Dissociation of Clinical Outcomes and CSF Proteinopathy Biomarkers in Parkinson’s Disease: Cognitive–Affective Dissociation with Specificity for Tau

<b>Background:</b> Parkinson's disease (PD) is characterized not only by motor dysfunction but also by widespread degeneration across cortico-striatal, limbic, and cortical circuits. Mounting evidence suggests that tau and α-synuclein pathology underlie these processes, though how these proteinopathies translate into affective and cognitive outcomes remains uncertain. Depression and anxiety are highly prevalent in PD, yet the biological correlates of these affective disturbances are poorly defined. <b>Methods:</b> This is a retrospective analysis of existing data from the Parkinson's Progression Markers Initiative (PPMI). Montreal Cognitive Assessment (MoCA), geriatric depression scale (GDS), and State-Trait Anxiety Inventory (STAI) were used to assess cognition, depression, and anxiety in PD, respectively. The CSF biomarkers evaluated were Aβ42, t-tau, and p-tau181, using Elecsys electro-chemiluminescence immunoassays on the cobas e601 platform (Roche Diagnostics). <b>Results:</b> From the 4380 patients who had GDS information, the MoCA test was collected from 438 patients, and 445 from the GDS test for depression, and the STAI screening for anxiety. There were no significant differences in biomarker levels between patients with depression (GDS ≥ 5) and those without (GDS < 5), nor between patients with anxiety (STAI > 40) and those with lower anxiety scores (STAI ≤ 40). In contrast, cognitive outcomes showed clear associations. Patients with cognitive impairment (MoCA < 26) demonstrated higher levels of pTau (<i>p</i> = 0.02) and tTau (<i>p</i> = 0.01), as well as elevated pTau/Aβ42 (<i>p</i> = 0.003) and tTau/Aβ42 (<i>p</i> = 0.002) ratios compared to those with MoCA ≥ 26. In multivariate analysis, both pTau/Aβ42 > 0.022 (OR 4.64, 95% CI 1.67-13.8) and tTau/Aβ42 > 0.26 (OR 4.18, 95% CI 1.6-11.5) remained significantly associated with cognitive decline. In a longitudinal analysis in the first 3 years of follow-up, cognition in PD remained lower than in controls, while CSF p-tau and Aβ42 remained higher in controls. <b>Conclusions:</b> In our cohort, no associations were found between CSF biomarkers and depression or anxiety, underscoring that mood disturbances in PD are likely mediated by alternative mechanisms such as monoaminergic dysregulation, neuroinflammation, and psychosocial factors. By contrast, cognitive performance (MoCA) was clearly linked to tau-related pathology, rather than α-synuclein or Aβ42 alone. While Aβ42 and α-synuclein remain useful for staging and assessing global disease risk, our findings highlight the specificity of tau-related pathology for cognitive outcomes in PD.