Motor asymmetry in Parkinson’s disease: Diagnostic thresholds based on clinical scores and DaTSCAN imaging

Motor asymmetry is a key feature of Parkinson's disease that can influence disease progression and patient outcomes. However, there is currently no consensus on the best method or clear thresholds to determine motor asymmetry, which limits the ability to standardize its assessment across studies. This work aimed to determine which motor asymmetry score - standardized or non-standardized - best predicts dopaminergic damage in the putamen, as measured by DaTSCAN, and to establish clear thresholds for distinguishing symmetric from asymmetric profiles. Data from the Parkinson's Progression Markers Initiative were utilized for the Receiver Operating Characteristic curve analysis. Both motor asymmetry scores significantly predicted dopaminergic asymmetry, with the non-standardized score showing a slightly higher predictive power (area under the curve [AUC] = 0.621, p < 0.001) compared to the standardized score (AUC = 0.569, p = 0.018). For the non-standardized score, a cut-off of ± 2.50 yielded a sensitivity of 0.874 and specificity of 0.783. In contrast, the standardized score achieved a cut-off of ± 0.188, resulting in a sensitivity of 0.908 and specificity of 0.823. These findings underscore the importance of motor asymmetry in clinical evaluations of Parkinson's disease and provide a foundation for further research aimed at refining diagnostic thresholds.