[The role of season in the incidence of deep venous thrombosis]. / Rôle de la saison dans l'incidence de la thrombose veineuse profonde.

INTRODUCTION: The question of the role of season as a predisposing factor for development of venous thromboembolic disease still remains a matter of debate. Actually, most reports described a higher incidence of thrombotic disorders in winter, while a recent study showed no seasonal variation in the incidence of deep vein thrombosis (DVT). These data led us to study the seasonal distribution of all outpatients with DVT admitted to our Department over a period of 14 years. METHODS: Retrospective review of the files of all outpatients with confirmed (venography or ultrasound) DVT of the legs admitted from Jan. 1st 1982 to Dec. 31st 1995 (n = 512; mean age 59.4 years; 49.4% women). RESULTS: DVT occurred in spring in 135 (26.4%), in summer in 104 (20.3%), in autumn in 142 (27.7%) and in winter in 131 (25.6%) patients. This distribution appears to be similar to an expected uniform distribution [chi 2(3) df = 6.48; p = 0.090 (NS)]. CONCLUSIONS: In our study, by investigating retrospectively 512 outpatients with confirmed DVT, no correlation was found between season and development of thrombosis, suggesting that cold seasons do not represent a predisposing factor for DVT. Further large prospective studies are needed in order to validate our data and to investigate the clinical implications and the precise role of the season in the risk of occurrence of venous thrombosis.