Analyzing the ‘Bradykinesia Complex’ in Parkinson's Disease

Background: Bradykinesia is the hall- mark sign of parkinsonism. We recently proposed redefining bradykinesia as a complex of motor abnor- malities, each reflecting separate pathophysiological elements. Objective: To analyze the ‘bradykinesia complex’ in Parkinson’s disease (PD) and healthy elderly individuals. Methods: We conducted a finger-tapping kinematic anal- ysis in 350 individuals (192 PD patients OFF medication and 158 healthy controls). A subsample of 129 patients was also tested ON medication. Group comparisons were followed by unsupervised clustering. Receiver operating characteristic (ROC) analyses defined optimal kinematic cut-offs to detect individual motor abnormalities. We then quantified the prevalence and combinations of these fea- tures per subject. Using Bayes’ theorem, we estimated the probability of PD based on the observed combination of bradykinesia features. Regression analyses served to identify predictors of kinematic alterations. Results: Patients exhibited reduced velocity and ampli- tude as well as altered rhythm and sequence effect com- pared with controls (all P-values < 0.001). Cluster analysis revealed substantial group overlap. ROC analyses showed that bradykinesia (movement slowness) was the most common and accurate feature for distinguishing PD, with its diagnostic power improving when combined with other motor abnormalities (hypokinesia, dysrhythmia, sequence effect). The likelihood of correctly identifying PD increased with the number of observed abnormalities, reaching up to 95% when all features were present. Levodopa improved motor performance, but the motor abnormality patterns remained unchanged. Conclusions: The detailed bradykinesia features assess- ment was crucial for differentiating PD individuals from controls. Diagnostic accuracy requires considering multi- ple motor abnormalities together, irrespective of the specific combination. Advancing our understanding of the ‘bradykinesia complex’ has clinical and patho- physiological implications.