Associations of cognitive intraindividual variability with Alzheimer's disease risk: A systematic review.

In 30 seconds

This systematic review synthesised 44 studies of cognitive intraindividual variability (IIV)—inconsistency or dispersion across cognitive measures—in relation to Alzheimer’s disease (AD) risk. Nineteen studies examined inconsistency, 23 dispersion, and two both. Greater inconsistency was broadly associated with more severe cognitive impairment, particularly mild cognitive impairment (MCI) and AD dementia. Dispersion findings were mixed but generally linked higher IIV with MCI and predicted incident dementia. Both measures were associated with AD biomarkers, including amyloidosis. Associations with impairment, decline, and biomarkers were reported even after adjustment for mean cognitive performance.

Key findings

• Of 44 studies, 19 examined inconsistency, 23 dispersion, and 2 examined both IIV metrics.
• Greater inconsistency was broadly associated with more severe impairment, particularly in MCI and AD dementia.
• Dispersion findings were mixed, but higher IIV was generally associated with MCI and predicted incident dementia.
• Both IIV metrics were associated with AD biomarkers, including amyloidosis, and findings persisted after adjustment for mean cognitive performance.

Why it matters

Cognitive variability may provide information about impairment and dementia risk beyond average cognitive performance, and its reported links with AD biomarkers may help clarify its relevance to disease processes. The review supports further consideration of IIV as a potential risk-identification measure, while differences in assessment methods currently limit comparisons across studies.

What to keep in mind

The review reports a lack of consensus on IIV assessment methods, complicating direct comparisons; findings for dispersion were mixed.