Objective: To investigate whether levodopa (LD) dosing regimen influences the dynamics of repetitive maximal tongue pressure (MTP) in patients with Parkinson’s disease (PD).

Background: Reduced MTP contributes to dysarthria and dysphagia in PD. Dopaminergic therapy improves motor symptoms, but its effects on repetitive orolingual force generation remain unclear. Continuous dopaminergic stimulation (CDS) and intermittent LD dosing (IDS) may differently affect motor output stability via distinct scaling mechanisms.

Method: Fourteen PD patients were studied: ten received IDS and four received CDS (levodopa–carbidopa intestinal gel, n=2; foslevodopa/foscarbidopa infusion, n=2). MTP was measured 20 times per trial at 10-second intervals. For each trial, peak MTP, area under the curve (AUC) of the MTP waveform, and total task time (TTT, total duration to form the MTP waveform) were calculated. Trial-level metrics were analyzed across repetitions using linear mixed-effects models with trial × group interaction as the primary effect, including random intercepts and slopes, adjusted for disease duration and LEDD. Degrees of freedom were estimated via the Kenward–Roger method.

Results: Age, LD daily dose, LEDD, UPDRS-III, and MoCA-J did not differ between groups. A significant trial × group interaction was observed for AUC (F=14.16, p=0.0027). Simple slope analysis showed no change across trials in IDS group (β=−0.043, p=0.71), whereas CDS group exhibited a significant decline (β=−0.837, p=0.0005), remaining significant after adjustment. Baseline AUC did not differ between groups (p=0.51). Peak MTP showed no significant trial × group interaction. TTT showed a modest time effect without treatment interaction. These findings indicate LD dosing regimen affects the ability to sustain orolingual force, relevant for optimizing speech and swallowing rehabilitation in PD.

Conclusion: Repetitive MTP dynamics differ according to LD dosing regimen. The progressive decline in AUC in CDS suggests reduced ability to sustain tongue force despite preserved peak force, possibly reflecting altered basal ganglia–mediated scaling or reduced phasic dopaminergic modulation. Tailoring dopaminergic therapy may improve interventions targeting speech and swallowing deficits in PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/levodopa-dosing-regimen-influences-repetitive-tongue-force-maintenance-in-parkinsons-disease/