Effects of dopaminergic drug adjustment on executive function in different clinical stages of Parkinson's disease

Abstract

Background: Effects of dopaminergic medication on executive function in patients with Parkinson's disease (PD) are inconsistent.

Objective: We examined the effect of dopaminergic medication on executive function in 24 drug-naïve PD patients (de novo group) and in 21 PD patients on chronic dopaminergic medication (chronic medication group).

Methods: PD patients without dementia were included in this study. For the de novo group patients, dopaminergic medication was initiated, and the dose was increased to improve motor symptoms. For the chronic medication group patients, dopaminergic medication was adjusted to relieve clinical problems. All participants were tested prior to and at 4-7 months after the drug initiation/adjustment. Executive function was assessed by using the Behavioral Assessment of the Dysexecutive Syndrome (BADS). Motor function was assessed by using the Unified Parkinson's Disease Rating Scale (UPDRS; part III). Improvement in executive function was compared with a simultaneous change in levodopa equivalent doses (LED) of dopaminergic medication and with improvement in motor functions.

Results: The mean standardized BADS scores showed no significant improvement in both the groups. In the de novo group, percent improvement in the standardized BADS scores showed a significant positive correlation with the LED, but not with percent improvement in UPDRS part III. In the chronic medication group, percent improvement in the standardized BADS scores was negatively correlated with change in the LED, but not with percent improvement in UPDRS part III. Multiple regression analysis using improvement in the standardized BADS score as a dependent variable and patient's background factors (ie, age, education, disease duration, and motor and executive assessments at baseline) as independent variable showed that improvement in the executive assessment is significantly correlated with the LED only in the de novo group.

Conclusion: Effects of dopaminergic drug adjustment on executive function differ according to the patient's clinical stage and depend on LED in de novo stage.

Keywords: correlation between executive improvement and levodopa equivalent dose; dopaminergic drug; inverted U-shaped theory; levodopa equivalent dose; motor disorders.

Figure 1

Distribution of percent improvement in the standardized BADS score and change in the LED in the de novo group. Note: Percent improvement in the standardized BADS score showed a significant positive correlation with the LED (**p<0.01). Abbreviations: BADS, Behavioral Assessment of the Dysexecutive Syndrome; LED, levodopa equivalent dose.

Figure 2

Distribution of percent improvement in the standardized BADS score and percent improvement in UPDRS part III in the de novo group. Note: Percent improvement in the standardized BADS score did not correlate with the percent improvement in UPDRS part III. Abbreviations: BADS, Behavioral Assessment of the Dysexecutive Syndrome; UPDRS, Unified Parkinson’s Disease Rating Scale.

Figure 3

Distribution of percent improvement in the standardized BADS score and change in the LED in the chronic medication group. Note: Percent improvement in the standardized BADS score showed a negative correlation with the change in the LED (*p<0.05). Abbreviations: BADS, Behavioral Assessment of the Dysexecutive Syndrome; LED, levodopa equivalent dose.

Figure 4

Distribution of percent improvement in the standardized BADS score and percent improvement in UPDRS part III in the chronic medication group. Note: Percent improvement in the standardized BADS score showed no correlation with percent improvement in UPDRS part III. Abbreviations: BADS, Behavioral Assessment of the Dysexecutive Syndrome; UPDRS, Unified Parkinson’s Disease Rating Scale.