Primary intracerebral and aneurysmal subarachnoid hemorrhage in Izumo City, Japan. Part I: Incidence and seasonal and diurnal variations

Object. The purpose of this community-based study was first to estimate the incidence rates of primary intracerebral hemorrhage (ICH) and aneurysmal s ubarachnoid hemorrhage (SAH) in Izumo City, Japan, and second to investigat e whether there were seasonal and diurnal periodicities in their onset. Methods. During 1991 through 1996, 267 patients with primary ICH and 123 wi th aneurysmal SAH were treated in Izumo City. The crude and the age- and se x-adjusted annual incidence rates per 100,000 population for all ages were 52 and 48 for ICH and 24 and 23 for SAH, respectively. These incidence rate s were higher than those previously published for any other geographical re gion. The incidence rates of both ICH and SAH increased almost linearly wit h age. For ICH, a significant seasonal pattern was observed in men and in p atients younger than 65 years, with a peak in winter and a trough in summer . However, no significant seasonal fluctuation was found in women or in ind ividuals aged 65 years or older. There was no significant seasonal periodic ity for SAH, even when patients were analyzed according to sex and age. Diu rnal variations in the onset of both ICH and SAH were significant (except i n men with SAH), with a nadir between midnight and 6:00 a.m. Conclusions. The actual incidence rates of both primary ICH and aneurysmal SAH seem to be much higher than have been reported so far. In addition, the data indicate the existence of seasonal periodicity for men and younger pa tients with ICH, and that the risk of both ICH and SAH is lower during nigh ttime.