What is the role of botulinum toxin (BTX) injections in the management of neuropathic pain?

Updated: Jun 19, 2018
  • Author: Anthony H Wheeler, MD; Chief Editor: Meda Raghavendra (Raghu), MD  more...
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BTX is effective in the management of neuropathic pain, which is caused by damage or dysfunction within the central or peripheral nervous system. Conditions such as postherpetic neuralgia (PHN), spinal radiculopathy, complex regional pain syndrome (CRPS), spinal cord injury, and brachial plexus injury are examples of neuropathic pain syndromes. [73] BTX-A has demonstrated relief of pain in conditions associated with muscular overactivity, but may also be effective in the treatment of neuropathic pain. Multiple neurochemical and neurophysiological mechanisms have been cited that could explain potential actions of BTX-A as a therapeutic agent for neuropathic pain.

Freund and Schwartz reported reduced pain in 7 patients with trigeminal, thoracic, or lumbar PHN of more than 6 months who were treated with subdermal BTX-A injections at a concentration of 5 U per 0.1 cc preservative-free normal saline into every 9 cm3. [74] In another report, 2 patients with cervical spinal cord lesions experienced hyperesthesia, allodynia and burning pain in a segmental dermatomal distribution. [75] Patients were treated with multiple point subcutaneous injections of BTX-A in the involved dermatome. Definite analgesia was obtained and then maintained by repeating injection treatments every 4-6 months. Injections in one patient were discontinued at 3 years and in the second patient after 2 years, when neuropathic pain symptoms subsided.

A series of 3 case reports included treatment of chronic refractory neuropathic pain in 2 patients with PHN and another with an S1 radiculopathy. [73]

A physician with PHN of the left V-1 region was treated with BTX-A and rapidly experienced complete pain relief except for an area of pruritus with intermittent paroxysmal pains in the medial canthus area. This area was reinjected with 5 U of BTX-A, and paroxysmal pain resolved. At 2 years and over 5 years following his initial injection session, the patient reported occasional mild pruritus in the left V1 area when "overheated or stressed."

The second patient had right lateral foot pain and allodynia in an S1 pattern due to PHN. He chose to try BTX-A following multiple oral and topical medication therapies. The patient received incomplete relief in the anterior two-thirds of the affected area, but minimal relief in the posterior third of the affected area despite reinjection. At 4 months follow-up pain recurred, and he chose not to repeat BTX-A treatment.

The third case was a male attorney with an 8-year history of right S1 radicular burning, with pain and allodynia affecting the right lateral foot. Extensive diagnostic workup was negative and pharmacological/nonpharmacological therapies were ineffective. Selective nerve root blocks demonstrated a painful S1 radiculopathy without any structural cause amenable to surgical therapy. Subsequently, BTX-A injections caused complete resolution of S1 burning pain and allodynia, which had continued beyond 18 months and now beyond 10 years follow-up.

Injection techniques for these patients were similarly from a technical standpoint to those with hyperhidrosis. The affected sensory area was outlined, then divided into grids between 1.25 – 1.50 cm squares or diameter circles. BTX-A dosage and dilution was determined by the thickness and resistance of the skin region to be injected and grid-size.

Long-lasting analgesia of neuropathic pain was demonstrated in 2 experimental studies using rats with either alloxan or streptozotocin-induced diabetic peripheral neuropathy. A single subcutaneous injection of BTX-A produced a prolonged antinociceptive effect as measured by mechanical sensitivity/ [76, 77]

An abstract by Relja and Militec presents a prospective study of BTX-A treatment of painful diabetic neuropathy, whereby 41 symptomatic patients were randomized into a BTX-A 100 U treatment or placebo group. [78] Injection methodology was not discussed in the published abstract. All patients completed the study. Significant improvements were noted in all outcome measures, including the endpoint mean pain score, VAS, global assessments, and the SF–36 Questionnaire.

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