Design: Double-blind, randomized placebo-controlled trial.

Setting: Gynecology clinics at one academic institution.

Patients or Participants: To detect a 15 mm reduction in pain with 80% power and 0.05 significance level, 64 participants were required in each arm. Between December 2022 and December 2023, 135 participants undergoing an EMB were randomized: 68 in the active arm and 67 in the placebo arm. Baseline demographic and clinical characteristics were similar between groups.

Interventions: The FDA-approved TENS 7000 was used with pads placed parallel to the vertebral column at T10-L1/S2-S4 distribution and intensity was individually adjusted during EMB. The placebo arm did not receive stimulation due to an incomplete circuit.

Measurements and Main Results: The primary outcome was pain measured on a visual analog scale (0-100 mm) immediately after biopsy, with secondary outcomes including satisfaction and tolerability of TENS and pain scores at other timepoints. The median pain score after EMB was 50 mm (IQR 20-80) in active vs. 60 mm (IQR 40-100) in placebo TENS (p=0.039). Pain scores at other timepoints were not statistically significant. Overall satisfaction with pain control (100 mm representing completely satisfied) was 87.5 mm (IQR 60-100) in active vs. 70 mm (IQR 41-100) in placebo TENS (p=0.049); 85.3% of active TENS participants would use TENS in a future EMB. Minimal side effects were associated with TENS; one participant reported itching. In a subset analysis, participants with higher than median baseline anxiety had a difference in pain scores of 50 mm (IQR 40-80) in active vs. 80 mm (IQR 50-100) in placebo TENS.

Conclusion: There was a statistically but not clinically significant difference in pain between the active and placebo TENS groups after EMB, and satisfaction was higher in the active TENS group. Patients with higher baseline anxiety may benefit from TENS during EMB.