TENS (transcutaneous electrical nerve stimulation) is accepted as a standard treatment for chronic pelvic pain, but the best settings to recommend, including frequency of stimulation, have not been defined to date. This study aims to find the optimal frequency, also known as cycles per second or Hertz (Hz) for treating chronic pelvic pain using non-invasive skin-level electrical nerve stimulation. The investigators will see how people respond to (20Hz, 50Hz or 100Hz). The study will have a two week control period (one week that looks back retrospectively at the week prior and another week looking prospectively at the patient symptoms) with no TENS unit and the participants normal standard of care treatments. This will be followed by 2 weeks of active TENS treatment for 30 minutes a day at the most painful time of day for the participant. The participant will also be allowed to extend their trial to study for durability for up to 3 additional months after the initial study. Participants will be asked to fill out a VAS (visual analog scale), GUPI (genitourinary pain index) and TENS usage log weekly.

Adults ages 18-90 years old who have first been given the standard of care therapy according to the AUA/EUA guidelines depending on their specific pain modality, first line treatments based on suspected etiology (for example pelvic floor physical therapy for high tone pelvic floor muscle dysfunction or amitriptyline for interstitial cystitis) without success will be defined as refractory. Participants who have plateaued on their response to current intervention strategies will be offered the TENS unit as an adjunct.

Participation will be offered by mail or in person. If by mail, the investigators will send the consent with the letter and questionnaires asking participants to call or bring the material if they would like to enroll. If the investigators speak to the subject over the phone, the investigators will discuss the study as comprehensively as if they were in the clinic. This will include explaining the concept of the TENS unit, the study itself, and clarifying any questions the participant has. Subsequently if they are interested in the study, the investigators will ask them to sign the consent and return it to us via mail or email.

Those whose pain symptomatology is above a threshold and who choose TENS therapy will be included in the study. The participants will be randomized into three groups of 25 participants each. The randomization will occur in blocks so that if the investigators need to terminate the study early there will be an equal number of participants in each group. The size of the blocks will also be kept secret for allocation concealment purposes. The randomization will be stratified by gender so that there is an equal number of participants from each gender in each group, reducing potential for gender as a confounding variable. Group 1 will be the low frequency set at 20 Hz. Group 2 will be the medium frequency set at 50 Hz. Group 3 will be the high frequency set 100 Hz. There is no sham group in this study as it has previously been found that posterior tibial TENS is effective and lasting. As such, all participants will be treated as a matter of routine medical care for pelvic pain. The investigators will use a fixed pulse width of 200 microseconds (uS), with continuous rather than biphasic stimulation. The investigators will aim to recruit 25 participants per group for a total of 75 participants.

Study Procedures

Screening Day 7/ Week 1 (in clinic or virtual): The first data points (Day 0) will take place in the clinic during the participant's routine visit or at the time of the participant's phone call seeking participation. If during a phone call seeking participation, this will be considered a study phone call, not a billable visit. The participant will fill out the VAS and GUPI. The participants will be taught how to fill out the pain assessment questionnaires (the VAS and GUPI, validated tools for measuring genitourinary pain and symptoms respectively). This can be done via paper to be brought into the office at their next checkup or via an emailed link through Qualtrics and uploaded to a spreadsheet in a protected AMC OneDrive. The baseline pain logs will be reviewed for sufficient severity of pain episodes and the participant will be randomized into the study if their pain is above the designated threshold: participants who record a pain scale of 4 or higher on any of the VAS scores or QOL score of 3 or higher on the GUPI question #9 will be eligible for the TENS study.

The GUPI and VAS will be collected at this time; this will record the participant's pain 1 week prior to the study and will be considered Day 7/week 1. The week 1 of screening will be combined with the first week of baseline measurement (week 2) for a 2-week lead-in. Participants will be taught how to complete a usage log (stating if the TENS was used each day and for how long in minutes) and will be asked to repeat this weekly. Participants will complete an inventory (the Treatment Map) of treatments tried prior to the TENS, throughout the study, and at the end.

Baseline Day 14/ Week 2: If the participant enrolls, they will be asked to continue logging pain (VAS and GUPI, on paper or via Qualtrics) for one week, with the week 1 screening and the week 2 baseline week totaling a 14-day control period. The control period will represent data (2 weeks of VAS and GUPI) with only baseline treatments and no TENS unit.

At week 2 (the end of the 2-week baseline, in person), participants will hand in scores and be randomized to a frequency. They will be given a TENS unit and taught how to use the unit. Teaching will include positioning of electrodes, as well as what buttons they are allowed to manipulate. The TENS unit settings will be pre-determined at the clinic and measures will be taken to ensure that the settings cannot be altered at home. The participant will be instructed not to open the TENS unit during the 2 treatment weeks of the study to ensure the settings are maintained. They will be instructed to continue only their baseline treatments.

Settings: The TENS unit used is a Compass Health TENS 3000, 3 mode Analog Unit. The participants' TENS unit will be set at Normal Mode (N), a pulse width of 200 microseconds and an intensity to be determined in the office based upon when the participant feels sensitive to the TENS unit. Frequency (pulse rate) will be determined by randomization. The participant will place the electrodes along the posterior tibial nerve on the medial ankle with a ground on the inner arch, each day for 30 minutes for a total of 14 days at the time of day typically associated with the worst pain or at the first opportunity for rest after this time.

Group 1 will be the low frequency group. This means that the TENS therapy will use a frequency of 20 Hz.

Group 2 will be the medium frequency group. This means that the TENS therapy will use a frequency of 50 Hz.

Group 3 will be the high frequency group. This means that the TENS therapy will use a frequency of 100 Hz.

Participants will be provided the TENS unit, its manual, and enough patches to last the 2 weeks of the treatment period. Participants will be given a weekly usage log, weekly pain VAS and weekly GUPI questionnaire logs again for 2 weeks they are actively using the TENS, with the option of paper or Qualtrics. In this log, the rating of pain by VAS and GUPI, the rating of genitourinary symptoms by GUPI, duration of TENS therapy, usage for every day of the week and adverse reactions to the TENS unit (rash) will be recorded.

Participants may be called during the 14-day treatment period to keep on track, address any concerns, questions, or any adverse reactions to TENS therapy by the physician or research staff. Their phone numbers will be maintained in the master key associated with the deidentified database in the AMC Onedrive protected research file for this purpose.

At 7 days and the end of the 14-day treatment period the visit can be performed either virtually or in the office. The 7-day visit will be considered purely a study visit and the 14 day visit a standard of care visit.

The completed week 3 and 4 VAS and GUPI, treatment usage documents will be returned. The participants will also be asked the question "Will you continue using TENS therapy for your pelvic pain?" Any persistent issues will be addressed during these visits as well and further options discussed.

For those who would like to continue the TENS unit, participants will be taught how to adjust settings and sites at home. Participants will be given repeat VAS and GUPI at 1, 2, and 3 months post-initial phase and seen again at 3 months as part of standard care. Here the investigators will review logs of what frequency patterns they developed with TENS usage on their own, if any. In this time participants may increase or decrease the frequency of their device anywhere in the range of 2 Hz to 150 Hz to see which they prefer most in this part of the trial. Participants will also be allowed to adjust pulse width (30 to 260 uS), mode (B N M), time (continuous, 15, 30 minutes), and intensity (1 to 8, 10-80mA) as desired. The only requests will be that they remove the device if any discomfort occurs and that they log their settings versus their response.

Inclusion Criteria:

1. Presenting with chronic pelvic pain (chronic/persistent pain that has been continuous or recurrent for at least three months (in accordance with EAU Guidelines).
2. Unsuccessful initial interventions based on initial assessments
3. Ability to provide informed consent and complete study requirements
4. Ability to complete a comprehensive history (including with an interpreter)

Exclusion Criteria:

1. Participants who have previously tried a new pharmacologic treatment for pelvic pain, neuromodulation or other alternative therapy for urologic disorders within the past 30 days
2. Inability to work a TENS unit
3. Any contraindications to usage of a TENS unit (pacemaker or other implantable device, lymphedema, pregnancy, malignancy, bleeding or clotting disorders, unhealthy tissue, seizure disorders, impaired cognition)
4. Any history of electrophysiologic heart disease or complications
5. Source of pain being an obvious anatomic issue requiring alternative treatment - for example urethral diverticulum, distal ureteric stone.
6. Participant who is pregnant
7. Participant with adhesive allergy either reported by the participant or upon chart review

There will be single blinding. Study participants/caretakers will not know which frequency has been assigned.