Cortical gyrification deficits in early-stage Parkinson's disease: the importance of bradykinesia.

Timely, accurate diagnosis of Parkinson's disease is still challenging for clinicians. It is therefore crucial to identify novel biomarkers to better characterize the early stages of the disease. Here, we assessed cross-sectional brain structure differences between healthy control (HC) and Parkinson's disease participants. We also explored potential correlations between brain structure and distinctive Parkinson's disease clinical features. We analysed T1-weighted brain images from 381 Parkinson's disease patients, primarily in the early stages, and 139 HC participants obtained from the Parkinson's Progression Markers Initiative (PPMI) database. The image processing protocol included quantification of several brain structure parameters: grey matter volume (GMV), cortical thickness, gyrification index (GI), sulcal depth and surface ratio. Regarding clinical variables, we gathered the Schwab and England score (as a measure of functional capacity), along with four motor symptom scores (bradykinesia, tremor, rigidity and postural instability) derived from the Movement Disorder Society-Unified Parkinson's Disease Rating Scale (MDS-UPDRS). We found that the left parahippocampal and lingual gyri showed less gyrification in Parkinson's disease patients compared to HC participants. In Parkinson's disease patients, we also identified GI deficits associated with bradykinesia, the main cardinal motor sign, in right parietal (mainly the supramarginal gyrus), temporal and occipital regions. In addition, higher GI and GMV in the occipital cortex were associated with greater functional capacity in Parkinson's disease. In conclusion, the gyrification deficits observed in early-stage Parkinson's disease patients point to the potential value of cortical folding as a biomarker in Parkinson's disease. Our results indicate that GI deficits are closely associated with bradykinesia and impaired functional capacity, possibly reflecting connectivity issues and/or compensatory mechanisms.