Delayed sleep-wake phase disorder

Delayed sleep-wake phase disorder (DSWPD) (1) is thought to be the most common of the circadian rhythm sleep-wake disorders (CRSDs); an increasingly recognized and diagnosed group of sleep disorders in which the main problem is inappropriate timing of the major sleep episode relative to the light-dark cycle. Their names are self-explanatory, and as well as DSWPD include Advanced Sleep Wake Phase Disorder, in which the major sleep episode occurs every 24 h, but inappropriately early relative to darkness; the non-24 h Sleep-Wake Phase Disorder, in which the major sleep episode is desynchronised from the light-dark cycle, and assumes its own period of greater than 24 h; and irregular sleep-wake disorder, where there is no temporal pattern to the major sleep episode. These disorders may be considered ‘intrinsic’, and are often chronic, and caused by a variety of factors. On the other hand, ‘extrinsic’ CRSDs also occur, and are caused by imposition of a different light-dark cycle (as in Jet Lag Disorder) or routine (Shift-Work Disorder)