Subcutaneous Botulinum Toxin for Cutaneous Allodynia

Superficial injection of Botulinum toxin has been advocated for cosmetic purposes but has also been reported to be helpful for some pain conditions. The investigators have observed prolonged profound analgesia following subcutaneous superficial injection of Botulinum Toxin Type A (BTA) in patients with certain types of neuropathic pain. The investigators propose to study if addition of BTA extends pain relief compared to placebo when injected subcutaneously into areas of cutaneous allodynia (the property that a normally non-noxious stimulus is perceived as painful).

Post-surgical neuromatous pain patients have marked cutaneous allodynia. Touching their skin with normally non-painful stimuli results in pain. Injected local anesthetics are often effective in providing temporary relief. In the course of clinical practice the investigators have observed that a number of patients with cutaneous allodynia have had marked persistent benefit from subcutaneous injection of Botulinum toxin Type A. Rather than killing targeted neurons, Botulinum toxin type A inhibits release of acetylcholine from cholinergic nerve terminals in a prolonged but ultimately reversible manner. Neuropathic pain and its hallmark allodynia are classically difficult to treat. Standard treatment with tricyclic antidepressants, anti-epileptic drugs, opiates and spinal cord stimulation is frequently disappointing leaving patients with refractory pain. Surgical or percutaneous ablation of involved nerves has fallen out of favor among many due to disappointing results. A pilot study is needed to assess the efficacy of superficially injected Botulinum Toxin type A for treatment of cutaneous allodynia and spontaneous pain among patients with neuropathic pain.

Participants made daily NRS reports via Palm Pilot, and "failure" was defined as (Pre-injection baseline NRS) - (Mean NRS for any 3 preceding days) ≤ 0; or 9 months

Each participant was assessed for up to 224 days per intervention (injection) or until they returned to NRS baseline

Inclusion Criteria:- Moderate to severe pain (greater than 4/10) of duration more than 6 months despite previous therapy. The patient exhibits at least 80% pain relief following injection of local anesthetic subcutaneously into scar as assessed by change in NRS The patient reports the presence of hyperalgesia, allodynia, dysesthesia, or hypoesthesia surrounding the scar Age 18-100 Ability to read, write, and converse in English, provide informed consent, and follow study procedures Exclusion Criteria: Any neuromuscular disorder such as myasthenia gravis, eaton lambert, muscular dystrophy Any ongoing legal action related to their pain Allergy to local anesthetics A current or history of any severe psychiatric disorder History of any adverse reaction to botulinum toxin History of botulism Untreated infection Coagulopathy Females - positive pregnancy test Surgery within the past 6 months at the site of the painful scar