Spontaneous Reversion of Mild Cognitive Impairment to Normal Cognition: A Systematic Review of Literature and Meta-Analysis

Abstract

Objectives: The issue of subjects with mild cognitive impairment (MCI) reverting to normal cognition (NC) has to date been taken in limited consideration, and no conclusive data are available on the rate of reversion. We aimed at systematically reviewing available longitudinal studies on MCI and meta-analyzing data with the purpose of estimating the proportion of subjects reverting to NC.

Design: We performed a systematic bibliographic search on PubMed, the Cochrane Library, and the ISI Web of Science databases. We included in the review all longitudinal studies on MCI published from 1999 up to November 2015. Only studies with a longitudinal design, a follow-up ≥2 years, enrolling subjects with MCI, and reporting the number or the percentage of subjects reverting to NC were included. Data extraction was performed independently by 2 authors. The methodological quality of studies was also assessed by 2 independent authors using the QUIPS tool.

Results: Twenty-five studies were included. The quality of evidence was found to be moderate. We observed an overall 18% (95% CI 14-22) reversion rate from MCI to NC. Results from the metaregression showed a significant association between effect size and study setting. In particular, estimates significantly varied according to study setting, with an 8% (95% CI 4-11) reversion rate in clinical-based studies and a 25% (95% CI 19-30) rate in population-based studies. The frequency of reversion from MCI to NC further increased to 26% when considering only studies of better quality. Only a few studies were designed to specifically investigate the reversion from MCI to NC, thus relevant information on this topic was frequently missing.

Conclusion: Our data confirm that reversion to normality is a common outcome in subjects with MCI, thus leading to recommend a more balanced view when approaching the construct of MCI both in a clinical and in a research setting.

Keywords: Mild cognitive impairment; dementia; longitudinal studies; overdiagnosis.