Transcutaneous Electrical Nerve Stimulation for Endometriosis-related Chronic Pain

The study evaluates the effect of TENS (transcutaneous electrical nerve stimulation) as add-on treatment compared with conventional analgesic treatment in patients with endometriosis-related chronic pain. Patients with frequent pain and high pain intensity will be randomized to additional treatment with TENS or conventional treatment for 8 weeks to evaluate the acute effects of TENS treatment (n=40). Patients with endometriosis-related pain that is not frequent or without high pain intensity constitute an external control group. All patients in the study will receive TENS treatment for a total of 16 weeks, for evaluation of long-term effects of TENS treatment.

Endometriosis affects approximately one in ten women of childbearing age and may involve both acute pain related to the menstrual cycle and chronic pain. Usual analgesic therapy is often inadequate and/or involves unacceptable side effects and risks with long-term use. Transcutaneous electrical nerve stimulation (TENS) is a patient controlled treatment for pain relief with few side-effects. To date there is limited knowledge of how TENS treatment should be carried out for optimal pain relief in this patient group. The aim of the study is asses the effect of TENS as add-on treatment compared with conventional analgesic treatment in patients with endometriosis-related chronic pain. Patients with frequent pain and high pain intensity (≥ 4 according to Numeric Rating Scale, NRS) will be randomized to additional treatment with TENS or conventional treatment for 8 weeks in order to evaluate the acute effects of TENS treatment (n=40). Patients with endometriosis-related pain that is not frequent or without high pain intensity constitute an external control group. All patients in the study will receive TENS treatment for a total of 16 weeks, for evaluation of long-term effects of TENS treatment in chronic endometriosis-related pain. Prior to start of TENS treatment, all patients receive education on chronic endometriosis-related pain and TENS treatment. Study participants will be asked to participate in a qualitative follow-up within the study including a semi-structured individual interview (n=10-15) before intervention and a semi-structured focus group (n=9-15) interview after completion of TENS treatment.

Eligibility Criteria:
Inclusion Criteria:

* Age ≥18 years
* Consents to participation in the study
* Verified endometriosis (by laparoscopy or ultrasound).
* Chronic endometriosis-related pain (\> 3 months), available for TENS treatment
* Functioning, stable endometriosis-specific hormonal drug therapy. The endometriosis-specific drug therapy must be unchanged for the last 3 months and no gynecological surgical procedures for the treatment of endometriosis are planned during the next 7 months (during study participation). The endometriosis-specific drug therapy does not refer to analgesic therapy for symptom relief of endometriosis-related pain.

Exclusion Criteria:

* Patient with inability to understand and use written and spoken Swedish
* Patient with pacemaker and/or ICD or other electronic implants
* Patient with impaired sensation over the painful area
* Malignant disease with an expected survival \<12 months
* Alcohol or substance abuse
* Serious untreated psychiatric illness and/or psychological condition that is the primary determinant of the patient's condition
* Participating in another intervention study with possible impact on current study outcome measures
* Patient who is using \>90 morphine equivalents/day
* Patient who is electro-acupuncture
* Pregnancy