Analyzing the 'Bradykinesia Complex' in Parkinson's Disease.

BACKGROUND Bradykinesia is the hallmark sign of parkinsonism. We recently proposed redefining bradykinesia as a complex of motor abnormalities, 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 analysis 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 features 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 amplitude as well as altered rhythm and sequence effect compared 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 assessment was crucial for differentiating PD individuals from controls. Diagnostic accuracy requires considering multiple motor abnormalities together, irrespective of the specific combination. Advancing our understanding of the 'bradykinesia complex' has clinical and pathophysiological implications. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.