Cortical thickness changes in patients with Parkinson's disease and impulse control disorders

Introduction: To investigate gray matter (GM) and cortical thickness (CTh) changes in patients with Parkinson's disease (PD) with and without Impulse Control Disorders (ICDs). Methods: Fifteen patients with PD with ICDs (ICD+), 15 patients with PD without ICDs (ICD-) and 24 age and sex-matched healthy controls (HCs) were enrolled in the study. Patients were screened for ICDs by the Minnesota Impulsive Disorders Interview (MIDI) and underwent an extensive neuropsychological evaluation. Whole brain structural imaging was performed on a 3T GE MR scanner. Surface-based investigation of CTh was carried out by using Freesurfer Software. We also used voxel-based morphometry to investigate the pattern of GM atrophy. Results: The voxel-wise analysis of the regional differences in CTh revealed that ICD+ patients showed a statistically significant (p<0.01 FDR) thicker cortex when compared to both ICD- patients and HCs in the anterior cingulate (ACC) and orbitofrontal (OFC) cortices. Moreover, cortical thickness abnormalities were positively correlated with ICD severity (p<0.05 FDR). VBM data did not reveal any statistically significant differences in local GM. Conclusions: Our results demonstrate that ICD+ patients have an increased CTh in limbic regions when compared with ICD- patients at the same disease stage and with an equal daily levodopa equivalent dose. These corticometric changes may play a role in the lack of inhibition of compulsive behaviors. The presence of such structural abnormalities may result from a synergistic effect of dopaminergic therapy in patients with a pre-existing vulnerability to develop an abnormal behavioral response to external stimuli.