Diurnal Variation in Onset of Hemorrhagic Stroke Is Independent of Risk Factor Status: Takashima Stroke Registry

Background: We examined the circadian periodicity of hemorrhagic stroke onset to identify any existing specific pattern and its relationship with conventional stroke risk factors using 14-year stroke registration data. Methods: Data were obtained from the Takashima Stroke Registry, which covers a stable population of approx. 55,000 in Takashima County in central Japan. Out of 499 registered first-ever hemorrhagic stroke events during 1990–2003, there were 429 (186 men, 243 women) events with classifiable onset time. Hemorrhagic stroke incidence was categorized as occurring at night (midnight to 6 a.m.), morning (6 a.m. to noon), afternoon (noon to 6 p.m.) or evening (6 p.m. to midnight). The OR (with 95% CI) of having a stroke in the morning, afternoon or evening were calculated, with night serving as reference. Results: There was significant diurnal variation in hemorrhagic stroke incidence (p < 0.001). The proportion of hemorrhagic strokes was highest in the morning (36.1%, 95% CI: 31.7–40.8) and lowest in the night (11.9%, 95% CI: 9.1–15.3). An excess stroke incidence in the morning was observed in both genders, in subjects <65 years and ≧65 years, and in both intracerebral hemorrhage and subarachnoid hemorrhage. A second surge was also observed during the later part of the day. The higher daytime risk persisted after adjusting for age, gender, and risk factors. Conclusion: In the examination of circadian variation of hemorrhagic stroke onset, a 2-peak temporal distribution was observed, which was independent of conventional risk factors.