Serratus Plane Block (SPB) Versus Capsaïcine Versus Botox-A for Chronic Neuropathic Pain in Post-mastectomy Syndrome

Inclusion Criteria :

1. Women aged ≥ 18 years;
2. Unilateral breast cancer treated by total or partial mastectomy:

   * with sentinel lymph node technique (SLN) or axillary dissection;
   * with or without immediate reconstruction using a prosthesis;
   * associated or not with radiotherapy and/or chemotherapy;
3. Presenting moderate to severe chronic neuropathic pain, defined by:

   * Numerical Pain Scale (NPS) ≥ 3 and DN4 ≥ 4,
   * on a localised aera ((≤ 240 cm²), at the surgical site, in the axillary hollow, or on the inner side of the ipsilateral arm,
   * between 3 and 9 months after breast surgery,
   * with indication of additional locoregional treatment in complement to a systemic treatment of chronic neuropathic pain, as recommended by the SFETD - French Society for the Study and Treatment of Pain (tricyclic antidepressants or IRSNA or gabapentinoid PLUS lidocaine patch, at the appropriate dosage) and implemented for at least 4 weeks;
4. Patient affiliated with a health insurance plan;
5. Patient informed and having consented to participate in the trial.

Exclusion Criteria :

1. Ipsilateral breast cancer recurrence, regardless of the first treatment;
2. History of breast or thoracic surgery prior to mastectomy with residual pain;
3. Painful polyneuropathy related to chemotherapy requiring treatment;
4. Ongoing or planned loco-regional adjuvant radiotherapy within the next 8 weeks;
5. Treatment area not suitable for potential botulinum toxin type A treatment;
6. Breast reconstruction using flap or lipomodelling;
7. Indication for breast reconstruction within the next 8 weeks;
8. Chronic pain of another etiology such as:

   * Neuropathic pain secondary to a neuroma (localized pain),
   * Radiodermatitis,
   * Phantom breast pain,
   * Lymphedema,
   * Complex regional pain syndrome,
   * Adhesive capsulitis,
   * Fibromyalgia;
9. Hypersensitivity or allergy to anesthetics, capsaicin, naropein, clonidine hydrochloride, an amide-type local anesthetic, botulinum toxin type A, or any excipient contained in the preparations;
10. Infection or inflammation at the injection site;
11. Therapeutic/effective anticoagulation;
12. Clinical signs or medical history leading to the diagnosis of:

    * Hemostasis disorder,
    * Local infection,
    * Severe renal insufficiency (creatinine clearance \< 30 mL/min),
    * Thrombocytopenia \< 50,000 platelets/mm3;
13. Generalized muscle activity disorders (e.g., myasthenia, Lambert-Eaton syndrome);
14. Heart rate lower than 60/minute;
15. Severe bradyarrhythmia due to sick sinus syndrome or second or third-degree atrioventricular block;
16. State of depression (HADS score ≥ 11);
17. Other contraindication to any of the study treatments;
18. Inability for the patient to follow the study schedule;
19. Inability for the patient or the healthcare team to perform the treatment within 2 weeks;
20. Pregnant or breastfeeding women, women who are able to conceive and who do not use a highly effective method of contraception during the trial and for at least 1 month after the end of treatment ;
21. Patient under guardianship or curatorship.