Botulinum toxin for chronic pain: What's on the horizon?
Botulinum toxin has proven safe and effective when used correctly. This review examines the evidence that could support its expanded use.
PRACTICE RECOMMENDATIONS
› Consider botulinum toxin (BoNT) for patients with headache, spasticity, or cervical dystonia, as the FDA has approved BoNT for pain relief in these conditions. A
Strength of recommendation (SOR)
A Good-quality patient-oriented evidence
B Inconsistent or limited-quality patient-oriented evidence
C Consensus, usual practice, opinion, disease-oriented evidence, case series
Chronic exertional compartment syndrome
Chronic exertional compartment syndrome (CECS) is defined subjectively as pain in a specific compartment that develops during exercise and resolves upon stopping, as well as objectively with an increase in intra-muscular pressure.22 It is most common in the lower leg and is a difficult condition to manage. Nonsurgical and surgical options are only successful at returning the patient to full activity 40% to 80% of the time.23
An initial study done in 2013 of BoNT injected into the anterior and lateral compartments of the lower extremity showed that symptoms resolved completely in 94% of patients treated.22 The actual mechanism of benefit is not clearly understood but is potentially related to muscle atrophy and loss of contractile tissue. However, it has not been reported that these changes have affected the strength or performance of patients who receive BoNT for CECS.23
Thoracic outlet syndrome
Thoracic outlet syndrome (TOS) is a compression of neurovascular structures within the thoracic outlet. There are several locations of potential compression, as well as possible neurogenic, vascular, or nonspecific manifestations.24 Compression can be from a structural variant, such as a cervical rib, or due to soft tissue from the scalene or pectoralis musculature. TOS is difficult to diagnose and treat. Physical therapy is the mainstay of treatment, but failure is common and treatment options are otherwise limited. Decompression surgery is an option if conservative management fails, but it has a high recurrence rate.24
In an effort to harness the therapeutic value of muscle atrophy, denervation, and relaxation afforded by BoNT, clinicians have injected the agent into the anterior and middle scalenes and the pectoralis minor to provide patients with relief from TOS.24 This treatment requires advanced imaging with either fluoroscopy or ultrasound guidance for correct placement and knowledge of surrounding anatomy. Small case reports and case series have demonstrated success, but a small double-blind randomized controlled study of 37 individuals with neurogenic TOS in 2011 did not show a reduction in symptoms.25 Multiple subsequent case reports and case series have continued to show positive results.24,25 A recent retrospective study showed that patients with TOS who had positive results with BoNT had better surgical outcomes.26
Trigeminal neuralgia and peripheral nerve pain
A meta-analysis in 2019 reviewed evidence for trigeminal neuralgia as well as other types of peripheral neuropathies, including diabetic neuropathy and postherpetic neuropathy. It showed that BoNT injections are safe, as well as effective, for short-term relief at 3 months. However, overall study sizes were small and long-term data are still lacking; larger high-quality studies are needed for further substantiation.27
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