Seasonal Variations in Neurological Severity and Outcomes of Ischemic Stroke　― 5-Year Single-Center Observational Study

Background:Seasonal variations in the severity and outcomes of stroke remain unclarified.Methods and Results:A total of 2,965 acute ischemic stroke patients from a single-center prospective registry were studied. Among the total patients, stroke onset did not vary by season, though it varied with a peak in winter when limited to patients >75 years old (P=0.026), when limited to patients with moderate-to-severe initial neurological deficits (National Institutes of Health Stroke Scale Score ≥10, P=0.014), and when limited to those with cardioembolic stroke (n=1,031, P=0.010). In 1,934 patients with noncardioembolic stroke, stroke onset did not vary by season. After multivariable adjustment, moderate-to-severe neurological deficits were more common in winter (odds ratio 1.37, 95% confidence interval 1.10–1.72) and spring (1.27, 1.01–1.60), and death at 1 year was more common in summer than in fall (1.55, 1.03–2.36); death or dependency (modified Rankin Scale score 3–6) and death or bedridden (score of 5–6) were not differently common among the seasons.Conclusions:Overall ischemic stroke showed a fairly even distribution among the 4 seasons. Cardioembolic stroke was more common in winter. Ischemic stroke patients had more moderate-to-severe initial neurological deficits in winter and spring. Poor clinical outcomes at 1 year were generally similar among the seasons. Ischemic stroke is not necessarily a winter-dominant disease.