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

Fibromyalgia (FM) is a chronic pain syndrome associated with widespread musculoskeletal pain, fatigue, sleep disturbances, and autonomic dysregulation. Current treatments provide only partial relief, highlighting the need for novel therapeutic approaches. Rationale: The vagus nerve is a key regulator of autonomic and inflammatory processes. Transcutaneous auricular vagus nerve stimulation (TaVNS) is a non-invasive technique that can modulate vagal activity through electrodes placed on the external ear, offering a potential alternative to surgically implanted vagus nerve stimulators. Study Design: This is a randomized, sham-controlled pilot trial conducted at Istanbul Medipol University. Thirty participants with fibromyalgia are randomized in a 1:1 ratio to receive either active TaVNS or sham stimulation. Intervention: Device: VagusStim® (Vagus Medical Technologies, Istanbul, Türkiye; CE-marked). Electrode placement: left cymba concha (active group) vs. left earlobe (sham group). Stimulation parameters: frequency 1-30 Hz, pulse width 50-250 μs, current intensity individually adjusted (0.1-36 mA) to each participant's sensory threshold. Schedule: 30 minutes per day, 5 days per week, for 4 consecutive weeks (20 sessions total). Supervision: All sessions are clinician-supervised. Outcome Measures: Primary outcomes: Pittsburgh Sleep Quality Index (PSQI) - subjective sleep quality. Fibromyalgia Impact Questionnaire (FIQ) - disease severity and functional impact. Central Sensitization Inventory (CSI) - symptoms related to central sensitization. Secondary outcomes: Visual Analog Scale (VAS) - pain intensity. Tampa Scale for Kinesiophobia (TSK) - fear of movement. Symptom Severity Scale (SSS). Widespread Pain Index (WPI). Assessment timepoints: baseline, week 2, week 4, and week 8.