Evaluation of the Analgesic Effect of Intramyometrial Botulinum Toxin Injection Via Hysteroscopy in Pelvic Pain Suggestive of Dysmenorrhea

Inclusion Criteria: * Adult women who are not menopausal, * Presenting with: * Either severe primary dysmenorrhea, defined by an average pain intensity (VAS) ≥ 6/10 over the last 3 months at the inclusion visit, * Or, in cases of amenorrhea under hormonal treatment, severe chronic pelvic pain (average VAS ≥ 6/10 over the last 3 months), described as cramp-like, localized in the pelvic region, and similar to the initial dysmenorrhea pain. * Having failed optimal first-line medical treatment combining hormonal therapy and appropriate analgesics (Level I and II analgesics, and NSAIDs), * Having undergone a pelvic MRI within 1 year prior to the randomization visit that shows no evidence of deep infiltrating endometriosis or endometrioma, following systematic review by radiologists from the expert center managing the patient (if the pelvic MRI is deemed of insufficient quality for interpretation, a new MRI will be performed at the center), * Using a highly effective method of contraception (failure rate \<1%) for the entire duration of the follow-up period. Highly effective contraception methods are defined as one of the following: combined hormonal contraception (containing estrogen and progestin) with ovulation inhibition (oral, vaginal, or transdermal), progestin-only hormonal contraception with ovulation inhibition (oral, injectable, or implantable), intrauterine device (IUD), intrauterine hormonal system (IUS), condoms, bilateral tubal occlusion, vasectomized partner, or sexual abstinence, * Having a negative urine pregnancy test on the day of the procedure, * Having signed the informed consent form for the study at the M-1 visit. Exclusion Criteria: * Pregnant or planning a pregnancy during the entire study period, * Currently breastfeeding, * Refusal to use effective contraception during the study and for 6 months after its completion, * Contraindications to botulinum toxin, including: * Generalized disorders of muscular activity (e.g., myasthenia gravis, Lambert-Eaton syndrome), * Ongoing treatment with aminoglycosides, peripheral muscle relaxants, or amino-4-quinolines, * Hypersensitivity to the active substance, human albumin, or sucrose, * Bleeding disorders or current treatment with anticoagulants, * Ongoing vaginal or upper genital tract infection, * Participation in another interventional clinical trial, * Inability to cooperate or understand the study requirements in a way that would allow strict adherence to the protocol, * Subject to legal protection measures (e.g., guardianship, curatorship, or judicial protection), * Not affiliated with the French social security system, * Unable to access the internet to complete questionnaires at Month 1 and Month 6.