Circadian rhythm disorders.

Circadian rhythm sleep disorders occur when individuals attempt to sleep at the wrong circadian time. The misalignment between the internal circadian timing system and the external environment is typically due to either an alteration in the functioning of the circadian timing system (e.g., delayed or advanced sleep phase syndrome) or to changes in the external environment (e.g., jet lag). However, the clinical presentation of most of the circadian rhythm sleep disorders is influenced by a combination of physiological, behavioral, and environmental factors. These disorders lead to complaints of insomnia and excessive daytime sleepiness, with impairment in important areas of functioning and quality of life. Current treatments primarily involve the use of circadian synchronizing agents, such as light, to realign the internal and external environment. These treatments are limited by the availability of adequate diagnostic tools and well-controlled clinical trials. A better understanding of the pathophysiology of these disorders is required to develop more effective treatments.