Effect of Transcutaneous Auricular Vagus Nerve Stimulation on Conditioned Pain Modulation in Trigeminal Neuralgia Patients

Introduction: Conditioned pain modulation (CPM) is a quantitative estimation of the capacity for endogenous pain modulation. Reduced CPM enables chronic painful event development or exacerbates pre-existing pain symptoms. Emerging reports indicate that patients with trigeminal neuralgia (TN) have dysregulated endogenous pain modulation. Transauricular vagus nerve stimulation (taVNS) is known to alleviate both acute and chronic pain symptoms. Its role in modulation or management of TN remains unknown. Here, we evaluated the taVNS efficacy in modulating CPM among TN patients. Conclusions from this investigation may facilitate establishment of novel non-invasive adjunctive approaches to treating TN patients. Methods: All research work was conducted at the First Affiliated Hospital of the University of Science and Technology of China (Anhui Provincial Hospital). In all, we recruited 62 study participants, 31 TN patients and 31 healthy volunteers, for a 2-day experimental test. At the beginning of the experiment (Day 1), all subjects received 30 min of active taVNS. On Day 2, they received sham taVNS with the same duration and intensity. Meanwhile, technicians documented participant pressure pain thresholds (PPT) and CPM values at baseline, and at 15 and 30 min post-active or sham taVNS. Results: A 30-min active taVNS exposure substantially elevated the PPT and CPM effect (P < 0.05) among TN patients, and we also observed a notable rise in the PPT and CPM effect (P < 0.05) among healthy controls. Additionally, there were no serious adverse events from the administered treatment. Conclusion: Exposure to 30 min of active taVNS strongly augmented the CPM effect and elevated the PPT among TN patients and healthy controls. These effects were not observed with sham stimulation. Despite the limitations inherent to survey studies, such as duration and compliance biases, we consider that taVNS is a promising, safe, and cost-effective therapy. In future investigations, we recommend assessment of long-term taVNS application and its effects on CPM and clinical pain.