Effects of Transcutaneous Auricular Vagus Nerve Stimulation on Symptom Severity, Sleep Quality, Central Sensitization, and Kinesiophobia in Fibromyalgia

Active TaVNS delivered with the VagusStim® device (Vagus Medical Technologies, Istanbul, Türkiye). The bipolar electrode was placed on the left cymba concha. Stimulation was applied for 30 minutes per day, 5 days per week, for 4 weeks (20 sessions). Parameters included frequency 1-30 Hz, pulse width 50-250 μs, and current intensity individually adjusted (0.1-36 mA) to the participant's sensory threshold.

Sham stimulation delivered with the same VagusStim® device under identical conditions. The electrode was rotated and placed on the left earlobe, which lacks vagal innervation. Sessions lasted 30 minutes per day, 5 days per week, for 4 weeks (20 sessions). No effective vagus nerve stimulation was delivered, preserving participant blinding.