Date of Award

12-2023

Document Type

Thesis

Degree Name

Master of Science in Clinical/Counseling Psychology

Department

Psychology

First Reader/Committee Chair

Jones, Jacob

Abstract

Mild cognitive impairment in Parkinson’s disease (PD-MCI) is the continuum from normal cognitive function to dementia. Recent studies suggest that objectively defined subtle cognitive decline (Obj-SCD), which uses non-traditional “process” neuropsychological scores, may be a better pathway to earlier detection of cognitive impairment. Obj-SCD has been defined as the stage where cognition is not impaired, but biomarkers are present or cognitive impairment is minimal but not sufficient to meet MCI or dementia criteria. We examined the longitudinal trajectories of neurodegenerative markers among individuals who are classified as cognitive normal (CN), Obj-SCD, and PD-MCI. Past literature has been inconsistent about the utility of subjective complaints to improve prediction of cognitive decline. Therefore, we investigated the associations between cerebrospinal fluid (CSF) markers with objective (i.e., neuropsychological process scores) and subjective markers as a second aim. Participants from the PPMI study (N=295) were classified as cognitively normal (CN), objectively defined subtle cognitive decline (Obj-SCD), or mild cognitive impairment in Parkinson’s Disease (PD-MCI). Obj-SCD criteria was determined using three neuropsychological alternative/process scores. CSF was collected from participants via a lumbar puncture over 3 annual follow-ups. Samples were analyzed to detect tau (total tau), phosphorylated tau (p-tau), and amyloid beta (ab) using an enzyme-linked immunosorbent assay (ELISA). Tau and ab markers were examined as ratios: tau/ab, p-tau/ab and p-tau/tau. At baseline, 223 (76%) individuals were classified as CN, 46 (16%) were classified as PD-MCI, and 26 (9%) were classified as Obj-SCD. Analyses failed to find any group differences in any of the CSF markers. Regarding aim 2, we found that subjective reports of cognitive difficulties, but not objective process scores, were significantly associated with worse biomarker outcomes (greater amounts of p-tau/ab and tau/ab). Although prior research has indicated that Obj-SCD is a risk factor for PD-MCI, Obj-SCD was not an intermediate group between CN and PD-MCI in CSF markers. Conversely, the association of subjective cognitive complaints with worse biomarker outcomes is consistent with previous findings that subjective complaints may have clinical utility in detecting cognitive decline.

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