Distinguishing muscular dystrophy from central causes of motor delay

What it is

A child brought to a well child check who is walking only with assistance raises the question of gross motor delay. Some abnormal gross motor developmental findings suggest muscular dystrophy; others suggest a central cause of motor delay such as cerebral palsy. Telling those two apart is the whole task.

How it presents

Duchenne muscular dystrophy is an X-linked recessive disorder of the dystrophin gene. Progressive muscle paresis and atrophy start in the proximal lower limbs (pelvic girdle) and extend to the upper body and distal limbs as the disease progresses. Difficulty walking comes from that pelvic girdle weakness, and it shows as weak reflexes, waddling gait, the Gower maneuver, calf pseudohypertrophy and frequent falls due to poor balance. Progression is rapid, with inability to walk by approx. 12 years. Lumbar lordosis and scoliosis follow, along with cognitive impairment.

Cardiac and respiratory muscle involvement is part of the disease: dilated cardiomyopathy is a common cause of death, and arrhythmias and respiratory insufficiency belong to the same picture.