Conversion and Reversion Rates in Japanese Older People With Mild Cognitive Impairment

Approximately 25% of individuals who are diagnosed with amnestic mild cognitive impairment (aMCI) revert to normal cognition (NC) rather than progressing to Alzheimer disease (AD). However, the prevalence of progression and reversion among older people in Asia remains unclear.

A prospective cohort study.

A community in Japan.

A total of 4153 individuals without dementia aged ≥65 years were classified as having NC, aMCI single domain (aMCIs), non-aMCI single domain (naMCIs), aMCI multiple domain (aMCIm), non-aMCI multiple domain (naMCIm), or global cognitive impairment (GCI).

The National Center for Geriatrics and Gerontology-Functional Assessment Tool and the Mini-Mental State Examination were used to conduct cognitive screening. The participants completed baseline (August 2011 to June 2012) and follow-up (August 2015 to June 2016) assessments. We followed up monthly for newly incident AD, as recorded by the Japanese National Health Insurance and Later-Stage Medical Care systems. Multiple imputation was used to adjust for selection bias and loss of information.

At 4-year follow-up, the reversion rates to NC in aMCIs, naMCIs, aMCIm, naMCIm, and GCI were 38.7%, 57.0%, 25.7%, 20.9%, and 43.7%, respectively. Of the participants with NC, aMCIs, naMCIs, aMCIm, naMCIm, and GCI at baseline, 4.7%, 4.5%, 13.1%, 20.6%, 21.6%, and 14.3%, respectively, were subsequently diagnosed with AD. We found significant associations between incident AD and naMCIs [hazard ratio (HR) compared to NC: 2.18, 95% confidence interval (CI): 1.45-3.26], and between AD and aMCIm (HR: 4.39, 95% CI: 2.06-9.39) and between AD and naMCIm (HR: 3.60, 95% CI: 2.13-6.08). However, the association between incident AD and aMCIs and between AD and GCI did not reach significance.

Reversion to NC from MCI and GCI was frequent, and individuals with aMCIs and GCI did not show higher risk of incident AD than those with NC. Older adults with multiple cognitive impairments may be potential targets for preventing dementia.