Converging mediators from immune and trophic pathways to identify Parkinson disease dementia

Objective: To identify a panel of peripheral inflammatory/immune mediators that could discriminate Parkinson disease with dementia (PDD) from Parkinson disease (PD) without dementia. Methods: Plasma samples from 52 patients with PD and 22 patients with PDD were prepared from freshly collected blood following an institutional review board-approved protocol. A total of 160 proteins were measured using a multiplex antibody array. Plasma alpha-synuclein levels were analyzed by an electrochemiluminescence immunoassay. The main objective of the statistical analyses was to identify PDD discriminants using the plasma protein profile alone or in combination with age. Results: The PD and PDD groups differed significantly in cognitive measurements (Mini-Mental State Examination, Auditory Verbal Learning Test-A7, and Clinical Dementia Rating) and age. The age-adjusted levels of thymus and activation-regulated chemokine (TARC) and platelet-derived growth factor (PDGF)-AA were significantly different between disease groups. The levels of plasma alpha-synuclein significantly correlated with 26 proteins; among them, PDGF-BB, TARC, PDGF-AA, and epidermal growth factor were the highest. Linear discriminant analysis with leave-one-out cross-validation identified a 14-protein panel with age as discriminants of PDD (96% sensitivity, 89% specificity, area under the curve = 0.9615). Conclusions: We showed that multiple proteins that are mediators of growth/trophic and immune response-related pathways had discriminatory power for identifying PDD in patients with PD. Validation of this discovery-based study in longitudinal population-based studies is warranted. Classification of evidence: This study provides Class III evidence that a 14-protein panel plasma assay combined with age has a sensitivity of 96% and a specificity of 89% for PDD. Neurol Neuroimmunol Neuroinflamm 2016;3:e193; doi: 10.1212/NXI.0000000000000193