Diurnal and seasonal variations in the onset of primary intracerebral hemorrhage in individuals living in Izumo City, Japan

Object. Little is known about the temporal patterns of primary intracerebral hemorrhage (ICH) among the general population. The aim of this study was to examine diurnal and seasonal variations in the onset of ICH in a community-based series. Methods. The study population consisted of 350 patients who presented with primary 1CH for the first time and were treated between 1991 and 1998 in Izumo City, Japan. Among the entire patient population, the onset of hemorrhage was rarely observed during the night and a peak was observed in the late afternoon. In men 69 years of age or younger, the onset of ICH exhibited a bimodal distribution, with an initial high peak between 8:00 and 10:00 a.m. and a second, lower peak between 6:00 and 8:00 p.m. In contrast, in men 70 years of age or older and in women regardless of age, only a single evening peak, between approximately 6:00 and 10:00 p.m., was found, and no morning peak was observed. For the entire patient population (for both sexes), and for men alone, seasonal variations-a peak in winter and a trough in summer-were significant for all age groups combined. This factor was significant for patients 69 years of age or younger, during the daytime hours (8:00 a.m.-8:00 p.m.), and for patients with untreated hypertension; however, it was not significant for patients 70 years of age or older, during nighttime hours (10:00 p.m.-8:00 a.m.), or for treated hypertensive and normotensive patients. In women, no significant seasonal patterns were found, regardless of patient age, time of day at onset of ICH, or the presence of risk factors. Seasonal variations were statistically significant for patients with hematomas larger than 5 ml, but not for those with hematomas 5 ml or smaller. Conclusions. Temporal distributions in the onset of ICH seem to be influenced by patient sex and age. The seasonal partterns of ICH occurrence may result mainly from changes that occur during the daytime, and may also be modified by the presence of untreated hypertension and by the volume of the hematoma.