Sex-Specific Incidence of Hemorrhagic Stroke in Japan: An Integrated Population-Based Study

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Background: Intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH) have contrasting epidemiological characteristics, including sex-specific incidence. However, their overall contribution to sex differences in hemorrhagic stroke remains unclear because they are generally evaluated separately. We examined the sex-specific epidemiology of hemorrhagic stroke by integrating ICH and SAH. Methods: We analyzed first-ever ICH and SAH events recorded from 2011 through 2015 in the Shiga Stroke and Heart Attack Registry, a population-based registry covering approximately 1.4 million residents in Japan. Age-specific and age-adjusted incidence rates were calculated by sex and stroke subtype using direct standardization to the 2015 Japanese Census population. Results: Among 4,517 patients with hemorrhagic stroke, 3,461 (76.6%) had ICH and 1,056 (23.4%) had SAH. The age-adjusted incidence of ICH was higher in men than in women (61.2 vs 49.8 per 100,000 person-years), whereas SAH incidence was more than twice as high in women as in men (22.4 vs 10.4 per 100,000 person-years). Despite these opposing patterns, the age-adjusted incidence of hemorrhagic stroke was nearly identical between men and women (71.6 vs 72.2 per 100,000 person-years). ICH accounted for a greater share of the overall incidence among men, whereas SAH accounted for a greater share among women. Conclusions: Despite marked subtype-specific sex differences, the overall incidence of hemorrhagic stroke was similar between women and men. These findings demonstrate that substantial sex differences in individual subtypes may be offset when ICH and SAH are considered together, highlighting the value of an integrated population-level perspective in evaluating sex disparities in hemorrhagic stroke.