Dystrophinopathies: Duchenne Muscular Dystrophy—Gower’s Maneuver


Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy (incidence is 1 in 3917 live male births [Norway] to 1 in 4700 [Nova Scotia]). Becker muscular dystrophy (BMD) has a relatively milder clinical course (incidence from about 1 in 18,000 to 1 in 31,000 male births). Both DMD and BMD are inherited as X-linked recessive traits and present similarly. A third allelic type of muscular dystrophy, of intermediate severity, is recognized in patients known as “outliers.” All three types result from dystrophin deficiency caused by mutations of the DMD gene.


Other dystrophinopathies occur at significantly lower incidences. These include carrier females who manifest DMD/BMD, DMD-associated dilated cardiomyopathy (DCM), and muscle cramps with myoglobinuria.


CLINICAL ASPECTS


The clinical features and course of the various dystrophinopathies vary across a wide spectrum. DMD, BMD, and the “outliers” (intermediate phenotype) have the most severe skeletal muscle involvement, and DCM has the most severe heart muscle involvement. DMD/BMD carrier females may be asymptomatic or manifest mild-to-severe symptoms. The age of wheelchair confinement distinguishes DMD and BMD clinically and is less than 13 years in DMD, more than 16 years in BMD, and between 13 and 16 years in outliers.


DUCHENNE MUSCULAR DYSTROPHY


The onset of weakness in children with DMD usually occurs between 2 and 3 years of age and nearly always before age 5 years. Clinical signs include difficulty with running, jumping, going up steps, and other similar activities; an unusual waddling gait; lumbar lordosis; and calf enlargement. Symmetric muscular weakness affects proximal before distal limb muscles and the lower before upper extremities. Affected boys may complain of leg pains and display Gower’s sign (using hand support to push themselves from the floor to an upright position). Neck flexor weakness distinguishes boys with DMD from those with milder presentations. Cardiac muscle is also affected. Cognitive function may rarely be average or above average but is usually impaired to a varying degree. Physical examination shows pseudohypertrophy of the calf muscles; possible pseudohypertrophy of quadriceps, gluteal, deltoid, and other muscles; lumbar lordosis; waddling gait; shortening of the Achilles tendons, leading to toe walking; and hyporeflexia or areflexia.


Although transient clinical improvement may be seen between 3 and 6 years of age, because normal maturation initially exceeds the early dystrophic process, relentless deterioration gradually follows, leading to wheelchair confinement. Contractures, scoliosis, and deterioration of pulmonary function follow wheelchair confinement. Cardiomyopathy affects about one third of patients by age 14 years, one half by age 18 years, and all patients after age 18 years. Intestinal hypomotility, also known as intestinal pseudo-obstruction, can be a life-threatening complication in patients with DMD. Cause of death is usually respiratory insufficiency or cardiac failure; most patients with DMD die in their late teens or twenties. Assisted ventilation can prolong a patient’s life expectancy but does not improve the patient’s ability to perform activities of daily living.


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Sep 2, 2016 | Posted by in NEUROLOGY | Comments Off on Dystrophinopathies: Duchenne Muscular Dystrophy—Gower’s Maneuver

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