Botulinum toxin treatment of pain syndromes -an evidence based review

Botulinum Toxin and Pain

This chapter is focused on analgesic mechanism of action of botulinum toxin type A (BoNT-A) including the action beyond peripheral nerve endings. With the exception of the meninges and possibly urinary bladder, the presence of BoNT-A activity in the periphery, cleaving SNAP25 as a target molecule, up to now was not convincingly shown. In contrast many reports demonstrated BoNT-A activity and the presence of cleaved SNAP25 in the brain and spinal cord. In a model of mirror pain BoNT-A analgesic effect can be achieved even without participation of peripheral nerve ending. Thus generalized hypothesis central or peripheral mechanism of action belongs to history, and there is a need to confirm or dispute the results with meninges, urinary bladder, and possibly with other, especially visceral organs.There are two general options for the central actions of BoNT-A: 1. The activity ends by silencing primary sensory neuron thereby stopping the pain information further in the CNS. 2. Or thereafter, indirectly or transsynaptically, BoNT-A triggers smaller or larger neural loops, forming memory of pain in the CNS that could explain the bilateral effects after unilateral peripheral administration, similar effect in mirror image allodynia and the like Intensive research has shown that peripherally administered BoNT-A reaches the CNS by axonal transport. There is increasing evidence that BoNT-A is preventing pain in a growing range of disorders. In the absence of unexpected findings, or an increase in the uncontrolled use of illicit preparations by uneducated persons, BoNT-A is emerging as a new long-lasting and relatively safe analgesic.

Botulinum Toxin Type A in Dental Medicine

Botulinum toxins (BoNTs) are a product of the bacteria Clostridium botulinum. By entering nerve endings, they cleave and inactivate SNARE proteins, which are essential for neurotransmitter release. Prevention of acetylcholine release at the neuromuscular junction causes long-lasting and potentially fatal flaccid paralysis-a major feature of botulism. However, an intramuscular injection of minute amounts of BoNTs, primarily type A (BoNT-A), has useful long-lasting muscle relaxation effects on spastic motor disorders. This characteristic of BoNT-A is widely used in neurology and cosmetics. Over the last few decades, it has been demonstrated that the functions of BoNT-A are not limited to muscle-relaxing or autonomic cholinergic effects but that it can act as an analgesic agent as well. More recently, it was revealed that this antinociceptive effect starts after entering the sensory nerve endings, where these agents are axonally transported to the central nervous system, suggesting that at least part of their analgesic effect might be of central origin. Because of its antinociceptive effect, BoNT-A is currently approved for treatment of chronic migraine; nonetheless, case reports and preclinical and clinical experiments indicating its benefit in numerous potential painful conditions have increased. In the field of dentistry, the US Food and Drug Administration approved BoNT-A for the treatment of sialorrhea only. Legal status of the use of BoNT-A in other countries is less known. However, there are controlled clinical trials suggesting its efficacy in other conditions, such as bruxism, temporomandibular disorders, and trigeminal neuropathic pain. Thereby, using criteria of the American Academy of Neurology, we critically reviewed the uses of BoNTs in oral medicine and found it effective for trigeminal neuralgia (category A) and probably effective in temporomandibular disorders and bruxism.

Treatment of at-level spinal cord injury pain with botulinum toxin A

Study design

Randomized, double-blinded, placebo-controlled, cross-over study.

Objective

To explore whether botulinum toxin A (BoNTA) could be effective for treating at-level spinal cord injury (SCI) pain.

Setting

Outpatient SCI clinic, New York, USA.

Methods

Participants were randomized to receive subcutaneous injections of either placebo or BoNTA with follow-up (office visit, telephone, or e-mail) at 2, 4, 8, and 12 weeks to assess the magnitude of pain relief post injection. Crossover of participants was then performed. Those who received placebo received BoNTA, and vice versa, with follow-up at 2, 4, 8, and 12 weeks.

Results

Eight participants completed at least one of the two crossover study arms. Four completed both arms. The median age of the eight participants was 45 years (range 32-61 years) and 75% were male. All had traumatic, T1-L3 level, complete SCI. Although our data did not meet statistical significance, we noted a higher proportion of participants reporting a marked change in average pain intensity from baseline to 8 and 12 weeks post-BoNTA vs. post-placebo (33% vs. 0%). At 2 and 4 weeks post-BoNTA, almost all participants reported some degree of reduced pain, while the same was not seen post-placebo (83% vs. 0%).

Conclusion

The subcutaneous injection of BoNTA may be a feasible approach for the control of at-level SCI pain and is worthy of further study.

Sponsorship

The onabotulinumtoxinA (BOTOX) used in this study was provided by Allergan (Irvine, CA).

Mechanisms of Botulinum Toxin Type A Action on Pain

Already a well-established treatment for different autonomic and movement disorders, the use of botulinum toxin type A (BoNT/A) in pain conditions is now continuously expanding. Currently, the only approved use of BoNT/A in relation to pain is the treatment of chronic migraines. However, controlled clinical studies show promising results in neuropathic and other chronic pain disorders. In comparison with other conventional and non-conventional analgesic drugs, the greatest advantages of BoNT/A use are its sustained effect after a single application and its safety. Its efficacy in certain therapy-resistant pain conditions is of special importance. Novel results in recent years has led to a better understanding of its actions, although further experimental and clinical research is warranted. Here, we summarize the effects contributing to these advantageous properties of BoNT/A in pain therapy, specific actions along the nociceptive pathway, consequences of its central activities, the molecular mechanisms of actions in neurons, and general pharmacokinetic parameters.

Botulinum Toxin in the Management of Children with Cerebral Palsy

During the past 25 years, botulinum toxin type A (BoNT-A) has become the most widely used medical intervention in children with cerebral palsy. In this review we consider the gaps in our knowledge in the use of BoNT-A and reasons why muscle morphology and function in children with cerebral palsy are impaired. We review limitations in our knowledge regarding the mechanisms underlying the development of contractures and the difficulty in preventing them. It is clear from this review that injection of BoNT-A in the large muscles of both the upper and lower limbs of children with cerebral palsy will result in a predictable decrease in muscle activity, which is usually reported as a reduction in spasticity, for between 3 and 6 months. These changes are noted by the use of clinical tools such as the Modified Ashworth Scale and the Modified Tardieu Scale. Decreased muscle over-activity usually results in improved range of motion in distal joints. Injection of the gastrocnemius muscle for toe-walking in a child with hemiplegia or diplegia usually has the effect of increasing the passive range of dorsiflexion at the ankle. In our review, we found that this may result in a measurable improvement in gait by the use of observational gait scales or gait analysis, in some children. However, improvements in gait function are not always achieved and are small in magnitude and short lived. We found that some of the differences in outcomes in clinical trials may relate to the use of adjunctive interventions such as serial casting, orthoses, night splints and intensive therapy. We note that the majority of clinical trials of the use of BoNT-A in children with cerebral palsy have focussed on a single injection cycle and this is insufficient to understand the balance between benefit and harm. Most outcomes were reported in terms of changes in muscle tone and there were fewer studies with robust methodology that reported improvements in function. Changes in the domains of activities and participation have rarely been reported in studies to date. There were no clinical reviews to date that consider the findings of studies in human volunteers and in experimental animals and their relevance to clinical protocols. In this review we found that studies in human volunteers and in experimental animals show muscle atrophy after an injection of BoNT-A for at least 12 months. Muscle atrophy was accompanied by loss of contractile elements in muscle and replacement with fat and connective tissue. It is not currently known if these changes, mediated at a molecular level, are reversible. We conclude that there is a need to revise clinical protocols by using BoNT-A more thoughtfully, less frequently and with greatly enhanced monitoring of the effects on injected muscle for both short-term and long-term benefits and harms.

Pharmacotherapeutic options for complex regional pain syndrome

INTRODUCTION

Complex regional pain syndromes (CRPS) are rare painful conditions characterized by considerable variability in possible triggering factors, usually traumatic, and in the clinical scenario. The limited knowledge of the pathophysiological mechanisms has led to countless treatment attempts with multiple conservative and surgical options that act by different mechanisms of action.

AREAS COVERED

In this narrative review, the authors discuss key points about CRPS definitions, diagnostic criteria and pitfalls, pathophysiological hypotheses, and treatment strategies with particular reference to pharmacotherapy. The article was based on a literature search using PubMed while the available guidelines for the management of CRPS were also examined.

EXPERT OPINION

According to the quality of evidence, pharmacological interventions for CRPS seem to be more effective all the more so when they act on peripheral mechanisms, particularly on nociceptive pain, and when applied early in the disease, while reliable evidence about central mechanisms of chronic pain in CRPS is lacking. In our opinion, drug therapy should be preferred as early as possible, particularly in warm forms of CRPS to prevent significant functional limitation, psychological distress, and social and economic fallout.

Botulinum toxin type A applications for masticatory myofascial pain and trigeminal neuralgia: what is the evidence regarding adverse effects?

OBJECTIVES

The objective of the study was to conduct a systematic review of literature assessing botulinum toxin type A (BoNT-A) safety and adverse effects in the treatment of myofascial pain (MFP) and trigeminal neuralgia (TN).

MATERIALS AND METHODS

The search for articles by two specific researchers involved the PubMed, EMBASE, Web of Science, and Scopus databases. Specific terms were used, and no publication time and language restrictions were applied. Clinical trials that investigated the effects of BoNT-A among participants with myofascial pain in masticatory muscles or trigeminal neuralgia were considered eligible for this systematic review. Data for each study were extracted and analyzed according to a PICO-like structured reading.

RESULTS

The search strategy provided 436 citations. After analysis, 16 citations were included, seven for MFP and nine for TN. In all studies, BoNT-A was well tolerated and improved pain. The most common adverse effects were temporary regional weakness, tenderness over the injection sites, and minor discomfort during chewing. Most studies reported a spontaneous resolution of adverse effect.

CONCLUSIONS

It can be concluded that BoNT-A treatment is well tolerated, since minor adverse effects were the most frequently reported; however, it is recommended that future studies aim to assess the safety and possible adverse effects of multiples applications or high doses of this treatment.

CLINICAL RELEVANCE

BoNT-A has been increasingly diffused in dentistry, being used for the management of masticatory myofascial pain and trigeminal neuralgia. Nonetheless, there is no consensus about its efficacy and adverse effects that could occur when this treatment is applied.

Botulinum toxin for chronic pelvic pain in women with endometriosis: a cohort study of a pain-focused treatment

BACKGROUND AND OBJECTIVES

Many women with endometriosis continue to have pelvic pain despite optimal surgical and hormonal treatment; some also have palpable pelvic floor muscle spasm. We describe changes in pain, spasm, and disability after pelvic muscle onabotulinumtoxinA injection in women with endometriosis-associated pelvic pain, a specific population not addressed in prior pelvic pain studies on botulinum toxin.

METHODS

We present an open-label proof-of-concept case series of women with surgically diagnosed endometriosis. Under conscious sedation and with topical anesthetic, 100 units of onabotulinumtoxinA was injected transvaginally into pelvic floor muscle spasm areas under electromyography guidance. Changes in pain intensity, muscle spasm, disability, and pain medication use were assessed at periodic visits for up to 1 year after injection.

RESULTS

Thirteen women underwent botulinum toxin injection and were followed for at least 4 months. Before injection, 11 of the 13 women had spasm in >4/6 assessed pelvic muscles and reported moderate pain (median visual analog scale (VAS): 5/10; range: 2-7). By 4-8 weeks after injection, spasm was absent/less widespread (≤3 muscles) in all (p=0.0005). Eleven rated their postinjection pain as absent/mild (median VAS: 2; range: 0-5; p<0.0001); 7/13 reduced pain medication. Disability decreased in 6/8 women with at least moderate preinjection disability (p=0.0033). Relief lasted 5-11 months in 7 of the 11 patients followed for up to 1 year. Adverse events were mild and transient.

CONCLUSIONS

These findings suggest pelvic floor spasm may be a major contributor to endometriosis-associated pelvic pain. Botulinum toxin injection may provide meaningful relief of pain and associated disability.

TRIAL REGISTRATION NUMBER

NCT01553201.

Interventions to chronic prostatitis/Chronic pelvic pain syndrome treatment. Where are we standing and what's next?

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is a frustrating syndrome. The pathogenesis and state of the art treatment of CP/CPPS are not known. A wide variety of therapies including anti-inflammatories, antibiotics, alpha-blockers, neuropathic pain modulators, and 5α-reductase inhibitors are in practice. These treatment strategies focus on alleviating symptoms in specific domains without treating root-cause and therapeutic outcome is far from satisfactory. We review the literature on current pharmacological treatments for CP/CPPS in detail and suggest future perspectives to modify the treatment strategies. We suggest that introducing novel treatment strategies such as gene editing, and T_regs expressing chimeric receptors may improve the treatment outcomes by inducing immune tolerance and controlling expression of pro-inflammatory cytokines.

Intra-articular botulinum toxin type A for treatment of knee osteoarthritis: Clinical trial

In recent years, there is a growing interest in new medical applications of botulinum toxin, including pain control, osteoarthritis treatment, and wound healing. While clinical applications of botulinum toxin seem promising, existing evidence regarding the therapeutic effects is still inadequate. The aim was to assess the efficacy of a single injection of abobotulinumtoxin A into the knee joint cavity to reduce pain in elderly people. We carried out a single group clinical trial in a University Hospital. Thirty participants (24 women) more than 50 years of age with knee osteoarthritis were included. Diagnosis of osteoarthritis was based on clinical and radiologic findings. We gave a single injection containing 250 units of Dysport (= 100 units of botulinum neurotoxin type A) diluted with 5 ml of normal saline. The primary outcome measure was knee pain. The secondary outcome was the patients' opinion about their knee and associated problems measured with the Knee injury and Osteoarthritis Outcome Score. The outcomes were measured at the baseline and at 4 weeks after the intervention. Within-group comparisons based on the Knee injury and Osteoarthritis Outcome Scores showed favorable results for joint pain and stiffness, sports, severity of symptoms, quality of life, and daily activities (all p-values < 0.001). Also, pain intensity, joint effusion, knee clicking and locking, and flexion-extension scores showed significant beneficial results (all p-values ≤ 0.005). We concluded that botulinum neurotoxin type A is an effective and safe initial treatment of knee osteoarthritis with clear clinical advantages. Patients' satisfaction, minimum adverse effects in addition to single-dose prescription make the toxin as a choice for the first-line therapy of osteoarthritis at least at the short-term in elderly people. The symptom relief increases the patient's compliance and willing to participate in other therapeutic programs. REGISTRATION: Iranian Registry of Clinical Trials (IRCT) website http://www.irct.ir/, a WHO Primary Register setup, with registration code: Irct ID: IRCT20180416039323N1.

Botulinum Toxin for Central Neuropathic Pain

Botulinum toxin (BTX) is widely used to treat muscle spasticity by acting on motor neurons. Recently, studies of the effects of BTX on sensory nerves have been reported and several studies have been conducted to evaluate its effects on peripheral and central neuropathic pain. Central neuropathic pain includes spinal cord injury-related neuropathic pain, post-stroke shoulder pain, multiple sclerosis-related pain, and complex regional pain syndrome. This article reviews the mechanism of central neuropathic pain and assesses the effect of BTX on central neuropathic pain.

Analgesic Effects of Botulinum Toxin in Children with CP

Experiencing pain is the greatest contributor to a reduced quality of life in children with cerebral palsy (CP). The presence of pain is quite common (~60%) and increases with age. This leads to missed school days, less participation, and reduced ambulation. Despite these alarming consequences, strategies to relieve the pain are absent and poorly studied. Moreover, it is difficult to evaluate pain in this group of children, especially in cases of children with cognitive deficits, and tools for pain evaluation are often inadequate. Botulinum toxin has been shown to alleviate pain in a variety of disorders and could potentially have an analgesic effect in children with CP as well. Even though most of the studies presented here show promising results, many also have limitations in their methodology as it is unlikely to capture all dimensions of pain in this heterogeneous group using only one assessment tool. In this review, we present a new way of examining the analgesic effect of botulinum toxin in children with CP using a variety of pain scores.