Topographic pattern of cortical thinning with consideration of motor laterality in Parkinson disease

The asymmetry of Parkinson's disease (PD) may contribute to the unilateral appearance of parkinsonism, as well as its cerebral morphological changes. However, previous studies have not considered that cerebral involvement would probably be asymmetric. Our study aimed to identify whether one-sided symptom dominance has an influence on cortical thinning patterns in early-stage, non-demented PD patients from cortical thickness analyses and cortical thinning patterns are associated with motor functions.

We used cortical thickness analysis in 64 non-demented right-handed subjects: 21 PD patients with left-sided disease onset (LPD), 21 PD patients with right-sided disease onset (RPD) and 22 control subjects. We modeled local cortical thickness as a linear association with each motor symptom.

We identified three clusters exhibiting significant cortical thinning (p < 0.01 RFT corrected) in the LPD group compared with the control group: a cluster including the right primary sensory, motor cortex and paracentral lobule, as well as another two clusters in bilateral parahippocampal gyri. In the RPD group, there was only one cluster that exhibited significant cortical thinning compared with the control group, located in the left lingual gyrus. There were no significant correlations between cortical thinning clusters and motor severity, any of the motor subscales including tremor, rigidity, bradykinesia and axial impairment.

Our right-handed PD population revealed that significant thinning of motor-related cortical areas in contralateral hemisphere to symptomatic side in LPD, but not in RPD group. Our results support that neuroprotective effect of enhanced physical activity by handedness on contralateral motor cortex.