25. Duchenne’s Dystrophy
Definition
Duchenne’s dystrophy is a chronic, progressive, severe pseudohypertrophic muscular dystrophy—the most commonly occurring type. It is characterized by increasing weakness of pelvic and shoulder girdle musculature, pseudohypertrophy of the muscles, then atrophy and lordosis. People with the disease have a peculiar, particular swinging gait (waddling gait) with the legs kept wide apart.
Diagnostic Criteria for Duchenne’s Dystrophy
• Absence of bowel or bladder dysfunction
• Hyperlordosis with wide-based gait
• Hypertrophy of weak muscles
• Progressive course over time
• Reduced muscle contractility and electrical stimulation in advanced disease
• Sensory distribution or febrile illness
• Weakness, with onset in the legs
Signs and Symptoms of Rhabdomyolysis
• Hyperphosphatemia
• Hyperuricemia
• Lactic acidosis
• Loss of P wave or sine wave
• Peaked T waves
• Prolonged P-R and QRS intervals
• Rising creatinine phosphokinase levels
• Severe hyperkalemia
• Tea-colored urine
Incidence
This form of muscular dystrophy occurs at the rate of 1:3300 to 1:3500 births, and affects males much more often than females.
Etiology
Duchene’s dystrophy is the result of a sex-linked, recessive inheritance. A mutation in the dystrophin gene is found on the X-chromosome at the Xp21 stripe. The resultant loss of dystrophin is the first step in an interdependent series of events that includes the loss of other portions of the dystrophin-associated glycoprotein complex, breakdown of the sarcolemma with influx of calcium ions, phospholipase activation, and oxidative cellular injury. The process culminates in myonecrosis. With progression of the myonecrosis, and thus the disease, dead muscle fibers are removed by macrophages. The subsequent void is filled by both fatty and connective tissue to such an extent that the muscle appears to grow and is deceptively healthy in outward appearance, which accounts for the pseudohypertrophy.
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