Subjective memory complaints at age 90 + in relation to cognition and risk of incident dementia: The 90 + Study

Associations of Subjective Memory Complaints (SMC) with cognition and future dementia are poorly understood in the oldest old (age 90 +), who have high incidence and prevalence of cognitive impairment. This study aims to (1) report SMC frequency, (2) assess cross-sectional associations between SMC and cognitive test scores, and (3) compare the abilities of SMC, Mini-mental state examination (MMSE), and cognitive diagnosis to predict dementia in the oldest old.

The 90 + Study participants without baseline dementia and with baseline SMC, MMSE, at least one other cognitive test, and cognitive diagnosis were included in cross-sectional analysis. A subset of this group with follow-up cognitive diagnosis was included in longitudinal analysis. Cross-sectional association between SMC and cognitive test scores was explored using linear regression. Risk of incident dementia in relation to baseline SMC, MMSE, and cognitive diagnosis was explored using three Cox regression models. Concordance Index (C-index) was used to compare model performance.

In 893 participants with average age 93 years (range 90-102), 43 % had SMC. Cross-sectionally, SMC were associated with lower scores on memory, language, executive function. After 3.5 years of follow-up (range 0.4-16), 325 of 789 participants developed dementia. SMC, compared with no SMC, was associated with twice the risk of incident dementia (HR=2.16, 95 %CI, 1.72-2.72; p < 0.01). SMC predicted incident dementia as well as MMSE (p = 0.12), but not as well as cognitive diagnosis (p < 0.01).

Single SMC question might be useful to identify oldest old with cognitive impairment or at risk of dementia.