Different patterns of acute saccadic response to levodopa in de novo Parkinson’s disease

Background: L-dopa (LD) effects on visually guided saccades (VGS) have been poorly investigated in de novo Parkinson's disease (PD) patients through a standardized acute challenge test. Objectives: To assess the acute saccadic effects of LD as well as possible different patterns of VGS response to LD in a consistent population of de novo PD. Methods: VGS were assessed among de novo PD at baseline and 2 h after the administration of LD/carbidopa 250/25 mg. Baseline instrumental assessments were compared with healthy controls (HCs). Results: Thirty-two de novo PD and 17 HCs were enrolled. PD patients showed lower upward velocities and amplitude than HCs, improving after LD administration. Two subgroups were identified among PD patients based on percent improvement or worsening of the most significant changing VGS parameter after LD administration: Group A (19 patients, showing improvement) and B (13 patients, showing worsening). Group A had at baseline reduced vertical, especially downward, velocities, gain and amplitude compared to Group B, with a significant improvement after LD. Conversely, in Group B, an LD-induced worsening effect on both horizontal and vertical VGS parameters was found. Comparing the two identified groups based on clinical-demographic characteristics, higher prevalence of female sex was found in Group B. Conclusions: De novo PD patients presented prominent vertical VGS impairment which improved acutely after LD administration. Different patterns of acute saccadic responses to LD were also shown, suggesting a possible role of VGS in PD phenotyping.