Botulinum Toxin in Peripheral Neuropathic Pain

Pain due to peripheral nerve lesion remains extremely difficult to treat and current treatments have onl moderate efficacy and/or side effects. The investigators have previously demonstrated the long term efficacy of Botulinum toxin type A (BTX-A) in a small group of patients with post-traumatic/postherpetic neuralgia and allodynia. The present study aims to a/ confirm the efficacy of repeated applications of BTX-A in a larger group of patients with peripheral neuropathic pain with or without allodynia(primary outcome) ; b/ evaluate its mechanisms of action ; c/analyse the predictors of response ;d/analyse whether the second injection is associated with a therapeutic gain. This will be a randomized placebo controlled study. A total of 30 patients will be randomized to receive either BTX-A (subcutaneous injection in the painful area) or placebo. Each injection will be repeated within at least 3 months depending on the duration of efficacy. Skin punch biopsies will be performed before and 1 month after BTX-A administration. The investigators postulate that this study will confirm the clinical efficacy and good safety of repeated administrations of BTX-A in the treatment of peripheral neuropathic pain.