The prevalence of dementia subtypes in rural Tanzania

The prevalence of dementia is predicted to increase rapidly in developing countries. Vascular risk factors may contribute to this rise. Our aim was to estimate the proportions of Alzheimer's disease (ADD) and vascular dementia (VAD) in a prevalent cohort of dementia cases in rural Tanzania.

A two-stage door-to-door dementia prevalence study.

Hai district, Tanzania

In Phase I, the Community Screening Instrument for Dementia (CSI-D) was used to screen 1198 community-dwelling people for dementia. In Phase II, 168/184 (91.3%) of those with poor performance, 56/104 (53.8%) of those with intermediate performance and 72/910 (7.9%) of those with good performance on CSI-D were interviewed and diagnoses were made using the DSM-IV criteria.

For subtype diagnosis, DSM-IV dementia criteria plus NINCDS-ADRDA criteria were used for ADD and NINDS-AIREN criteria for VAD. Other dementias were diagnosed by international consensus criteria. Diagnoses were confirmed or excluded by computerised tomography where clinically appropriate.

Of 78 dementia cases, 38 (48.7%) were ADD and 32 (41.0%) were VAD. The crude prevalence of ADD was 3.7% (95% CI 2.5 to 4.9) and of VAD was 2.9% (95% CI 1.9 to 3.9). The age-adjusted prevalence was 3.0% (95% CI 1.8 to 4.2) for ADD and 2.6% (95% CI 1.6 to 3.6) for VAD. A previous diagnosis of diabetes mellitus was independently associated with greater odds of having VAD than ADD.

VAD accounted for a greater proportion of dementia cases than expected. Further investigation and treatment of risk factors is required in this setting.