Lack of independent mood-enhancing effect for dopaminergic medications in early Parkinson's disease.

Background: A direct antidepressant effect has been reported for certain dopaminergic medications used in the treatment of Parkinson's disease (PD).

Objective: To examine whether dopaminergic medications may exert differential effects on mood in early PD.

Methods: We analyzed prospectively-collected 5-year data on 405 early, drug-naïve (at baseline) PD patients enrolled in the Parkinson's Progression Markers Initiative (PPMI) cohort study, initiated on levodopa, dopamine agonists (DAs), or monoamine-oxidase type B inhibitors (iMAO-B) under naturalistic conditions. The outcome for depressive symptoms was the 15-item Geriatric Depression Scale (GDS-15) score. Potential motor and cognitive confounders were measured using the Unified Parkinson's disease Rating Scale (MDS-UPDRS-III) and the Montreal Cognitive Assessment (MoCA). Three statistical models were used to determine medication effects on GDS-15 scores: unadjusted, adjusted, and a marginal structural model.

Results: One-third of patients in this cohort met GDS-15 threshold for clinically-significant depressive symptoms (GDS-15 ≥ 5). There was a marginal positive effect on GDS-15 scores after iMAO-B treatment initiation (-0.35 95%; CI: -0.73, 0.04; p = 0.08). There were no significant interactions between any of the three medication groups, but robust interactions between MoCA scores and both DAs (p = 0.005) and iMAO-B (p = 0.03) use on GDS-15 scores. Specifically, as MoCA scores worsened, DAs yielded a steeper worsening of GDS-15 scores while iMAO-B a moderating effect on GDS-15.

Conclusion: Dopaminergic medications have no direct effect on mood in early, unselected PD patients.