Expectation-driven modulation of subthalamic deep brain stimulation outcomes in Parkinsonian freezing of gait: a case report

Abstract

Background Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a treatment providing long-term efficacy for motor symptoms in Parkinson's disease (PD). However, the influence of patient expectations on freezing of gait (FOG), a complex and disabling axial symptom, has not been specifically reported. Methods A 64-year-old man with PD underwent bilateral STN-DBS for severe motor fluctuations and dyskinesias. STN-DBS electrodes were implanted under local anesthesia using MRI and electrophysiological targeting. After surgery, DBS programming was optimized and the motor symptoms, including FOG, were assessed clinically during DBS programming consultations. Results STN-DBS significantly improved motor symptoms, but several months post-surgery the patient developed recurrent and fluctuating FOG during ON stimulation. Notably, FOG improved not only after minimal stimulation adjustments (+0.1mA), but also after simulated changes based solely on verbal suggestion, without any objective modification of stimulation parameters. Conversely, simulated decreases in stimulation were associated with immediate worsening of gait. These observations were reproducible across multiple consultations. Conclusion This case suggests that FOG may represent a motor phenotype particularly sensitive to expectation, at the interface between neuromodulation and cognitive-affective processes. It supports a model in which STN-DBS establishes a permissive physiological state, while patient expectations and contextual cues influence the expression of locomotor function. Although these findings arise from a single-case observation, they highlight the potential impact of placebo and nocebo mechanisms on gait outcomes under STN-DBS and underscore the importance of considering non-specific effects during DBS programming and clinical follow-up.