Subcutaneous Botulinum Toxin for Cutaneous Allodynia

Not Applicable

Completed

Brief Summary: 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).

Detailed Description: 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.

Recruitment & Eligibility

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

Arm && Interventions

Group	Intervention	Description
Placebo then Botox	Placebo - Saline	-
Botox then Placebo	Botulinum Toxin A	-

Primary Outcome Measures

Name	Time	Method
Time Until Analgesic Failure	Each participant was assessed for up to 224 days per intervention (injection) or until they returned to NRS baseline	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

Secondary Outcome Measures

Name	Time	Method
NRS Score Three Weeks After Injection	Three weeks after injection	The NRS scores range from 0-100, where 0 indicated no pain and 100 indicated the worst pain.