Objective: To evaluate the effect of unilateral STN-MRgFUS on ipsilateral motor symptoms at 6 and 12 months post-procedure.

Background: In patients with Parkinson’s disease (PD) and suboptimal motor control despite optimized therapy, several subthalamic-targeted interventions are available. Unilateral subthalamic deep brain stimulation and unilateral radiofrequency subthalamotomy have been reported to produce ipsilateral benefit [1-14], although this effect was mild and transient with the latter. With the increasing use of unilateral MRgFUS subthalamotomy (STN-MRgFUS), it remains unclear whether a comparable ipsilateral effect may occur [15-19].

Method: We analyzed PD patients treated with unilateral STN-MRgFUS at our center. Motor function was assessed using the MDS-UPDRS Part III at baseline and at 6 and 12 months. The primary outcome was the change in untreated-side motor score in the OFF-medication state. Secondary outcomes included untreated-side scores in the ON state, untreated hemibody subscores (rigidity, bradykinesia, and tremor), total and treated-side motor scores, Levodopa Equivalent Daily Dose (LEDD) [20], and safety at 12 months.

Results: A total of 39 patients were included. Baseline demographic, clinical and surgical characteristics are summarized in [Table 1]. No significant improvement was observed in untreated-side OFF MDS-UPDRS motor scores at 6 or 12 months (p = 1.00 for both comparisons), nor in subscores or ON motor scores [Table 2]. Significant improvement in total motor scores was driven by marked reductions in treated-side motor scores. LEDD was significantly reduced at both visits, and no disabling adverse events were reported at 12 months [Table 3].

Conclusion: Unilateral STN-MRgFUS did not provide ipsilateral motor benefit. Its therapeutic effect appears limited to the contralateral side, with significant and sustained improvement. Given the absence of ipsilateral benefit, some patients may require treatment of the opposite side over time, which should be clearly discussed during preoperative counseling [1,21].

Table 1. Baseline characteristics.

Table 2. Results (n=39).

Table 3. Adverse Events at 12 Months (n = 39).

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MDS Abstracts - https://www.mdsabstracts.org/abstract/does-unilateral-mr-guided-focused-ultrasound-subthalamotomy-provide-bilateral-motor-benefit-in-parkinson-disease/