title: Clinical and prognostic implications of seasonal pattern in bipolar disorder: a 10-year follow-up of 302 patients.
abstract: BACKGROUND
  More than 20% of bipolar patients may present with seasonal pattern (SP). Seasonality can alter the course of bipolar disorder. However, to date, long-term follow-up studies of bipolar patients presenting with SP are scarce. We present a 10-year follow-up study comparing clinical and demographic features of bipolar patients with and without SP.
  
  
  METHODS
  Three hundred and twenty-five bipolar I and II patients were followed up for at least 10 years. SP was defined according to DSM-IV criteria. Clinical variables were obtained from structured interviews with the patients and their relatives. Patients with and without SP were compared regarding clinical and sociodemographic variables and a stepwise logistic regression was performed.
  
  
  RESULTS
  Seventy-seven patients (25.5%) were classified as presenting with SP, while 225 (74.5%) were considered as presenting with no significant seasonal variation. Twenty-three patients (7%) were excluded from the study because it was unclear whether they had seasonality or not. There were no differences between groups regarding demographic variables. Patients with SP predominantly presented with bipolar II disorder, depressive onset, and depressive predominant polarity. The greater burden of depression did not correlate with indirect indicators of severity, such as suicidality, hospitalizations or psychotic symptoms.
  
  
  CONCLUSIONS
  Our study links the presence of SP with both bipolar II disorder and predominant depressive component. However, we could not find any difference regarding functionality or hospitalization rates. Modifications in the criteria to define SP are suggested for a better understanding of bipolar disorder.
authors.affiliation: Bipolar Disorders Program, Clinical Institute of Neuroscience, Hospital Clinic, Institut d'Investigacions Biomédiques August Pi Sunyer, Barcelona Stanley Foundation Center, Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Goikolea
authors.forename: F
authors.initials: F
authors.lastname: Colom
authors.forename: A
authors.initials: A
authors.lastname: Martínez-Arán
authors.forename: J
authors.initials: J
authors.lastname: Sánchez-Moreno
authors.forename: A
authors.initials: A
authors.lastname: Giordano
authors.forename: A
authors.initials: A
authors.lastname: Bulbena
authors.forename: E
authors.initials: E
authors.lastname: Vieta
mesh_terms: D000203:Activities of Daily Living; D001714:Bipolar Disorder / Q000145:classification* / Q000175:diagnosis* / Q000523:psychology; D003710:Demography; D039721:Diagnostic and Statistical Manual of Mental Disorders; D004651:Employment; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007406:Interview, Psychological; D008016:Life Change Events; D008297:Male; D001523:Mental Disorders / Q000145:classification / Q000175:diagnosis / Q000523:psychology; D008875:Middle Aged; D012621:Seasons; D017678:Sex Distribution; D013997:Time Factors