Laterality-dependent biological effects of manual acupuncture stimulation of the auricular vagus nerve in women with fibromyalgia: a randomized, sham-controlled trial.

BACKGROUND

Auricular vagus nerve stimulation (aVNS) has emerged as a noninvasive neuromodulatory strategy with the potential to modulate central sensitization and inflammatory pathways. However, its role in fibromyalgia (FM) remains insufficiently explored.

OBJECTIVE

To investigate whether stimulation laterality (left vs right auricular branch of the vagus nerve) differentially influences clinical and biological outcomes in women with FM.

METHODS

In this randomized, double-blind, sham-controlled trial, 51 women with FM were allocated to sham stimulation, right-sided aVNS (aVNS-R), or left-sided aVNS (aVNS-L). Participants underwent weekly sessions for 4 weeks and were followed for 12 weeks. Pain intensity was the primary outcome. Secondary outcomes included psychological symptoms, sleep, functional status, quality of life, and circulating biomarkers (pro- and anti-inflammatory cytokines, brain-derived neurotrophic factor [BDNF]).

RESULTS

While no significant between-group differences were observed in pain intensity, left-sided stimulation (aVNS-L) was associated with a modest but significant reduction in global symptom severity. Importantly, aVNS-L produced consistent immunomodulatory effects, including decreased IL-1β and TNF-α levels, and increased IL-4, IL-10, and BDNF concentrations.

CONCLUSIONS

This exploratory trial suggests that stimulation laterality may shape the biological response to aVNS in FM. Although clinical pain relief was not superior to sham, left-sided stimulation promoted an anti-inflammatory profile and enhanced neuroplasticity markers. These findings support further investigation of aVNS laterality as a targeted neuromodulatory approach for FM.

TRIAL REGISTRATION: Brazilian Clinical Trials Registry RBR-10d3crcf.