title: Correlates and prognostic relevance of sleep irregularity in inter-episode bipolar disorder.
abstract: OBJECTIVE
  Sleep-wake disturbances, such as sleep irregularity, are common in bipolar disorder. Early studies suggest that sleep irregularity is associated with mood symptoms in bipolar disorder, but little research has been conducted to identify other correlates of sleep irregularity. We investigated the relationship between sleep irregularity and sleep quality, social rhythms, eveningness, sleep-related cognitions and behaviors, and past and future mood episodes in 84 patients with inter-episode bipolar I or II disorder.
  
  
  METHODS
  This is a retrospective and prospective, naturalistic follow-up study. The Expanded Consensus Sleep Diary, Pittsburgh Sleep Quality Index (PSQI), Social Rhythm Metric (SRM-II-5), Composite Scale of Morningness (CSM), Dysfunctional Beliefs and Attitudes About Sleep Scale (DBAS-16), and Sleep Hygiene Practice Scale (SHPS) were administered. The Square Successive Difference (SSD), derived from a week-long sleep diary, was used as an index of sleep irregularity. Multilevel modeling analysis, which adjusts for biases in parameter estimates, was used to minimize the impact of missing data. Bonferroni correction was performed to account for multiple testing.
  
  
  RESULTS
  Higher SSD scores of sleep diary variables were significantly associated with higher PSQI, SRM-II-5, DBAS-16, and SHPS scores. Irregularity in total sleep time was related to more depressive episodes in the past 5years (p=.002), while irregularity in wake after sleep onset predicted the onset of depressive episodes over the next 2years (p=.002).
  
  
  CONCLUSIONS
  Sleep irregularity was associated with poor sleep quality, irregular social rhythms, dysfunctional sleep-related cognitions and behaviors, and greater number of depressive episodes in bipolar disorder.
authors.affiliation: Department of Psychology, Temple University, Philadelphia, PA, United States.
authors.forename: Tommy H
authors.initials: TH
authors.lastname: Ng
authors.affiliation: Department of Psychiatry, University of Hong Kong, Hong Kong, SAR, China. Electronic address: kfchung@hkucc.hku.hk.
authors.forename: Ka-Fai
authors.initials: KF
authors.lastname: Chung
authors.affiliation: Department of Applied Social Sciences, City University of Hong Kong, Hong Kong, SAR, China.
authors.forename: Ting-Kin
authors.initials: TK
authors.lastname: Ng
authors.affiliation: Department of Psychiatry, Queen Mary Hospital, Hong Kong, SAR, China.
authors.forename: Chit-Tat
authors.initials: CT
authors.lastname: Lee
authors.affiliation: Department of Psychiatry, Queen Mary Hospital, Hong Kong, SAR, China.
authors.forename: Man-Sum
authors.initials: MS
authors.lastname: Chan
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001714:Bipolar Disorder / Q000175:diagnosis* / Q000523:psychology*; D005260:Female; D005500:Follow-Up Studies; D006723:Hong Kong; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D011446:Prospective Studies; D012189:Retrospective Studies; D012892:Sleep Deprivation / Q000175:diagnosis / Q000523:psychology; D012893:Sleep Wake Disorders / Q000175:diagnosis* / Q000523:psychology*; D055815:Young Adult