Duchenne and Becker muscular dystrophy: Case

This boy has the classic presentation of Duchenne muscular dystrophy. The delayed walking, the toe-walking gait with lumbar lordosis, the firm calf pseudohypertrophy, the Gowers sign, the proximal weakness worse in the legs, and the reduced reflexes together form a recognisable picture, and the creatine kinase of 31,000 units per litre settles the direction of the workup. The high alanine aminotransferase with a normal bilirubin is muscle-derived, because the same enzymes leak from the damaged fibre, so this is not a liver problem. ^[3]

Clinical findings and assessment

The key findings are the proximal weakness worse in the legs, the calf pseudohypertrophy, the Gowers sign, the reduced reflexes, and the creatine kinase of 31,000. The weakness is proximal and symmetrical, the pelvic girdle failing before the shoulder girdle, and the face and the eyes are spared, which separates a primary muscle disease from a more generalised neurological process. The firm calves are the pseudohypertrophy of fat and fibrosis that replace the necrotic fibre, and the reduced reflexes reflect the loss of the muscle. The creatine kinase, between 10,000 and 100,000, is off the scale and points to a dystrophic process. ^[4]

The timed function tests grade and track the disease. The time to stand from the floor, the ten-metre run, the climb of four stairs, and the six-minute walk are measured, because the trend over time reveals the motor plateau that should trigger the glucocorticoid decision and the decline that heralds the loss of ambulation. The joints are checked for the contractures of the Achilles, the hamstrings, and the iliotibial bands, the spine for the scoliosis that will come once he is in a wheelchair, and the heart for the gallop of the early cardiomyopathy. ^[4]