Objective: To evaluate the safety and efficacy of unilateral subthalamic nucleus (STN) gamma knife surgery (GKS) in patients with Parkinson’s disease (PD) not amenable to deep brain stimulation (DBS).

Background: STN DBS has been shown to reliably improve several PD symptoms in appropriately selected patients. Various factors may preclude patients from undergoing DBS and for them, non-invasive lesion-based therapies such as focused ultrasound and GKS may present a safer alternative.

Method: Based on preliminary positive reports of STN GKS for PD, we conducted a prospective, open-label, single-center, pilot study in PD patients deemed potential candidates for unilateral DBS based on their disease characteristics, but contraindicated due to age>74, an irreversible bleeding diathesis, or significant comorbid medical disease. Stereotactic MRI-guided GKS was performed using a single 110 or 120 Gy dose targeting the STN contralateral to the more symptomatic extremity. Clinical follow up and imaging assessed the safety and efficacy of the procedure over a 12-month period.

Results: 4 PD patients with medication-refractory tremors and disabling dyskinesias underwent unilateral STN GKS. Contraindications to DBS included high risk comorbid cardiovascular disease in 3 patients and an irreversible bleeding diathesis in 1. There were no immediate post-procedural adverse events. 1 patient who underwent left STN GKS developed right hemiparesis and dysarthria 7 months post-procedure followed by hospitalization at 9 months for bacterial endocarditis and liver failure from which he died. The remaining 3 patients were free of adverse events up to 12 months post-procedure and experienced a statistically significant reduction in mean rigidity (-3.4, p < 0.01) and cumulative contralateral UPDRS-III scores (-8.4, p < 0.05). Upon extended follow up, 2 patients developed subacute worsening of gait. One died at 16 months due to complications of a fall whereas the other saw no change in gait up to 42 months post-procedure. All 3 patients with adverse events demonstrated a hyper-response in the targeted area on follow up neuroimaging.

Conclusion: Despite the potential for clinical improvement, our results suggest that unilateral STN GKS should be approached cautiously in medically frail PD patients who may be at higher risk of GKS hyper-response and neurologic complications.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/a-pilot-study-of-gamma-knife-radiosurgery-targeting-the-subthalamic-nucleus-in-elderly-and-infirmed-parkinsons-disease-patients-not-amenable-to-deep-brain-stimulation/