title: Circadian Rhythm Sleep Disorders.
abstract: OBJECTIVE
  To review circadian rhythm sleep disorders, including underlying causes, diagnostic considerations, and typical treatments.
  
  
  METHODS
  Literature review and discussion of specific cases.
  
  
  RESULTS
  Survey studies1,2suggest that up to 3% of the adult population suffers from a circadian rhythm sleep disorder (CRSD). However, these sleep disorders are often confused with insomnia, and an estimated 10% of adult and 16% of adolescent sleep disorders patients may have a CRSD3-6. While some CRSD (such as jet lag) can be self-limiting, others when untreated can lead to adverse medical, psychological, and social consequences. The International Classification of Sleep Disorders classifies CRSD as dyssomnias, with six subtypes: Advanced Sleep Phase Type, Delayed Sleep Phase Type, Irregular Sleep Wake Type, Free Running Type, Jet Lag Type, and Shift Work Type. The primary clinical characteristic of all CRSD is an inability to fall asleep and wake at the desired time. It is believed that CRSD arise from a problem with the internal biological clock (circadian timing system) and/or misalignment between the circadian timing system and the external 24-hour environment. This misalignment can be the result of biological and/or behavioral factors. CRSD can be confused with other sleep or medical disorders.
  
  
  CONCLUSIONS
  Circadian rhythm sleep disorders are a distinct class of sleep disorders characterized by a mismatch between the desired timing of sleep and the ability to fall asleep and remain asleep. If untreated, CRSD can lead to insomnia and excessive daytime sleepiness, with negative medical, psychological, and social consequences. It is important for physicians to recognize potential circadian rhythm sleep disorders so that appropriate diagnosis, treatment, and referral can be made.
authors.affiliation: Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital and Division of Sleep Medicine, Harvard Medical School, Boston, MA USA ; Department of Neurology, Howard OsanDongtan Hospital, Osan, Korea.
authors.forename: Min Ju
authors.initials: MJ
authors.lastname: Kim
authors.affiliation: Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital and Division of Sleep Medicine, Harvard Medical School, Boston, MA USA ; Department of Psychiatry, Kangwon National University Hospital, Chunchon, South Korea.
authors.forename: Jung Hie
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital and Division of Sleep Medicine, Harvard Medical School, Boston, MA USA.
authors.forename: Jeanne F
authors.initials: JF
authors.lastname: Duffy