Progressive and symmetrical wasting of muscles of
the legs and pelvis and later of the thorax and upper limbs. Muscle weakness
appears insidiously between 2 and 5 years of age, producing a waddling gait
and lordosis. Soon thereafter, the calf muscles become enlarged
(pseudohypertrophy). These boys have difficulty standing up (Gowers sign)
and climbing stairs, develop contractures, and become wheelchair-bound by
age 10 to 12 years (sometimes earlier). Joint deformities, muscle
retractions, and degenerations are common. Collapse of the spine results in
severe scoliosis and restrictive pulmonary disease. Often these patients are
obese (secondary to lack of physical activity and fatty degeneration of the
muscles), show mild mental retardation (with an average IQ in the mid-80s),
and hypertrophy of the tongue. Clinically apparent dilated cardiomyopathy
(which initially may have been hypertrophic), often with persistent sinus
tachycardia and conduction system abnormalities (ECG changes, most often
consisting of signs of right ventricular hypertrophy and/or right bundle
branch block, occur in 40-90% of patients), is a common feature in
adolescents with DMD. Occasionally, left-sided endocardial thickening (left
atrial and left ventricular) occurs. Echocardiography may reveal normal
systolic but pathologic diastolic left ventricular function (i.e., decreased
diastolic relaxation). Mitral valve prolapse has been reported in about one
fourth of patients and may be secondary to fatty degeneration of the
papillary muscles. Weakness of the diaphragm is an ominous sign that usually
occurs in the second decade of life and may result in hypoventilation and
hypoxia. Death most often occurs late in the second decade from respiratory
complications (>90%) and/or cardiac complications (10%).