Electroencephalography Microstates Reveal Variability in Efficacy of Transcutaneous Auricular Vagus Nerve Stimulation in Primary Dysmenorrhea

Primary dysmenorrhea (PDM) is a prevalent gynecological disorder in young females, with limited treatment options despite its high prevalence and detrimental effects. Transcutaneous auricular vagus nerve stimulation (taVNS) has shown promise in alleviating PDM symptoms, but its long-term efficacy and individual variability remain uncertain. In this study, we utilized a single-blind, sham-controlled experimental design to investigate the long-term effects of taVNS on PDM. Sixty women with PDM were randomly assigned to receive either real or sham taVNS for 10 consecutive days, and 30 age-matched healthy controls were selected for baseline electroencephalography (EEG) comparison. The effects of taVNS were assessed at the first, second, and sixth menstrual periods post-treatment. Baseline resting-state EEG microstates were used to examine individual differences in taVNS efficacy. Our results demonstrated that taVNS effectively alleviates PDM symptoms, with benefits lasting at least 6 months. Additionally, menstrual pain may be associated with abnormal brain microstates related to saliency (class C) and the switching and reorientation of attention (class D). These neural alterations may mediate the relationship between baseline menstrual symptom severity and interindividual variability in taVNS efficacy. Our study highlights the effectiveness of taVNS for PDM treatment and underscores the importance of baseline microstates in influencing individual treatment responses.