The decreasing prevalence of reversible dementias: an updated meta-analysis.

BACKGROUND: In 1988, 2 meta-analyses suggested that the prevalence of reversible dementia was significantly lower than had been previously estimated. It was predicted that further work would indicate an even lower rate. The present study represents an updated meta-analysis of the true prevalence of reversible dementia.
METHODS: MEDLINE was searched from 1987 through 2002. References were also gleaned from pertinent articles and relevant textbooks. Data were extracted on the nature and provenance of the studies, dementia etiology, and the proportion of cases that were potentially reversible and reversed.
RESULTS: Fifty articles were identified of which 39 met the study criteria, representing 7042 patients of whom 5620 (87.2%) had dementia. Patients were classified according to etiology and, where possible (in 23 [59%] of 39 studies), whether the dementia partially or completely resolved. A much higher proportion of studies than was previously the case were either community-based (31%) or observed subjects from outpatient departments (54%). Alzheimer disease was still the commonest cause of dementia (56.3%) followed by a vascular etiology (20.3%). Conditions requiring neuroimaging made up only 2.2% of cases. Potentially reversible causes were seen in 9%, and only 0.6% of dementia cases actually reversed (0.29% partially, 0.31% fully).
CONCLUSIONS: The reported proportion of dementias that reverse is much lower than previously thought. While comorbidity should always be treated for its own sake and in the hope that cognitive decline may at least be delayed, the present findings have significant clinical and economic implications for the workup of dementia.