Aggregation of abnormal memory scores and risk of incident Alzheimer's disease dementia: a measure of objective memory impairment in amnestic mild cognitive impairment

Nicholas I. Bradfield*, Kathryn A. Ellis, Greg Savage, Paul Maruff, Samantha Burnham, David Darby, Nicola T. Lautenschlager, Ralph N. Martins, Colin L. Masters, Stephanie R. Rainey-Smith, Joanne Robertson, Christopher Rowe, Michael Woodward, David Ames

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    3 Citations (Scopus)

    Abstract

    OBJECTIVES: The criteria for objective memory impairment in mild cognitive impairment (MCI) are vaguely defined. Aggregating the number of abnormal memory scores (NAMS) is one way to operationalise memory impairment, which we hypothesised would predict progression to Alzheimer's disease (AD) dementia.

    METHODS: As part of the Australian Imaging, Biomarkers and Lifestyle Flagship Study of Ageing, 896 older adults who did not have dementia were administered a psychometric battery including three neuropsychological tests of memory, yielding 10 indices of memory. We calculated the number of memory scores corresponding to z ≤ -1.5 (i.e., NAMS) for each participant. Incident diagnosis of AD dementia was established by consensus of an expert panel after 3 years.

    RESULTS: Of the 722 (80.6%) participants who were followed up, 54 (7.5%) developed AD dementia. There was a strong correlation between NAMS and probability of developing AD dementia (r = .91, p = .0003). Each abnormal memory score conferred an additional 9.8% risk of progressing to AD dementia. The area under the receiver operating characteristic curve for NAMS was 0.87 [95% confidence interval (CI) .81-.93, p < .01]. The odds ratio for NAMS was 1.67 (95% CI 1.40-2.01, p < .01) after correcting for age, sex, education, estimated intelligence quotient, subjective memory complaint, Mini-Mental State Exam (MMSE) score and apolipoprotein E ϵ4 status.

    CONCLUSIONS: Aggregation of abnormal memory scores may be a useful way of operationalising objective memory impairment, predicting incident AD dementia and providing prognostic stratification for individuals with MCI.

    Original languageEnglish
    Pages (from-to)146–157
    Number of pages12
    JournalJournal of the International Neuropsychological Society
    Volume27
    Issue number2
    Early online date10 Aug 2020
    DOIs
    Publication statusPublished - Feb 2021

    Keywords

    • cognitive ageing
    • cognitive neuroscience
    • mild neurocognitive disorder
    • neuropsychology
    • neurocognitive disorders

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