Based on the pain threshold and visual simulation score, primary dysmenorrhea patients will be divided into treatment effective group or non-effective group.According to the functional magnetic resonance imaging, the investigators investigate whether there is characteristic or secondary brain features before and after rTMS intervention.

Long term primary dysmenorrhea may induce a series of disorders involving psychology, lower quality of life, or even developing chronic organic lesion or chronic pain. Effective symptom improvement is urgently needed. During the Non-pharmaceutical interventions, repetitive transcranial magnetic stimulation (rTMS) is received preliminary approval because of its noninvasive and safe analgesic effect. In this randomized single blind longitudinal study, the investigators investigate the analgesic effect of rTMS in long term moderate-to-severe primary dysmenorrhea women. Based on the pain threshold and visual simulation score, primary dysmenorrhea patients will be divided into treatment effective group or non-effective group. According to the functional magnetic resonance imaging, the investigators investigate whether there is characteristic or secondary brain features before and after rTMS intervention. By combining pre and post performances of the degree of dysmenorrhea, behavioral data and sensitive hematological indicators, the investigators intend to build an association model between brain and pain development curve. Using correlation and multiple regression analysis method, the investigators intend to find sensitive neuroimaging biomarkers in predicting the analgesic effect of rTMS. The current study is not only contributing to improve the central nervous systematic mechanism of rTMS in chronic pelvic pain, but also significant for clinical effective treatment based on neuroimaging predictive markers.

Inclusion Criteria:

• consistent with the diagnostic criteria for primary dysmenorrhea according to the American College of Obstetricians and Gynecologists;
• regular menstrual cycles (27-32 days);
• the average intensity of dysmenorrhoeic pain in the past 6 months should be rated ≥4 on a visual analogue scale (VAS) (0 = no pain, 10 = the worst imaginable pain).

Exclusion Criteria:

• organic pelvic disease;
• using oral contraceptives, hormonal supplements, Chinese traditional medicine or any central-acting medication (e.g., opioids, anti-epileptics) within 6 months before the study;
• comorbid chronic pain states;
• alcohol, nicotine or drug addiction;
• neurologic disease or psychiatric disorder;
• history of childbirth;
• a positive pregnancy test or immediate plans for pregnancy;
• any MRI contraindications. In addition, no analgesics were consumed 24 hours prior to the experiment.