The prevalence of dementia and its subtypes in an elder community population

Background: Epidemiological studies of dementia subtypes have revealed widely varying distribution rates. There are almost no published community prevalence data for dementia with Lewy bodies (DLB) or the frontal lobe dementias (FLD). Aims: To identify the distribution of dementia subtypes in a representative community population of older people. Method: People aged 65 years and older in randomised enumeration districts in Islington, north London, were screened using a reliable and valid questionnaire. People screened as having dementia were assessed in detail and diagnoses were made according to standard diagnostic criteria. Associations were examined between demographic variables and type of dementia. Results: Of 1085 people interviewed, 107 (9.86%) met screening criteria for dementia. Diagnoses were made for 72 people (67.3%). Distribution of subtypes varied according to the criteria used, the best-validated criteria yielding: Alzheimer's disease 31.3%; vascular dementia 21.9%; DLB 10.9%; and FLD 7.8%. Dementia, and particularly the vascular subtype, was over-represented in people born in Africa or the Caribbean. Conclusions: Alzheimer's disease is confirmed as the most common cause of dementia in older people, followed by vascular dementia. However, DLB and FLD occur sufficiently often to be seen frequently in clinical practice and should be incorporated into future editions of standard diagnostic criteria. Given the differing rates of subtypes according to the diagnostic system used, it is desirable that a degree of consensus be reached on the diagnostic criteria to be employed in future epidemiological research. The excess of dementia in older adults from non-UK countries needs to be addressed