Cerebrospinal Fluid Correlates of Neuropsychiatric Symptoms in Patients with Alzheimer's Disease/Mild Cognitive Impairment: A Systematic Review

Background: Neuropsychiatric symptoms (NPS) are common, accelerate the conversion to dementia, and are associated with increased caregiver burden in Alzheimer's disease (AD) and mild cognitive impairment (MCI). Objective: The aim of this study is to identify potential associations between the core cerebrospinal fluid (CSF) biomarkers (amyloid/tau) and NPS in AD/MCI. Methods: For this systematic review, four databases, PubMed (1946-2018), Cochrane (2005-2018), EMBASE (1947-2018), and PsycINFO (1806-2018) were searched for relevant observational studies using an extensive list of keywords. English studies were selected for critical appraisal based on our inclusion/exclusion criteria. Inclusion criteria were defined as 1) at least one AD CSF biomarker has been measured; 2) at least one NPS has been assessed; and 3) analysis has been done to examine the association between core AD CSF biomarker and NPS (main outcome) Animal, postmortem, and review studies were excluded. Results: In total, 21 studies qualified for the systematic review. The overall picture regarding the association between NPS and AD CSF biomarkers is conflicting. However, agitation/aggression was significantly and consistently related to core AD CSF biomarkers. Moreover, depression was the only NPS to occasionally be associated with lower core AD CSF pathology. Conclusion: Our study has revealed agitation/aggression as the most consistent NPS related to core AD CSF biomarkers. Future studies are required to focus on other neglected NPS domains such as disinhibition. Moreover, why depression was the only NPS inversely associated with core AD CSF pathology remains to be elucidated. Our study also revealed a great degree of heterogeneity, hence calling for a more standardized objective approach for the evaluation of NPS.