Objective: to characterize the therapeutic window of ring and directional stimulation in subjects with PD and DBS of the subthalamic nucleus (STN) or the Globus pallidus pars interna (Gpi).

Background: Deep brain stimulation (DBS) is an effective treatment for Parkinson Disease (PD) but can cause stimulation-related side effects. Conventional cylindrical DBS electrodes stimulate neurons all around the active contacts (i.e. ring stimulation), without the possibility of orienting the stimulation. This ring stimulation may affect untargeted brain regions activity, thus possibly causing motor and non-motor side effects. The directional DBS electrodes may now overcome this limitation by orienting the stimulation in horizontal directions.

Method: since April 2016, we implanted 15 PD patients with directional electrodes (13 STN-DBS and 2 GPi-DBS). One month after surgery, we performed an extensive programming session to characterize the efficacy and side-effect thresholds of both ring and directional stimulation. All patients were assessed after overnight suspension of all their dopaminergic medications (meds-off condition).

Results: Directional stimulation was selected in 53% of the patients. In particular, 5 subjects had directional stimulation in one of the two electrodes and 3 patients in both, whereas 7 patients benefited the most from conventional ring stimulation. In one example case, directional stimulation allowed the complete control of tremor and prevented the ring stimulation induced muscle contractions of the upper right limb.

Conclusion: The directional stimulation can enlarge the therapeutic window by increasing the threshold for stimulation-related side effects. This can improve the clinical outcome at the expenses of a longer and complicated programming. We described emblematic cases, detailing clinical and stimulation conditions in subjects with PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/directional-deep-brain-stimulation-whats-for/