Around one-quarter of individuals who are diagnosed as having amnestic mild cognitive impairment (aMCI) subsequently revert to normal cognition rather than progressing to Alzheimer disease (AD) or other dementias, according to a new meta-analysis published in Alzheimer Disease & Associated Disorders.

Credit: NPG

MCI has attracted considerable attention in recent times, owing to the prevailing view that disease-modifying treatments for AD are likely to be most effective if administered early in the disease course. However, whether MCI can be considered as an early manifestation of AD remains controversial.

“For several years now, clinicians and researchers have noted that the diagnosis of MCI is somewhat unstable,” explains Michael Malek-Ahmadi, who performed the meta-analysis. “The issue of diagnostic instability may have a big impact on determining the efficacy of disease-modifying treatments for AD.”

For his meta-analysis, Malek-Ahmadi selected 25 studies that had an observational and longitudinal design, and did not include patients who were participating in treatment or intervention trials. When the data from all 25 studies were combined, the overall rate of reversion from aMCI to normal cognition was calculated to be 24%.

a substantial discrepancy was observed between clinic-based and community-based studies

Intriguingly, a substantial discrepancy was observed between clinic-based and community-based studies, with reversion rates of 14% and 31%, respectively. Malek-Ahmadi suggests that individuals who present to a memory clinic are likely to be showing early signs of a dementing illness, and might, therefore, have a reduced capacity for cognitive improvement.

“The results of this meta-analysis are important in light of our efforts to identify individuals with MCI in which the underlying cause is AD pathology,” concludes Malek-Ahmadi. “Accurate identification of these individuals will be extremely important as we continue to test disease-modifying therapies that target AD pathology in the brain.”