Background: Early treatment of Alzheimer's disease may reduce its devastating effects. By focusing research on asymptomatic individuals with Alzheimer's disease pathology (the preclinical stage), earlier indicators of disease may be discovered. Decreasing cerebrospinal fluid beta-amyloid42 is the first indicator of preclinical disorder, but it is not known which pathology causes the first clinical effects. Our hypothesis is that neuropsychological changes within the normal range will help to predict preclinical disease and locate early pathology.
Methods and findings: We recruited adults with probable Alzheimer's disease or asymptomatic cognitively healthy adults, classified after medical and neuropsychological examination. By logistic regression, we derived a cutoff for the cerebrospinal fluid beta amyloid42/tau ratios that correctly classified 85% of those with Alzheimer's disease. We separated the asymptomatic group into those with (n = 34; preclinical Alzheimer's disease) and without (n = 36; controls) abnormal beta amyloid42/tau ratios; these subgroups had similar distributions of age, gender, education, medications, apolipoprotein-ε genotype, vascular risk factors, and magnetic resonance imaging features of small vessel disease. Multivariable analysis of neuropsychological data revealed that only Stroop Interference (response inhibition) independently predicted preclinical pathology (OR = 0.13, 95% CI = 0.04-0.42). Lack of longitudinal and post-mortem data, older age, and small population size are limitations of this study.
Conclusions: Our data suggest that clinical effects from early amyloid pathophysiology precede those from hippocampal intraneuronal neurofibrillary pathology. Altered cerebrospinal fluid beta amyloid42 with decreased executive performance before memory impairment matches the deposits of extracellular amyloid that appear in the basal isocortex first, and only later involve the hippocampus. We propose that Stroop Interference may be an additional important screen for early pathology and useful to monitor treatment of preclinical Alzheimer's disease; measures of executive and memory functions in a longitudinal design will be necessary to more fully evaluate this approach.