Differentiation between Stroke Subtypes and the Causes of Monthly Variations: The Akita Stroke Registry

OBJECTIVE: It has been established that stroke occurrence is influenced by seasonality. Stroke is divided into three subtypes: cerebral hemorrhage (CH), cerebral infarction (CI), and subarachnoid hemorrhage (SAH). The purpose of this paper was to analyze stroke events by subtype and month, in order to clarify the biggest factors that affect seasonal differences and thereby gain insight into stroke prevention. METHODS: Initial stroke events in the Akita Stroke Registry from 1991 to 2010 (58,684 cases; male 30,549, female 28,135) were classified by subtype and the month of onset, and correlations were estimated based on 115 healthy volunteers' monthly mean resting blood pressure (BP) at home and outdoor temperature measured by the Akita Meteorological Observatory in 2001. RESULTS: Systolic BP showed monthly variation in both morning and evening measurements. BP and outdoor temperature showed significant correlations with hemorrhagic stroke events by month (CH: r=0.87, r=－0.82; SAH: r=0.68, r=－0.82). Among the stroke subtypes, seasonal differences were the greatest in CH. Systolic BP was the most important factor for monthly and seasonal variation in stroke events. By comparing monthly BP variations with CH incidence throughout the year, we concluded that a decrease in home BP of 5 mmHg can reduce the risk of CH by 35%. CONCLUSION: Our findings suggest that lowering BP would be the best strategy for CH prevention. Simple daily actions may be affected by cold stress. As physicians, we must strive to help patients lower their BP throughout the year not only with medication but with lifestyle guidance, especially in winter.