Fatigue and Sleepiness in Circadian Rhythm Sleep Disorders

Abstract

Excessive sleepiness is a defining characteristic of circadian rhythm sleep disorders (CRSDs) and is often the presenting complaint of individuals who are eventually diagnosed with such a disorder. Such sleepiness results primarily from a misalignment between the external environment and the propensity for sleep, but may also be exacerbated by chronically disrupted sleep and accumulating sleep debt. In the extrinsic types of CRSDs – shift work sleep disorder and jet lag sleep disorder – the reasons for excessive sleepiness are quite obvious, and both the sleepiness and treatment thereof have been relatively well investigated. For the intrinsic types of CRSDs – particularly, delayed sleep phase disorder (DSPD) and advanced sleep phase disorder (ASPD) – sleepiness levels, timing, and treatment have not been as well characterized. Indeed, it is unknown whether those with ASPD and DSPD are sleepier than normal at times other than would be expected given the altered sleep timing in these disorders (i.e., evening hours in ASPD and morning hours in DSPD). Treatment approaches for excessive sleepiness in CRSDs are generally secondary to direct treatment of the circadian misalignment at the root of such sleepiness, although wakefulness-promoting agents have also been used effectively, particularly in those with shift work sleep disorder.