Author: Twee T Do, MD; Chief Editor: Jeffrey D Thomson, MD  more...
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Answer

The child's motor milestones may be at the upper limits of normal, or they may be slightly delayed. Some of the delays may be caused by inherent muscle weakness, but a component may stem from brain involvement.

Although the association of intellectual impairment in MD has long been recognized, it was initially thought to be a result of limited educational opportunities. [19] Psychometric studies have since revealed a definitively lower intelligence quotient (IQ) in patients with Duchenne MD despite equalization of educational opportunities. [20] The average IQ in patients with Duchenne MD is 85 points on the Wechsler Adult Intelligence Scale (WAIS), compared with 105 points in healthy populations. [13, 19, 20, 21]

In addition to mental deficits, another milestone delay is the patient's age at ambulation. Children with Duchenne MD usually do not begin to walk until about age 18 months or later. In the Dubowitz study, [13] 74% of children with Duchenne MD manifested the disease by age 4 years. By age 5 years, awareness increases as the disease is manifested in all affected children when they experience difficulty with school-related activities (eg, getting to the bus, climbing stairs, reciprocal motions during activities).

Other early features include a gait abnormality, which classically is a waddling, wide-based gait with hyperlordosis of the lumbar spine and toe walking. The waddle is due to weakness in the gluteus maximus and gluteus medius muscles and the patient's inability to support a single-leg stance. The child leans the body toward the other side to balance the center of gravity, and the motion is repeated with each step.

Hip extensor weakness also results in a forward tilt of the pelvis, which translates to a hyperlordosis of the spine to maintain posture. The child then walks on tiptoes because it is easier to stay vertical with an equinus foot position than on a flat foot, though no real tendo Achillis contracture exists at this early point.

Gradually, the child is observed to have increasingly noticeable difficulty with step taking. Frequent falls without tripping or stumbling often occur and are described as the feet being swept away from under the child. The child then begins having problems getting up from the sitting or supine position, and he or she can rise to an upright stance only by manifesting the Gower sign.


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