Aneurysmal subarachnoid hemorrhage in Izumo City and Shimane Prefecture of Japan. Incidence.

During the 5-year period from 1980 to 1984, the incidence of subarachnoid hemorrhage due only to rupture of aneurysms was investigated in Izumo City, a small city with a population of 79,026. Additionally, to ascertain the relation of incidence to the size of the geographic area and/or population, a similar analysis was made on a larger area of Shimane Prefecture, including Izumo City, with a total population of 789,712. During this 5-year period, a total of 83 patients with aneurysmal subarachnoid hemorrhage were hospitalized in Izumo City, 548 patients in Shimane Prefecture. Ruptured aneurysms were confirmed in 77 cases (93%) in Izumo City and 466 cases (85%) in Shimane Prefecture. The crude annual incidences of aneurysmal subarachnoid hemorrhage for Izumo City and Shimane Prefecture were 21.0 and 13.9 per 100,000 population for all ages, and the age-adjusted annual incidences (adjusted to the 1980 population of Japan) were 18.3 and 11.0 per 100,000 for all ages, respectively. For both Izumo City and Shimane Prefecture, the age-specific annual incidences peaked at the ages of 50-69 years, and the highest incidence was 92.3 per 100,000 men from Izumo City in the eighth decade of life. The annual incidence of subarachnoid hemorrhage for Izumo City is the highest reported to date. If a wider area, such as Shimane Prefecture, were studied many patients in poor condition, particularly elderly patients, would be missed. To determine accurately the incidence of aneurysmal subarachnoid hemorrhage, it thus might be better to conduct the study in a small city such as Izumo City.