Seasonal Variation in Neurological Severity and Clinical Outcomes in Ischemic Stroke Patients ? A 9-Year Study of 5,238 Patients ?

Background: Because the effects of extreme weather conditions on stroke severity and outcomes are unclear, we evaluated seasonal variations in stroke severity and clinical outcomes.Methods and Results: Between 2012 and 2020 we enrolled 5,238 patients with acute ischemic stroke, who were divided into 4 seasons according to stroke onset: spring, summer, autumn and winter. We analyzed the effect of season on the severity and outcomes of all subjects. Multivariable analysis showed that the winter group had 1.234-fold increased risk of moderate-to-severe neurological deficits than the summer group (95% confidence interval (CI): 1.034-1.472, P=0.020). Compared with the summer group, the winter and the spring groups experienced 1.243-and 1.251-fold the risk of suffering from worse outcomes among all patients at 6-month follow-up (95% CI 1.008-1.534, P=0.042, 95% CI 1.013-1.544, P=0.037). The 1-year follow-up revealed similar results. Further comparison of each season in the 2012-2015 and 2016-2020 periods found that the proportion of poor outcomes in the latter autumn group was lower than that in the former time period, with significant differences in both 6-month and 1-year follow-up.Conclusions: The onset season was related to the severity and clinical outcomes of ischemic stroke. Patients with winter onset had more severe neurological deficits and worse outcomes than those with summer onset.