Background: the objective of the study was to estimate and compare the incidence rates of ischaemic and haemorrhagic stroke and seizure among cohorts with and without Alzheimer's disease (AD) dementia.

Methods: we conducted a retrospective cohort study using electronic medical records (EMRs) from primary care practices that participated in The Health Improvement Network (THIN) in the United Kingdom from 1 January 1990 to 31 July 2009. For each AD-dementia patient, we selected one general population control patient without AD-dementia matched to one AD-dementia patient on year of birth, sex and physician practice.

Findings: the AD-dementia cohorts were 68% female and averaged 80 years of age at the start of follow-up. Populations for analysis included 19,902 AD-dementia and matched non-AD-dementia patients with no history of stroke at baseline in which 790 incident cases of stroke occurred, and similarly, 22,084 AD-dementia and matched patients with no history of seizure at baseline in which 286 cases of seizure occurred. After adjusting for risk factors for each outcome, hazard ratios comparing AD-dementia with non-AD-dementia patients indicated higher rates among AD-dementia patients for stroke (HR = 1.29, 95% CI 1.11, 1.50) and seizure (HR = 5.31, 95% CI 3.97, 7.10). For stroke and seizure, the incidence rate ratios comparing AD-dementia patients with non-AD-dementia controls were greatest for the younger age groups. AD-dementia was observed to be a risk factor for both haemorrhagic stroke and seizures. Increasing age was associated with a decrease in relative risk and an increase in absolute risk.