Chronic pelvic pain (CPP) syndrome is characterized by a nonmalignant perceived pain in pelvic structures [1]. Common pharmacological and surgical treatments were often reported as unsatisfactory in patients with CPP [2]. Transcutaneous electrical
nerve stimulation (TENS) is considered to be a common noninvasive peripheral neuromodulation and affordable method to manage pain and guard muscles [3].
This study aimed to identify the effects of TENS in women with CPP by conducting a systematic review and meta-analysis of randomized controlled trials.

We performed a systematic search of five electronic databases, including PubMed, Science Direct, Embase, Cochrane, and Scopus, from 2000 to 2020 and selected the clinical trials that reported the effects of TENS on CPP. The case reports, acute pelvic pain reports, men-related, animal-related, and intravaginal and intrarectal electrical stimulation articles were excluded. The level of pain (based on the visual analog scale) was considered for pooling data through the meta-analysis.

Ten studies met the inclusion criteria, and three articles were included in the meta-analysis. The results showed that TENS application mildly reduced pain in women with CPP (mean difference = −1.29; 95% CI: −2.57 to −0.01; Z = 1.98, p = 0.05). Also, to reduce pain for these patients, the TENS must be applied for at least 20 min, with a pulse duration of 50–400 μs, at a frequency of 2–120 Hz. The meta-analysis was followed by assessing the risk of bias, including publication bias. Based on the Cochrane risk of bias evaluation, the majority of the included trials were assessed with moderate methodological quality.

Overall, most of the researchers found that TENS was more effective in pain relief compared with the placebo and/or control groups in patients with CPP. In general, different types of TENS have been used to decrease the level of pain in patients with CPP. The reported mechanism of pain reduction following the high-frequency TENS application differs from those of the low-frequency TENS. High-frequency TENS might transmit stronger afferent inputs to the central nervous system and lead to stronger segmental inhibition in nociceptive transmitters from second-order neurons.

TENS application can mildly improve the level of pain in patients with CPP. Although no distinct agreement was observed among the effective parameters, the high-frequency mode with maximum tolerated intensity was more effective compared to the low-frequency mode. Further investigations with well-designed studies and placebo groups are necessary to suggest more effective TENS parameters that would help reach better improvement in patients with CPP.

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