Bicenter, randomized, parallel-group, double-blind, placebo-controlled study to evaluate the long-term efficacy and safety of botulinum toxin in two repeated administrations on pain related to mononeuropathy or polyneuropathy: Botnep Study

INTERVENTION: Trade Name: Botulinum toxin type A Product Name: Botox Pharmaceutical Form: Powder for injection* Pharmaceutical form of the placebo: Solution for injection Route of administration of the placebo: Intradermal use CONDITION: Painful peripheral neuropathies related to mononeuropathies (eg, traumatic, postherpetic...) or to polyneuropathies (eg, diabetic, idiopathic...) INCLUSION CRITERIA: 1/ Men or women, aged over 18 years and 85 years or younger. 2/ Presenting with spontaneous pain whose average intensity over the last 24 hours is greater than or equal to 4/10 on a 10-point numerical rating scale (concise pain questionnaire) 3/ Whose pain has been present for at least 6 months 4/ Presenting with "pure" or clearly predominant neuropathic pain (no other associated pain or negligible pain) 5/ Whose pain is related to a stable mononeuropathy or polyneuropathy (post-traumatic, post-surgical, post-herpetic neuralgia, mononeuritis in the context of a stabilized systemic disease, diabetic polyneuropathy, idiopathic, systemic disease) confirmed by clinical examination and/or appropriate electrophysiological examination (EMG) 6/ Having a good command of the French language and being able to understand the study methodology and questionnaires 7/ Having given their consent PRIMARY OUTCOME: Main Objective: - To evaluate The benefit of repeated administrations of botulinum toxin type A at 3 to 6 month intervals compared to placebo (physiological saline) in patients with peripheral neuropathic pain (mononeuropathy, polyneuropathy) in order to assess the clinical benefit of the product in this indication; - To evaluate the mechanisms of action of botulinum toxin by quantifying its impact at 1 month on the neuropeptides CGRP, SP and the vanilloid receptor TRPV1 of peripheral fibers, presumed targets of action of BTX-A, from skin biopsies obtained in painful areas; Primary end point(s): Self-assessment scale of the weekly averages of pain scores reported by the patient in their self-assessment diary throughout the study. The patient will assess their pain over the past 24 hours every day at the same time (in the morning) using a 10-point Likert scale (from 0: no pain to 10: worst pain imaginable). A patient will be considered compliant and the assessment adequate if the diary is completed at least 4 days out of 7 (see exclusion criteria). Secondary Objectives: - To evaluate the proportion of patients responding to BTX-A; - To evaluate the efficacy of botulinum toxin on painful symptoms; - To evaluate the time to achieve a therapeutic effect on spontaneous pain; - To evaluate the proportion of patients requiring a second administration of BTX-A; - To evaluate the average duration of effect of each BTX-A administration; - To evaluate the potential additional benefit of a second BTX-A administration. - Evaluate the effect of BTX-A on the intensity and area of ​​allodynia upon friction; - Evaluate the impact on quality of life and sleep; - Evaluate the safety and tolerability of the treatment; - Evaluate any differences in response between the group with mononeuropathy and the group with polyneuropathy; - Investigate predictive factors of therapeutic response.