The Effectivenes of Non-invasive Neuromodulation in Adult Women With Primary Dysmenorrhea, Through the TENS Stimulation at Different Times of Mentrual Cycle in Each Group

The effectiveness of non-invasive neuromodulation in adult women with primary dysmenorrhea, through the TENS stimulation at different times in each group: during the bleeding phase (G1), between days 25-28 and 1-3 of menstrual cycle, and in the luteal phase (GI2), between days 17 to 24 of menstrual cycle.

The control group (CG) will be treated just like GI1, during the bleeding phase, but without the TENS transmitting the current. Participants will be evaluated by the NPRS, MPQ, SF12, CVM-22, HADS, PCS, PSQI and UDP immediately after treatment in GI1 and GC, and at the beginning of the next bleeding phase, being 28 days after the intervention in the case of GI1 and GC, and 7 days after the intervention in the case of GI2, as well as 28 days after in this last.

This RCT evaluates women of legal age, with pain greater than 3 on the NPRS scale, and whose menstrual cycle is regular, considered regular between 25-30 days. The sample will be divided into a cases group which in turn will be divided into 2 subgroups: stimulation intervention in women with dysmenorrhea during the bleeding phase (GI1), and in the luteal phase (GI2). On the other hand, the control group (CG) will be treated just like GI1, during the bleeding phase, but without the transcutaneous electrical nerve stimulation (TENS) transmitting the current.

Initially, a screening questionnaire will be completed. Subsequently, a first assessment will be done to all included participants, which will be conducted by completing the Numerical Pain Scale (NPRS) in relation to their pain for 5 days, McGill Pain Questionnaire (MPQ), SF12 Health Survey, Specific Quality of life Questionnaire Related to Menstruation (CVM-22), Hospital Anxiety and Depression Scale (HADS) and Pain Catastrophizing Scale (PCS) and Pittsburgh Sleep Quality Index (PSQI), as well as pressure pain threshold measure (PPT). Participants will also be evaluated immediately after treatment and at the beginning of the next bleeding phase (next menstrual cycle), being 28 days after the intervention in the case of GI1 and GC, and 7 days after the intervention in the case of GI2.

Regarding the intervention, the treatment plan to be done will be as follows:

* GI1: TENS stimulation in the menstrual phase between days 25-28 (days before bleeding and where symptoms may begin) and 1-3 (first days of bleeding).
* GI2: TENS stimulation in the follicular phase between days 17 to 24 of the menstrual cycle after the start of bleeding.
* GC: Same procedure as GI1, but without TENS stimulation.

This intervention is performed using a TENS with an asymmetric biphasic wave of 200 µs width, frequency of 100Hz and maximum intensity tolerated by the participant, adapting to avoid accommodation. The intervention will be carried out for 30 minutes, once a day, and 2 days a week, with 48-72 hours between both interventions. Regarding the electrodes, 4 adhesive electrodes (5.0x5.0) will be placed, 2 in the lower lumbar region and two in the parasacral region (S2-S4).

Eligibility Criteria:
Inclusion criteria:

* Adult women
* Pain greater than 3 on the NPRS scale
* Women with regular menstrual cycle, considered regular between 25-30 days

Exclusion criteria:

* Pregnancy or breastfeeding
* Used of intrauterine device
* Diagnosed gynaecological pathology: endometriosis, polycystic ovaries, uterine fibroid, adenomyosis, fibrosis, uterine malformation, pelvic inflammation, scars, SDT...
* Skin lesions that prevent the placement of the electrodes
* Other diagnosed pathologies that contraindicate the application of TENS, neurological pathologies, or cardiovascular diseases
* Absence or doubling of bleeding in one month
* Taking analgesic medications and/or NSAIDs