[Dementia in nonagenarians. Systematic review of population-based studies with Spanish data].

Introduction: Ageing is associated with the quasi exponential getting up of dementia prevalence and incidence until 85 years, but the data in the oldest-old are controversial. AIM. Systematic review of population based studies that analyze prevalence and incidence of dementia in the oldest-old, specifically in nonagenarians.

Patients And Methods: Systematic review in Medline database of population based surveys describing prevalence or incidence in older than 90, published from 1989. 459 papers were identified, but of the 170 population-based detailed reviewed, 41 studies accomplished the inclusion criteria (Pamplona, Gerona and NEDICES Study are included).

Results: The dementia prevalence described in nonagenarians has a range of 25-54%. The dementia incidence in older than 90 has a range of 47-174 cases per 1,000 people/year, being greater in females. In the oldest-old a variable prevalence and incidence of dementia was described in the selected studies. Some authors consider that exist an exponential increase in the dementia prevalence and another ones indicate a slowing of growth in nonagenarians.

Conclusions: This review is concordant with a persistent not exponential increase in prevalence and incidence of dementia in nonagenarians.