Cerebrospinal Fluid Biomarkers and Rate of Cognitive Decline in Very Mild Dementia of the Alzheimer Type

Background Cerebrospinal fluid (CSF) levels of Aβ peptide 1-42 (Aβ 42), tau, and phosphorylated tau (ptau) are potential biomarkers of Alzheimer disease. Objective To determine whether Aβ 42, tau, and ptau predict the rate of cognitive change in individuals with very mild dementia of the Alzheimer type (DAT). Design Retrospective analysis of CSF biomarkers and clinical data. Setting An academic Alzheimer disease research center. Participants Research volunteers in a longitudinal study of aging and cognition. Participants (n = 49) had a clinical diagnosis of very mild DAT with a Clinical Dementia Rating (CDR) of 0.5 at the time of lumbar puncture. All the participants had at least 1 follow-up assessment (mean [SD] follow-up, 3.5 [1.8] years). Main Outcome Measures Baseline CSF levels of Aβ 42, Aβ 40, tau, and ptau at threonine 181 (ptau181) and the rate of dementia progression as measured using the CDR sum of boxes (CDR-SB) score and psychometric performance. Results The rate of dementia progression was significantly more rapid in individuals with lower baseline CSF Aβ 42 levels, higher tau or ptau181 levels, or high tau: Aβ 42 ratios. For example, the annual change in the CDR-SB score was 1.1 for the lowest 2 tertiles of Aβ 42 values and 0.3 for the highest tertile of Aβ 42 values. Conclusions In individuals with very mild DAT, lower CSF Aβ 42 levels, high tau or ptau181 levels, or high tau:Aβ 42 ratios quantitatively predict more rapid progression of cognitive deficits and dementia. Biomarkers of CSF may be useful prognostically and to identify individuals who are more likely to progress for participation in therapeutic clinical trials.