Progression and Stability of Cognitive Asymmetry in a Large Sample of Alzheimer's Disease Patients
Alverson, William Alexander
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Previous research has suggested that a significant minority of patients with Alzheimer’s Disease (AD) exhibit asymmetric cognitive profiles (greater verbal than visuospatial impairment or vice versa) and that these patient subgroups may differ in demographic and other characteristics. Prior studies have been relatively small, and this investigation sought to examine correlates of asymmetry in a large patient sample (N=924) and to determine if cognitive asymmetry is stable over time (in smaller subsets of patients). Participants were classified into the following cognitive profile groups: Low Verbal, Symmetric, and Low Visuospatial. Consistent with past research, 27.7% of patients were classified as having asymmetric cognitive profiles, with more patients in the Low Visuospatial subgroup. Low Visuospatial patients were younger than patients in the other subgroups, and Low Verbal patients performed worse on a measure estimating premorbid verbal intelligence. Carrying two copies of the ApoE ε4 allele was associated with having an asymmetric cognitive profile, as expected based on previous literature. Regression analyses consistently found age and the number of ε4 alleles to be significantly predictive of asymmetry. The degree of asymmetry and asymmetry classifications were relatively stable across time, based on correlations and kappa statistics across evaluations, respectively. No patients in either of the asymmetric subgroups changed classification to the opposite asymmetric subgroup over time. Repeated measures ANCOVA (with Asymmetry Index as the dependent variable) yielded significant interactions between baseline asymmetry classification and time. This indicated that the degree of asymmetry in the asymmetric subgroups became smaller (more symmetric) over time, supporting the hypothesis that asymmetry decreases as the disease progresses. These results, considered together, provide evidence for sufficient systematic differences in asymmetry classifications to merit consideration as distinct subgroups of the disease.