Circadian Rhythm Sleep Disorders

Endogenous circadian rhythms in physiology and behavior are ubiquitous among mammals and are regulated by a master circadian clock, the suprachiasmatic nucleus of the hypothalamus. These intrinsic circadian rhythms are synchronized by light, melatonin, and social or physical activity to the 24-hour external light and dark cycles. Circadian rhythm sleep disorders (CRSD) occur when there is an alteration of the internal circadian timing mechanisms or a misalignment between the timing of sleep and the 24-hour social and physical environments. CRSDs, such as delayed sleep phase, advanced sleep phase and shift work sleep disorder, are often under-recognized, yet should be considered in the differential of patients presenting with symptoms of insomnia and/or hypersomnia. Because behavioral and environmental factors often are involved in the development and maintenance of these disorders, a multimodal treatment approach that combines behavioral and/or pharmacologic approaches is usually required. In addition to good sleep habits, timed exposure to bright light and melatonin can be used for the treatment of CRSD. Rapid advances in understanding the physiologic, cellular, and molecular basis of circadian rhythm and sleep regulation will likely lead to improved diagnostic tools and treatments for CRSDs.