Frontal functions in depressed and nondepressed Parkinson's disease patients: Impact of severity stages

Severity of Parkinson's disease (PD) and frontal impairment are positively correlated. Testing frontal functions in depressed/nondepressed PD patients with different severity stages may reveal whether depression leads to this impairment. We aimed to relate severity of PD to frontal functional impairment and to test if negative stimuli/depressive symptoms interfered with frontal tasks. The Stroop test and the Emotional Stroop test were performed by 46 PD patients, 18 of whom were depressed. The Hoehn and Yahr scale assessed severity of the disease. We calculated the difference in seconds for each Stroop card and the interference index (C/D) between depressed and nondepressed patients sharing the same severity of disease. The differences among the groups (depressed and nondepressed) according to the severity of the disease (mild and moderate) were compared using the Mann–Whitney test. The depressed patients had a poorer performance on the test than the nondepressed PD patients, although the difference was not statistically significant. In conclusion, there is a clinically relevant but not statistically significant difference on the performance of frontal tasks between depressed and nondepressed PD patients. Neither depression nor the severity of the disease were determinant to the poorer performance on the Stroop and the Emotional Stroop tests.