atrophy

Atrophy is a reduction in the size of an organ or tissue, resulting from a decrease in cell size (atrophy of cells) and/or loss of cells. It is a common response to reduced functional demand, decreased blood supply, aging, or endocrine and nutritional changes. Atrophy is distinct from hypoplasia (underdevelopment) and from necrosis (cell death).

Cellular mechanisms involve decreased protein synthesis and increased protein degradation, often mediated by the ubiquitin-proteasome system and autophagy-lysosome pathways. Mitochondrial dysfunction and reduced cellular metabolism can contribute. The process can be reversible if the underlying cause is removed, especially in early stages; chronic atrophy can become fibrotic and less reversible.

Causes include disuse atrophy from immobilization or sedentary life; denervation atrophy after nerve injury; ischemic atrophy from reduced blood flow; endocrine or nutritional-related atrophy such as cachexia, malnutrition, or hormonal deficiencies; and age-related sarcopenia. Atrophy can affect muscles, brain, kidneys, heart, and other organs.

Examples: Skeletal muscles after limb immobilization show decreased cross-sectional area; brain atrophy occurs in aging and neurodegenerative diseases; testicular or ovarian atrophy can follow hypogonadism or malnutrition; retinal or optic nerve atrophy can result from disease or injury.

Diagnosis is usually based on imaging or histology showing reduced organ or tissue size with preserved architecture of some parts, and clinical history to identify the cause. Management targets the underlying cause and may include physical therapy, nutrition, and treatment of neurological or vascular issues. The prognosis depends on tissue type, duration, and ability to reverse the contributing factor.