Background: Venous thromboembolism is a predictor of subsequent risk of ischemic stroke and intracerebral hemorrhage, but no data are available regarding its association with risk of subarachnoid hemorrhage. Objectives: To examine this issue, we conducted a nationwide cohort study in Denmark. Patients and methods: Between 1977 and 2007, we identified 97 558 patients with a hospital diagnosis of venous thromboembolism and obtained information on risk of subsequent subarachnoid hemorrhage during follow-up in the Danish Registry of Patients. The incidence of subarachnoid hemorrhage in the venous thromboembolism cohort was compared with that of 453 406 population control cohort members. Results: For patients with pulmonary embolism (PE), there was clearly an increased risk of subarachnoid hemorrhage, both during the first year of follow-up [relative risk 2.69; 95% confidence interval (CI), 1.32-5.48] and during later follow-up of 2-20 years (relative risk 1.40; 95% CI, 1.05-1.87). For patients with deep venous thrombosis (DVT) the risk was likewise clearly increased during the first year of follow-up (relative risk 1.91; 95% CI, 1.13-3.22), but not during later follow-up (relative risk 1.04; 95% CI, 0.81-1.32). Conclusions: We found evidence that PE is associated with an increased long-term risk of subarachnoid hemorrhage. The two diseases might share etiologic pathways affecting the vessel wall or share unknown risk factors.
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