Cross-sectional and longitudinal associations of motor fluctuations and non-motor predominance with cerebrospinal τ and Aβ as well as dementia-risk in Parkinson's disease

Experimental, neuropathological and cerebrospinal fluid (CSF) studies support τ and amyloid-β (Aβ) relevance in Parkinson's disease (PD) related dementia. Lesser motor fluctuations (MFs) and non-motor features have also been related to PD-dementia. Yet, little is known about the association of MFs and non-motor symptoms with CSF τ and Aβ in PD. We hypothesized that lesser MFs and non-motor predominance are related to these CSF markers and dementia-risk in PD. We studied 58 PD patients (dementia at baseline, n = 21; dementia at 18-months, n = 35) in whom CSF Aβ and τ had been determined with ELISA techniques. MFs and a number of non-motor symptoms (apathy, anxiety, irritability, depression, visual hallucinations, spatial disorientation, memory complaints) over disease course were dichotomized as absent-mild vs. moderate-severe by retrospective clinical chart review blind to CSF findings. Non-motor predominance was defined as ≥ 3 non-motor symptoms (after the cohort-median of non-motor symptoms per patient) with ≥ 2 being moderate-severe and ≥ 1 having been present from onset, with all these being more disabling overall than motor features. Cross-sectionally, CSF biomarkers were non-parametrically compared according to dichotomized MFs and non-motor predominance. Longitudinally, dementia was the outcome (dependent variable), CSF markers, MFs and non-motor predominance were the predictors (independent variables), and potential modifiers as age, sex, and memory complaints were the covariates in binary regression models. Absent-mild MFs were associated with higher CSF τ markers and shorter time-to-dementia, while non-motor predominance and decreasing CSF Aβ independently increased longitudinal dementia-risk. In summary, absent-mild MFs, non-motor predominance and CSF τ and Aβ might define endophenotypes related to the timing or risk of dementia in PD.