Circadian and seasonal occurrence of subarachnoid and intracerebral hemorrhage

Objective: To determine whether the time of onset of subarachnoid hemorrhag e (SAH) or intracerebral hemorrhage (ICH) is associated with a time of day or season of year. Background: Prior studies have suggested that there may be a circadian and seasonal pattern of ischemic stroke occurrence, but this is less certain for hemorrhagic stroke. Population-based data have been un available. Methods: All incident ICH and SAH among residents of Rochester, MN, were ascertained. The medical records of patients were reviewed to dete rmine the time of onset and date of occurrence. The day was divided into 8- hour periods, and the year into seasonal quartiles. Each patient was assign ed a period based on the time of onset of symptoms. The data were analyzed by chi (2) analysis to determine whether there was a trend toward increased occurrence based on time period or seasonal quartile of onset. Results: Fr om 1960 to 1989, there were 155 cases (48 men, 107 women) of incident SAH. From 1975 to 1989, there were 137 cases (57 men, 80 women) of incident ICH. There was a significant increase in the time of onset for ICH and SAH in t he 8 AM to 4 PM period (p = 0.005 and p = 0.03, respectively). The concomit ant occurrence of hypertension, gender, and age did not affect the time of day of occurrence. In the analysis of seasonal variation, there was a signi ficant increase in events during December, January, and February in the com bined SAH and ICH group (p = 0.032) and a trend for SAH alone (p = 0.07) bu t not for ICH (p = 0.34). Hypertension and age had no impact on the associa tion between season and the occurrence of SAH and ICH. Conclusion: The occu rrence of SAH and ICH is increased from 8 AM to 4 PM. The occurrence of hem orrhage is increased during the winter months, but this is likely limited o nly to SAH.