Duchenne muscular dystrophy is usually recognized by the third year of life and almost always before the sixth year. Nearly half of children show evidence of disease before beginning to walk. Many of them are slightly backward in other ways (mild developmental delay) and the muscle weakness may at first be overlooked. A greatly elevated CK may be the clue. In another group of young children, an indisposition to walk or run normally at the expected time brings them to medical attention or, having achieved these motor milestones, they appear less active than expected and are prone to falls. Increasing difficulty in walking, running, and climbing stairs, excessive lumbar lordosis, and waddling gait become more obvious as time passes. The iliopsoas, quadriceps, and gluteal muscles are involved initially; then the pretibial muscles weaken (foot-drop and toe walking). Muscles of the pectoral girdle and upper limbs are affected after the pelvicrural ones; the serrati, lower parts of pectorals, latissimus dorsi, biceps, and brachioradialis muscles are affected, more or less in this order.
Enlargement of the calves and certain other muscles is progressive in the early stages of the disease but most of the muscles, even the ones that are originally enlarged, eventually decrease in size; only the gastrocnemii, and to a lesser extent the lateral vasti and deltoids, are consistently large and this peculiarity may attract attention before the weakness becomes evident. The enlarged muscles have a firm, resilient (“rubbery”) feel and are slightly weaker and more hypotonic than healthy ones. Thus the muscle enlargement is a pseudohypertrophy. Rarely, all muscles are at first large and strong, even the facial muscles, as in one of Duchenne’s cases (from the marble statue, Farnese Hercules); histologically, this is a true muscle hypertrophy.
Muscles of the pelvic girdle, lumbosacral spine, and shoulders become weak and wasted, accounting for certain clinical peculiarities. Weakness of abdominal and paravertebral muscles accounts for a lordotic posture and protuberant abdomen when standing and the rounded back when sitting. Weakness of the extensors of the knees and hips interferes with equilibrium and with activities such as climbing stairs or rising from a chair or from a stooped posture. In standing and walking, the patient places his feet wide apart so as to increase his base of support. To rise from a sitting position, he first flexes his trunk at the hips, puts his hands on his knees, and pushes the trunk upward by working the hands up the thighs. In rising from the ground, the child first assumes a four-point position by extending the arms and legs to the fullest possible extent and then works each hand alternately up the corresponding thigh (the sign traditionally attached to Gowers’ name). In getting up from a recumbent position, the patient turns his head and trunk and pushes himself sideways to a sitting position. S.A.K. Wilson used an alliterative phrase to describe the characteristic abnormalities of stance and gait: The patient “straddles as he stands and waddles as he walks.” The waddle is the result of bilateral weakness of the gluteus medius. Many affected boys have a tendency to walk on their toes as a consequence of contractures in the gastrocnemii muscles. Calf pain is frequent. Weakening of the muscles that fix the scapulae to the thorax (serratus anterior, lower trapezius, rhomboids) causes winging of the scapulae, and the scapular angles can sometimes be seen above the shoulders when one is facing the patient.