The Association of Cerebrospinal Fluid Biomarkers of Alzheimer’s Disease with Cognitive Intra-Individual Variability

Abstract Objective Cognitive intra-individual variability (IIV) is a sensitive predictor of cognitive decline and disease severity in Alzheimer’s disease (AD). Despite its sensitivity, whether IIV is merely a psychometric artifact or disease pathology biomarker remains unknown. The present study evaluated the association between IIV and cerebrospinal fluid (CSF) biomarkers of AD. Method Participants included 422 individuals from the National Alzheimer’s Coordinating Center Unified Dataset 3.0 who completed baseline neuropsychological assessment and had CSF data. All participants were adult monolingual English speakers. Participants with vision or hearing impairments were excluded. Cases were stratified into cognitively normal (n = 267) and AD groups (n = 155; mild cognitive impairment = 50, dementia = 105). Cross-sectional IIV was calculated by obtaining the individual standard deviation (iSD) of ten cognitive tests. Finally, the coefficient of variation (CoV) was computed by dividing iSD by the participant’s overall test battery mean. Non-parametric Spearman-rank correlations were used to assess the relation between CoV and CSF biomarkers, including beta-amyloid 1–42, total tau (t-tau), and phosphorylated tau (p-tau181). Results In the AD group, CoV was positively correlated with p-tau181 (r = 0.285, p = 0.003) and t-tau (r = 0.241, p = 0.009), and negatively correlated with beta-amyloid 1–42 (r = −0.314, p < 0.001). Correlations between CoV and CSF biomarkers were not significant in the cognitively normal group for beta-amyloid 1–42 (r = 0.076, p = 0.215), p-tau181 (r = −0.014, p = 0.840), and t-tau (r = −0.046, p = 0.485). Conclusions In people with mild cognitive impairment and dementia of presumed AD etiology, cognitive IIV is associated with CSF biomarkers. These findings provide preliminary evidence that IIV is not merely a statistical artifact, but is associated with AD neuropathology.