What Is the Best Electrophysiologic Marker of the Outcome of Subthalamic Nucleus Stimulation in Parkinson Disease?

OBJECTIVE: Deep brain stimulation of the subthalamic nucleus (STN) is advocated in patients with advanced Parkinson disease. Intraoperative microelectrode recordings (MER) and stimulation or imaging are applied to confirm electrode targeting. The study objective was to evaluate which intraoperative electrophysiologic marker, MER, stimulation, or local field potentials (LFP) was the most predictive of the clinical efficacy.

METHODS: Efficacy was determined with lateralized motor scores of Movement Disorders Society-Unified Parkinson's Disease Rating Scale in 36 patients (OFF-drug/ON-stimulation 1 year after surgery vs. OFF-drug before surgery). Trajectory lengths in STN were determined from MER. Stimulation was increased up to the thresholds of first decrease, of complete suppression of rigidity, and of excitation of pyramidal motor tract. β oscillations (11-31 Hz) were computed from LFP of the electrode macrocontact. Univariate and multivariate analyses were computed.

RESULTS: Motor improvements were linked to trajectory lengths in STN (R2  = 0.17; P > 0.005). No significant relationship was found for thresholds of first decrease or suppression in rigidity or for motor tract excitation (R2 < 0.03, P > 0.05). Motor improvements were most linked to β oscillation increases (R2  = 0.57, P < 0.005, linear regression; R2  = 0.84, P < 0.0001, post hoc sigmoid regression). β oscillations appeared more predictive than length (β: t = 5.4, P < 0.001; length: t = 2.70, P < 0.03). Improvements were also slightly predicted by preoperative scores (R2  = 0.13; P < 0.005).

CONCLUSIONS: Motor improvements emerged as most related to β oscillations, before trajectory length within the STN, whereas stimulation thresholds of rigidity or of motor tract excitation failed to show any relationship. The study encourages LFP measurement to confirm STN electrode location.