Optimization of Deep Brain Stimulation Surgery for Parkinson Disease with Quantitative Rigidity Evaluation

Aim: Deep brain stimulation (DBS) is an established treatment of movement disorders such as Parkinson disease (PD). The aim of this study was to optimize target selection by quantitatively evaluating rigidity during DBS surgery. Method: Effective DBS requires a well-positioned electrode. To optimize electrode targeting, test stimulation is performed during DBS surgery: an examiner observes the effect on symptoms for each position of the test electrode. The neurologist evaluates the effect on rigidity by passively moving the patient's arm or hand about a joint and determining, for each electrode position, the amplitude of stimulation that alleviates rigidity to the greatest extent (best clinical amplitude, BCA). In this study, we evaluated rigidity quantitatively with accelerometry, assuming that reduced rigidity would be reflected by an increased speed of passive movement. Data from an acceleration sensor mounted on the neurologist's wrist were recorded in a synchronized manner. A baseline evaluation was performed without stimulation. The data were analyzed postoperatively to quantify changes in rigidity and to identify the stimulation amplitude at which rigidity was maximally alleviated (best quantitative amplitude, BQA). BCA and BQA were statistically compared. Moreover, for every stimulation position, the surgical team postoperatively identified the anatomical site of the center of the stimulating contact. We used this information to group the datasets into brain structures and then compared the quantitative findings across structures. 141 test stimulations were performed in 9 PD patients participating in a clinical study at the University Hospital in Clermont-Ferrand. The stimulation sites were grouped into 3 structures: the subthalamic nucleus (STN), the zona incerta (ZI), and the field of Forel (FF). Results: The mean BQA (0.95 ± 0.68 mA) was significantly lower (p < 0.001) than the mean BCA (1.40 ± 0.60 mA). In other words, accelerometric analysis detected maximal effects on rigidity at lower stimulation amplitudes than clinical testing did. Of the three brain structures tested, the STN had the lowest BCA and BQA values. Conclusion: Quantitative rigidity evaluation in DBS surgery may improve intraoperative localization of the optimal DBS target site. Better targeting could lower effective stimulation amplitudes, reduce side effects, and prolong battery life. Our findings also confirm that the STN is the most effective DBS target for lessening rigidity.

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