Britta Siegmund

Background It is known that various chronic pain conditions lead to maladaptive changes in the central nervous system. Endometriosis is frequently associated with chronic pelvic pain (CPP). Its sufficient treatment remains a clinical challenge. Transcranial direct current stimulation (tDCS) has been shown to be a powerful method to reduce chronic pain. Therefore, this study aimed to investigate pain reduction via anodal tDCS in patients with endometriosis and CPP. Methods This clinical phase II, placebo-controlled, randomized, parallel-design study included 36 patients with endometriosis and CPP. All patients had CPP, defined as a score of ≥3/10 on the visual analog scale for ≥3 months in the prior 6 months. Anodal or placebo tDCS (18 patients per arm) was applied over the primary motor cortex for 10 days. The primary outcome measure was the pressure pain threshold (objective pain measure), and secondary outcomes were the numerical rating scale score (subjective pain measure), Von Frey monofilaments, and disease- and pain-related questionnaires. Data were collected at baseline, after the 10-day stimulation, and at a follow-up session, which took place 1 week after the tDCS had ended. Statistical analyses were performed with analyses of variance and t tests. Results Significant decreased pain perception in both pain measurements (pressure pain threshold and numerical rating scale score) was found for the active tDCS group compared with the placebo group. This proof-of-concept study shows that tDCS is a helpful supporting pain therapy for patients with endometriosis and CPP. Moreover, further analyses revealed that 1 week after the stimulation had ended, pain reduction as indexed by pressure pain threshold remained significantly decreased, which indicates possible long-term analgesic effects. Conclusion The present study provides evidence that tDCS is an effective therapy for pain reduction in endometriosis-associated CPP. The results support the notion that CPP is developed and maintained in the central nervous system, making a multimodal pain therapy necessary. Trial registration www.ClinicalTrials.gov ID: NCT05231239.