title: Seasonal variation of mixed and pure episodes of bipolar disorder.
abstract: BACKGROUND
  Although seasonal patterns of manic episodes have been reported, the seasonal variation of mixed states of bipolar disorder has received little attention. In the current report we address that concern as well as the overall seasonality of manic episodes.
  
  
  METHODS
  The seasonal pattern of 304 psychiatric hospital admissions for treatment of mixed or manic bipolar episodes over a 3-year period were analyzed employing two definitions of mixed manic states: DSM-III-R and an ROC derived definition.
  
  
  RESULTS
  The frequency of all manic episodes combined peaked in early spring, with a nadir in late fall. Pure manic admissions showed a similar pattern. Mixed manic admissions had a significantly different pattern, with a peak in late summer and a nadir in November. The differences between pure and mixed manic admissions were demonstrated with the use of the ROC definition for mixed states.
  
  
  CONCLUSIONS
  Effects of medications and medication non-compliance may dampen natural seasonal patterns of episodes.
  
  
  CONCLUSIONS
  The different seasonal pattern of mixed and pure manic episodes support the separation of mixed episodes as a distinct clinical subtype.
authors.affiliation: Duke-Umstead Bipolar Disorders Program, Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Box 3414, Durham, NC 27710, USA.
authors.forename: Frederick
authors.initials: F
authors.lastname: Cassidy
authors.forename: Bernard J
authors.initials: BJ
authors.lastname: Carroll
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001714:Bipolar Disorder / Q000523:psychology*; D005260:Female; D006760:Hospitalization / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012621:Seasons; D012720:Severity of Illness Index