Circadian rhythm pathways are highlighted in a number of etiological models of bipolar disorder (BD). More than 25% of bipolar patients may present seasonal pattern (SP). However, there is very limited scientific data on the prevalence of SP, its clinical manifestations and any gender influence.

Caucasian individuals who met DSM-IV criteria for BD I or II were recruited from three university-affiliated psychiatric departments in France (Paris, Bordeaux, Nancy). SP was defined according to DSM-IV criteria. Clinical and socio- demographic variables were obtained from structured interviews with the patients and their relatives.

Four hundred and fifty-two bipolar patients (n=452) in euthymic state were included in the study, 102 of them (23%) were considered as having SP according to DSM-IV criteria. Multivariate analysis showed a significant association of BD patients with SP for bipolar II subtype (OR=1.99, p=0.013), rapid cycling (OR=2.04, p=0.02), eating disorder (OR=2.93, p=0.003) and the total number of depressive episodes (OR=1.12, p=0.002). 71% of cases were correctly classified by this analysis. However, when stratifying the analyses by gender, SP was associated with BD II subtype (OR=2.89, p=0.02) and total number of depressive episodes (OR=1.21, p=0.002) in males but with rapid cycling (OR=3.02, p=0.003) and eating disorders (OR=2.60, p=0.02) in females.

The high prevalence of SP in BD, its associated clinical characteristics and the observed differences between genders, suggest that SP represents a potentially important specifier of BD.