Incidence and subtypes of dementia in three elderly populations of central Spain

Objective: To assess age-, gender, and subtype-specific incidence rates of dementia in three populations in central Spain using data from the Neurological Disorders in Central Spain (NEDICES), a population-based survey of elderly participants. Methods: Individuals were evaluated at baseline (1994-1995) and at follow-up (a median of 3.2 years later in 1997-1998). The evaluation included a screening questionnaire for dementia and a neurological assessment, when possible. Results: Of 5278 participants evaluated at baseline, there were 306 prevalent dementia cases. One hundred and sixty-one incident dementia cases were identified among 3,891 individuals assessed at follow-up. The large majority had Alzheimer's disease (AD): 115 (71.4%) AD, 18 (11.2%) vascular dementia (VaD), 11 (6.8%) dementia associated with parkinsonism, 11 (6.8%) undetermined etiology, and 6 (3.7%) secondary dementia. Average annual incidence rates (per 1,000 person-years) in the population aged 65 to 90 and over years, adjusted to the standard European population, were 10.6 (95% CI, 8.9 to 12.3) for dementia, 7.4 (95% CI = 6.0 to 8.8) for AD, and 1.4 (95% CI = 0.6 to 2.3) for VaD. Age-specific incidence rates of dementia and AD increased exponentially with advancing age. Age, stroke and illiteracy were independent risk factors for dementia and AD. Aggregation of vascular risk factors was related to a higher risk of both VaD and AD. Conclusions: In the NEDICES study, incidence of dementia increased with age beyond age 85 and AD was the most frequent type of dementia. The risk of AD and VaD increased with the number of vascular risk factors.