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Etiology

Risk factors for subarachnoid hemorrhage were hypertension and current smoking for men and women and low body mass for women

ACP J Club. 1992 May-June;116:90. doi:10.7326/ACPJC-1992-116-3-090


Source Citation

Knekt P, Reunanen A, Aho K, et al. Risk factors for subarachnoid hemorrhage in a longitudinal population study. J Clin Epidemiol. 1991 Sep;44:933-9.


Abstract

Objective

To identify the predictors of subarachnoid hemorrhage.

Design

Cohort study.

Setting

34 rural, semiurban, and industrial communities in Finland.

Patients

Between 1966 and 1972, whole communities or random samples of individuals ≥ 15 years of age were invited to participate in a health survey. 23 132 men and 19 730 women between 20 and 69 years of age participated (86% of those invited), were followed for 12 years, and were included in this report.

Assessment of risk factors

Each participant completed a self-administered questionnaire and had a physical examination and laboratory tests. They were classified as definitely hypertensive (systolic blood pressure [SBP] ≥ 170 mm Hg and diastolic [DBP] ≥ 100 mm Hg or taking antihypertensive drugs); moderately hypertensive (SBP ≥ 160 and DBP ≥ 95, but not definitely hypertensive); borderline hypertensive (pressure between moderate hypertension and normotension); or normotensive (SBP < 140 and DBP < 90). Morbidity was followed through the Finnish hospital discharge register and mortality through death certificates. In a subset of 17 913 participants followed an average of 5 years, a neurologist examined clinical records and agreed with 32 of the 36 registered cases of subarachnoid hemorrhage.

Main results

102 men and 85 women had a subarachnoid hemorrhage during the 12-year follow-up, for an incidence of 37/100 000 person-years. Patients with both fatal and nonfatal cases tended to be older, leaner, and more often smokers and hypertensive than other participants. The age-adjusted relative risk (RR) increased in a step-wise fashion with the severity of hypertension; the RRs for borderline, moderate, and definite hypertension among women were 2.0 (95% CI 1.1 to 3.8), 5.4 (CI 2.2 to 13.2), and 5.6 (CI 2.8 to 11.2); and among men, 1.1 (CI 0.7 to 1.6), 1.7 (CI 0.7 to 4.4), and 2.2 (CI 1.1 to 4.4). Risk also increased for current smoking in both men (RR 2.3 [CI 1.5 to 3.5]) and women (RR 2.4 [CI 1.4 to 4.0]). Relative risk fell with increasing body mass index among women (RR 0.7 for women in the middle and highest body mass index groups). On multivariate analysis, when all 3 risk factors were present (hypertension, current smoking, and lean body mass), the RR was 6.7 (CI 2.3 to 19.7) for men and 18.3 (CI 7.8 to 42.7) for women. No excess risk was associated with cholesterol or hematocrit levels, diabetes, or heart disease (but the latter 2 were uncommon).

Conclusion

Hypertension, current smoking, and low body mass (the latter in women) were risk factors for subarachnoid hemorrhage.

Source of funding: National Cancer Institute .

Address for article reprint: Dr. P. Knekt, Social Insurance Institution, P.O. Box 78, SF-00381 Helsinki, Finland.


Commentary

Subarachnoid hemorrhage is the only major type of stroke that has not declined in incidence. It strikes earlier than other types of stroke, and over half the patients die or are disabled. These facts make prevention particularly important.

Hypertension and smoking have been previously shown to represent risks for subarachnoid hemorrhage particularly among women. The finding of an inverse relationship between risk and body mass index, however, is new.

The main advantage of the study is that it was carried out on a large, well-defined population in a country where most patients with subarachnoid hemorrhage come to neurologic and neurosurgical attention, making a correct diagnosis more likely. This theory is supported by the finding of 89% positive predictive value of the diagnosis of subarachnoid hemorrhage from the records when reviewed by a neurologist. The authors, however, provide no data on how many cases were missed because they were not given the diagnosis in the first place. This point is particularly important because up to half of patients eventually presenting with a major subarachnoid hemorrhage will have had a minor and often missed "sentinel bleed."

A causal relation between smoking and hypertension and subarachnoid hemorrhage is plausible because smoking affects vascular elastin and hypertension damages blood vessels. Thinness as a risk is more difficult to fathom. Although thinness is associated with decreased longevity (1), it remains unclear whether thinness is a cause or a marker of earlier mortality. The authors make no comment on the familial incidence of subarachnoid hemorrhage nor on the body characteristics of the patients' close relatives.

This study provides further grounds for the prompt and vigorous treatment of hypertension, for an activist attitude toward cessation of smoking, but also for an open-minded stance toward ideal body weight.

Vladimir Hachinski, MD, DSc(Med)
University of Western OntarioLondon, Ontario, Canada

Vladimir Hachinski, MD, DSc(Med)
University of Western Ontario
London, Ontario, Canada


Reference

1. Sidney S, Friedman GD, Siegelaub AB. Thinness and mortality. Am J Public Health. 1987;7:317-21.