Transcutaneous Auricular Vagus Nerve Stimulation Added to Rehabilitation for Complex Regional Pain Syndrome Type I

Effectiveness of Transcutaneous Auricular Vagus Nerve Stimulation Added to Standard Rehabilitation in Patients With Complex Regional Pain Syndrome Type I: A Randomized Controlled Trial

This randomized, participant- and assessor-blinded, sham-controlled study will evaluate the effectiveness of transcutaneous auricular vagus nerve stimulation (taVNS) added to standard rehabilitation in adults with complex regional pain syndrome type I (CRPS-I) affecting the hand or upper extremity.

A total of 20 participants will be randomly assigned to two parallel groups. Both groups will receive the same standard rehabilitation program 5 days per week for 4 weeks. In addition, the experimental group will receive active taVNS, while the control group will receive sham taVNS for 30 minutes per session over the same 4-week period.

The primary outcome is change in pain intensity measured using the Numerical Rating Scale. Secondary outcomes include CRPS clinical severity, hand and wrist circumference, hand function and activities of daily living, health-related quality of life, anxiety and depression symptoms, and perceived stress. Assessments will be performed at baseline, at the end of treatment at week 4, and during follow-up at weeks 8 and 12.

Complex regional pain syndrome type I is a disabling condition that may develop after trauma, fracture, surgery, or immobilization. It is characterized by pain that is disproportionate to the initial injury and may be accompanied by sensory, autonomic, motor, edema, and trophic abnormalities. Despite multidisciplinary rehabilitation and pharmacological treatment, some patients continue to experience persistent pain and functional impairment.

Transcutaneous auricular vagus nerve stimulation is a non-invasive neuromodulation method that stimulates auricular regions innervated by the vagus nerve. It may affect pain processing, autonomic nervous system regulation, central sensitization, and neuroinflammatory mechanisms that may contribute to CRPS-I. Evidence regarding the clinical effectiveness of taVNS in this patient population remains limited.

The primary objective of this study is to determine whether active taVNS added to standard rehabilitation provides greater pain reduction than sham taVNS added to the same rehabilitation program. Secondary objectives are to compare the effects of the interventions on CRPS clinical severity, edema-related hand and wrist circumference measurements, hand function, activities of daily living, health-related quality of life, anxiety and depression symptoms, and perceived stress.

Participants will be randomly allocated in a 1:1 ratio to standard rehabilitation plus active taVNS or standard rehabilitation plus sham taVNS. Both groups will receive an identical 4-week rehabilitation program. Active and sham stimulation will be delivered with the same session duration and frequency. Participants and the outcomes assessor will be blinded to group allocation. The physiotherapist administering the stimulation will be aware of the allocation and will not participate in outcome assessments. Treatment effects and their persistence will be evaluated at weeks 4, 8, and 12.

Inclusion Criteria:

• Diagnosis of complex regional pain syndrome type I according to the Budapest diagnostic criteria
• Age 18 to 65 years
• CRPS type I affecting the hand following a traumatic cause, including surgery, fracture, and/or immobilization of the hand or upper extremity
• Willingness to participate in the study and provision of written informed consent

Exclusion Criteria:

• Diagnosis of complex regional pain syndrome type II
• CRPS type I developing after stroke
• Acute or post-acute rehabilitation following hand tendon repair
• Presence of a comorbid condition that may substantially affect functional status or health-related quality of life, including decompensated heart failure, chronic kidney failure, or malignancy
• Arthritis affecting the hand
• Acute arterial or venous thrombosis of the upper extremity
• History of arterial or venous injury of the upper extremity