Anorexia is associated with disorders of all systems.
Anorexia represents a consistent clinical manifestation during acute and chronic pathophysiological processes (
infection,
inflammation, injury, toxins, immunological reactions,
malignancy and
necrosis).
Anorexia during disease can be beneficial or deleterious depending on the timing and duration. Temporary
anorexia during
acute disease may be beneficial to an organism since a restriction in the intake of micro- and macro-nutrients will inhibit bacterial growth. Long-term
anorexia during
chronic disease, however, is deleterious to an organism and may be associated with
cachexia, which can ultimately result in death. Various mechanisms participate in the
anorexia observed during disease, including
cytokine action.
Anorexia induced by
cytokines is proposed to involve modulation of hypothalamic-feeding associated sites,
prostaglandin-dependent mechanisms, modifications of
neurotransmitter systems, gastrointestinal, metabolic, and endocrine factors. In addition, the
anorexia-
cachexia syndrome is multifactorial and may involve
chronic pain, depression or anxiety,
hypogeusia and
hyposmia, chronic
nausea, early satiety, malfunction of the gastrointestinal system, metabolic alterations,
cytokine action, production of other anorexigenic substances and/or iatrogenic causes (
chemotherapy,
radiotherapy).
Cachexia may result not only from
anorexia and a decreased caloric intake, but also from malabsorption and losses from the body (
ulcers,
hemorrhage, effusions), or a change in body metabolism. Research has focused on potential interventions to modify
anorexia during disease and the
anorexia-
cachexia syndrome. Nutritional modifications and the use of specific
steroids (such as
megestrol acetate) are being tested in the clinical setting. Understanding the specific mechanisms responsible for
anorexia during disease as well as their interactions is essential to develop interventions for the control of
anorexia (during a critical time in a specific disease), and to devise less toxic immunotherapeutic regimens using
cytokines.