Are quantitative and clinical measures of bradykinesia related in advanced Parkinson's disease?

Introduction: Bradykinesia is usually assessed using clinical rating scales. In some circumstances, a laboratory assessment of bradykinesia using tools of higher resolution is required. One task often used for the evaluation of bradykinesia is a rapid alternating movement (RAM) of the hand. However, the relationship between clinical scores of bradykinesia and the properties of a RAM task assessed quantitatively has yet to be determined. Objective: Identify which of the commonly used properties of a RAM task are related to a clinical score of bradykinesia and assess the strength of this relationship. Methods: Nineteen patients with idiopathic Parkinson's disease were tested ON and OFF medication. They performed three trials of the RAM task and were assessed clinically using the Unified Parkinson's disease rating scale in each condition and with each hand. Results: A statistically significant correlation was observed between the clinical score of bradykinesia and two of the properties of the RAM task; namely mean and maximal velocity. Comparison with existing methods: These results indicate that a RAM task does provide a measure of bradykinesia but it is only moderately correlated to a clinical rating of this motor symptom. Conclusion: We propose that the results from the RAM task represent a measure of "core bradykinesia" while a clinical evaluation represents a composite score of bradykinesia, movement amplitude and motor coordination.