「人口動態統計」から見たくも膜下出血—年齢，性による変化

Subarachnoid Hemorrhage in 'Vital Statistics of Japan', 1993-1995 : variability with age and sex

I．はじめに

　未破裂動脈瘤の発見は脳ドックの主要な目的となっている．検査前に受診者に対し，くも膜下出血が，どの程度危険な病態であるかを具体的に示すことは必要不可欠なことである．その際，くも膜下出血の発生も，それによる死亡も年齢，性により変化することに留意する必要がある．それを示す方法として，剖検などによる動脈瘤の発生率^{2,12,20,21）}，未破裂動脈瘤の破裂の確率^5,6,22），また，コホート調査など疫学的研究^{1,3,4,8,13,15,16,18,19）}，複数の病院の共同研究による臨床データ^7,9）などが有用である．しかし，いずれも結果にかなりのばらつきがあること，日本では大規模な臨床研究は行われていないこと，またコホート調査は対象の数が少ないために，年齢や性による変化を知ることや，他の死因との比較が充分できないことなどが難点である．

　それに対して，厚生省発行の「人口動態統計」^10）による死亡統計は，死亡例だけのデータであるが，全数統計であるため日本全体のくも膜下出血の傾向を知るのに有用である．くも膜下出血については昭和26年以降各年の死亡数が，性別，5歳毎の年齢階級別にまとめてあり同疾患について得られる最大のデータベースといえる．

The incidence and death rate of subarachnoid hemorrhage (SAH) varies with age and sex. Female pre-ponderance in the incidence of SAH is a well-known fact. However, the degree varies with age. Autopsy.data, records of natural history of unruptured aneurysms, epidemiological and clinical cooperative studieshave provided a great amount of information regarding the statistics of subarachnoid hemorrhage. But,each individual study has its own limitation, such as a bias in case selection in autopsy or clinical studies,predominance of aged population in the epidemiological cohort studies, limited frequency in the detectionof unruptured aneurysms in the entire population. These shortcomings are reflected in the variability in thestatistical data of these studies.

Death records in 'Vital Statistics of Japan', published annually by Ministry of Health and Welfare ofJapan, exhibit the numbers of deaths by cause (according to ICD-9 or 10 code), sex and age. In this study,we calculated the death rates of SAH (per 100,000) in 1993-1995 for each age group of both sexes basedon tlle published data. Deaths from breast cancers and automobile accidents (AMA) were assessed in thesame manner and compared with the results of SAH. The annual death rate of SAH for all peopie inJapan is 10.7 per 100,000 population and the average age of death is 65.6 y.o. The death rate is 8.2 for men,and 13,1 for women. Average age at the death is 60.2 y.o. in men, and 68.8 y.o. in women (p＜0.001). Theage-adjusted death rate to 1985 Japanese population was 7.3 for men and 9.2 for women. Below age 60,rate of death caused by SAH is higher for men than women, but the ratio reverses in the population over60. For men, the death rates after the age of 40,50,60 and 70 were 16.4,20.4,24.1 and 29.2 respectively.For women, the rates were 25.0,32.8,44.1 and 62.4, The female-to-male ratio of the death rates increaseswith age. Female sex should be considered as a risk factor for death from SAH. Number of deaths frombreast cancers was about 90% of those from SAH in women. There was a difference in the age distribu-tion; deaths caused by breast cancer tend to occur in younger age than those caused by SAHs. Mean ageof death was 59.3 for breast cancer and 68.8 for SAH, Deaths caused by SAH is 1.4 times more likely tooccur than those by breast cancer for a 50 year-old woman for the rest of her life, 1.9 times for a 60 y.o.woman, and 2.7 times for a 70 y.o, woman. Regular examination to detect breast cancer is widely per-formed in Japan among elderly women. We believe that a similar screening effort should be targeted forunruptured aneurysms from the standpoint of the medico-social cost.

Automobile accidents (AMA) victimize as many people as SAH in Japan, about 13,000 per year. Formales over the age of forty, AMA victims are more than those from SAH. However, conversely females'deaths from SAH occur three times frequently as those from AMAs. The fact should be taken into consid-eration when screening for unruptured aneurysms.