Skeletal muscle serves as a storage site for amino acids that can be used for energy production when demands are high or supplies are low. If metabolic demands remain greater than protein synthesis, muscle mass is lost. Many diseases and conditions can lead to this imbalance, either through the disease itself or disease associated appetite-changes. Causes of<unk> , include immobility, aging, malnutrition, certain systemic diseases (cancer, congestive heart failure; chronic obstructive pulmonary disease; AIDS, liver disease, etc.), deinnervation, intrinsic muscle disease or medications (such as glucocorticoids). Immobility Disuse is a common cause of<unk>  and can be local (due to injury or casting) or general (bed-rest). The rate of<unk>  from disuse (10-42 days) is approximately 0.5–0.6% of total muscle mass per day although there is considerable variation between people. The elderly are the most vulnerable to dramatic muscle loss with immobility. Much of the established research has investigated prolonged disuse (>10 days), in which the muscle is compromised primarily by declines in muscle protein synthesis rates rather than changes in muscle protein breakdown. There is evidence to suggest that there may be more active protein breakdown during short term immobility (<10 days). Cachexia Certain diseases can cause a complex muscle wasting syndrome known as cachexia. It is commonly seen in cancer, congestive heart failure, chronic obstructive pulmonary disease, chronic kidney disease and AIDS although it is associated with many disease processes, usually with a significant inflammatory component. Cachexia causes ongoing muscle loss that is not entirely reversed with nutritional therapy. The pathophysiology is incompletely understood but inflammatory cytokines are considered to play a central role. In contrast to weight loss from inadequate caloric intake, cachexia causes predominantly muscle loss instead of fat loss and it is not as responsive to nutritional intervention. Cachexia can significantly compromise quality of life and functional status and is associated with poor outcomes. Sarcopenia Sarcopenia is the degenerative loss of skeletal muscle mass, quality, and strength associated with aging. This involves<unk> , reduction in number of muscle fibers and a shift towards "slow twitch" or type I skeletal muscle fibers over "fast twitch" or type II fibers. The rate of muscle loss is dependent on exercise level, co-morbidities, nutrition and other factors. There are many proposed mechanisms of sarcopenia and is considered to be the result of changes in muscle synthesis signalling pathways and gradual failure in the satellite cells which help to regenerate skeletal muscle fibers, but is incompletely understood. Sarcopenia can lead to reduction in functional status and cause significant disability but is a distinct condition from cachexia although they may co-exist. In 2016 an ICD code for sarcopenia was released, contributing to its acceptance as a disease entity. Intrinsic muscle diseases Muscle diseases, such as muscular dystrophy, amyotrophic lateral sclerosis (ALS), or myositis such as inclusion body myositis can cause<unk> . Central nervous system damage Damage to neurons in the brain or spinal cord can cause prominent<unk> . This can be localized<unk>  and weakness or paralysis such as in stroke or spinal cord injury. More widespread damage such as in traumatic brain injury or cerebral palsy can cause generalized<unk> . Peripheral nervous system damage Injuries or diseases of peripheral nerves supplying specific muscles can also cause<unk> . This is seen in nerve injury due to trauma or surgical complication, nerve entrapment, or inherited diseases such as Charcot-Marie-Tooth disease. Medications Some medications are known to cause<unk> , usually due to direct effect on muscles. This includes glucocorticoids causing glucocorticoid myopathy or medications toxic to muscle such as doxorubicin. Endocrinopathies Disorders of the endocrine system such as Cushing's disease or hypothyroidism are known to cause<unk> .
Muscle atrophy
Muscle weakness
Muscle hypertrophy
Breast atrophy
Muscle imbalance
Lipoatrophy
Tooth loss
Lumbar enlargement