Summary: New research from UNSW reports that 46.5% of people initially diagnosed with Mild Cognitive Impairment (MCI) later tested as “normal” at least once during follow-up assessments.
Source: University of New South Wales
A closer look at Mild Cognitive Impairment (MCI) — especially its subtypes and how symptoms change over time — is essential to understanding which individuals are at highest risk of progressing to dementia, new research shows.
In a longitudinal study, researchers examined how different MCI subtypes evolve and how often people diagnosed with MCI revert to normal cognition. MCI is defined as an observable decline in cognitive abilities, confirmed by tests, in people who are still largely independent in daily life. While MCI is linked to a higher risk of dementia and, for some, represents a transitional stage between typical cognitive aging and dementia, many factors other than neurodegeneration can cause temporary cognitive decline—such as depression, infection, or medication side effects.
Because these causes can be reversible, it is not uncommon for people diagnosed with MCI to later test within normal ranges. However, the study highlights an important nuance: individuals who revert from MCI to normal cognition are not necessarily free from future risk. Some of these individuals can decline again and later progress to dementia.
Dr. Liesbeth Aerts of the Dementia Collaborative Research Centre at UNSW, lead author on the study, emphasizes that the implications of reversion differ by MCI subtype. In particular, reductions in dementia risk after reversion were observed mainly in those with amnestic MCI, the subtype where memory impairment is the dominant complaint.
The study used data from the Sydney Memory and Ageing Study, a prospective community cohort. Researchers followed 705 older adults with four biennial assessments. They found that reversion from MCI was common: nearly half (46.5%) of participants who had MCI at baseline returned to normal cognitive test performance at least once during follow-up.
Although MCI prevalence and subtype distribution remained relatively stable across assessments, transitions between subtypes and reversion events were frequent. Importantly, most participants who developed dementia (83.8%) had been diagnosed with MCI two years prior to their dementia diagnosis, supporting the view that MCI is often a prodromal stage in the pathway to dementia for many people.
Both those who reverted and those with persistent MCI faced increased risk of progressing to dementia compared with participants who did not have MCI at baseline (hazard ratios 6.4 and 24.7, respectively). Yet participants with stable, nonreverting MCI were at higher risk than those who reverted. This difference was strongest for the amnestic subtype: amnestic MCI reverters versus nonreverters had an increased risk ratio (HR 3.3), whereas the effect was not significant for nonamnestic MCI (HR 1.3).
Dr. Aerts notes that cognitive test scores often fluctuate over time, and single “snapshot” assessments can miss this variability. The findings underscore the need for repeated, longitudinal assessments to more accurately identify individuals at high risk and to distinguish temporary causes of decline from progressive neurodegenerative changes.
The study also highlights limitations of current cognitive testing and points to the growing importance of biomarkers—such as brain imaging and chemical markers—that can detect brain changes long before clinical symptoms appear. Detecting early biological changes may allow intervention earlier in the disease course, when preventing or slowing progression could be more feasible.
Source: Gabrielle Dunlevy, University of New South Wales
Image source: Image adapted from the UNSW news release.
Original research: “Effects of MCI subtype and reversion on progression to dementia in a community sample” by Liesbeth Aerts, Megan Heffernan, Nicole A. Kochan, John D. Crawford, Brian Draper, Julian N. Trollor, Perminder S. Sachdev, and Henry Brodaty. Published online May 10, 2017. DOI: 10.1212/WNL.0000000000004015
Abstract (summary)
Objective: To clarify the course of mild cognitive impairment (MCI) by tracking different MCI subtypes, rates of reversion to normal cognition, and progression to dementia in a community sample.
Methods: Stability of MCI subtypes and dementia risk were evaluated over four biennial assessments as part of the Sydney Memory and Ageing Study.
Results: Prevalence of MCI and its subtypes remained relatively stable across assessments, but reversion from MCI and transitions between subtypes were common. Up to 46.5% of participants classified with MCI at baseline reverted during follow-up. Most participants who developed dementia (83.8%) had MCI two years earlier. Both reverters and participants with stable MCI showed elevated risk of progression to dementia compared to those without MCI at baseline (HR 6.4 and HR 24.7, respectively), with higher risk in nonreverters than in reverters (HR 2.5). This pattern was specific to amnestic MCI (reverters vs nonreverters: HR 3.3), while nonamnestic MCI showed no significant difference (HR 1.3).
Conclusion: The study concludes that reversion’s relevance to future dementia risk depends on MCI subtype. Reliable identification of individuals at high risk requires subtype-specific classification and repeated, longitudinal assessment.