Atrophy is a medical term that refers to a decrease in size of an organ or part of the body. Atrophy may result from disuse; for example, long-term immobility of a leg due to paralysis may lead to atrophy of the leg muscles. Atrophy may also result from cell death, loss of blood supply, malnutrition, or hormonal changes. For example, Alzheimer's disease causes progressive atrophy to the brain as brain cells (neurons) die during the course of the disease.