A 4-year-old boy is brought to the physician by his parents because he tires easily. Physical examination reveals weakness in the pelvic and shoulder girdles and enlargement of the child's calf muscle. Serum levels of creatine kinase are elevated. A biopsy of calf muscle shows marked variation in size and shape of muscle fibers. There are foci of muscle fiber necrosis, with myophagocytosis, regenerating fibers, and fibrosis. What will be the likely cause of death in the patient?

The symptoms of Duchenne muscular dystrophy (DMD) progress with age. During the first year of life, the infants appear normal, but more than half fail to walk by 18 months of age. More than 90% of afflicted boys are wheelchair bound by the age of 11 years. In advanced disease, cardiac symptoms are almost universal, and cardiomyopathy is a common cause of death. The mean age at death in boys with DMD is 17 years. The other choices are unrelated to DMD.Diagnosis: Duchenne muscular dystrophy