Nontraumatic Intracranial Hemorrhage and Risk of Incident Dementia in US Medicare Beneficiaries.

BACKGROUND: To study the risk of incident dementia after a nontraumatic intracranial hemorrhage in a diverse US population and evaluate whether this risk is different for the subtypes of intracranial hemorrhage.

METHODS: We performed a retrospective cohort study using both inpatient and outpatient claims data on a 5% sample of Medicare beneficiaries per year between January 1, 2008 and December 31, 2018. The exposure was a new diagnosis of nontraumatic intracranial hemorrhage, defined as a composite of intracerebral hemorrhage, subarachnoid hemorrhage, and subdural hemorrhage. The outcome was a first-ever diagnosis of dementia. The exposure and outcomes were identified using validated International Classification of Diseases, Ninth and Tenth Revisions, Clinical Modification diagnosis codes. We excluded patients who had prevalent intracranial hemorrhage or dementia to ensure that only incident cases were counted in our analyses. In the primary analysis, we used Cox regression to study the risk of dementia after intracranial hemorrhage, after adjusting for demographics and comorbidities. In secondary analyses, the risks of dementia in different subtypes of intracranial hemorrhage were studied.

RESULTS: Among 2.1 million patients, 14 775 had a diagnosis of intracranial hemorrhage with an incidence rate of 1.2 (95% CI, 1.1-1.2) per 1000 person-years. Incident dementia was diagnosed in 2527 (17.1%) of the 14 775 patients with intracranial hemorrhage and in 260 691 (12.8%) of the 2 033 190 patients without intracranial hemorrhage. During a median follow-up of 5.6 (interquartile range, 3.0-9.0) years, the incidence rate of dementia was 8.6 (95% CI, 8.1-8.9) per 100 person-years among patients with intracranial hemorrhage and 2.2 (95% CI, 2.0-2.4) per 100 person-years among patients without intracranial hemorrhage. In an adjusted Cox regression analysis, intracranial hemorrhage was associated with an increased risk of incident dementia (hazard ratio, 2.0 [95% CI, 1.9-2.2]). In secondary analyses, a higher risk of incident dementia was observed with intracerebral hemorrhage (hazard ratio, 2.4 [95% CI, 2.2-2.5]), subarachnoid hemorrhage (hazard ratio, 1.99 [95% CI, 1.7-2.2]), and subdural hemorrhage (hazard ratio, 1.6 [95% CI, 1.4-1.7]).

CONCLUSIONS: In a large, heterogeneous cohort of elderly US participants, we found that intracranial hemorrhage was independently associated with a 2-fold increased risk of incident dementia. This elevated risk was consistently observed across subtypes of intracranial hemorrhage.