Venous thromboembolism and subsequent diagnosis of subarachnoid hemorrhage: a 20‐year cohort study

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.