The efficacy of botulinum toxin for the treatment of trigeminal and postherpetic neuralgia: a systematic review with meta-analyses

Efficacy and safety of subcutaneous injection of botulinum toxin in the treatment of Chinese postherpetic neuralgia compared to analgesics: a systematic review of randomized controlled trials and meta-analysis

Objective

The purpose of this meta-analysis is to investigate the efficacy and safety of a subcutaneous injection of botulinum toxin in the treatment of postherpetic neuralgia (PHN) compared to analgesics.

Methods

We searched PubMed, Cochrane Library, Embase, Web of Science, Chinese National Knowledge Infrastructure (CNKI), and Wanfang for randomized controlled trials (RCTs) from inception to 10 September 2023. The primary clinical outcomes included visual analog scale (VAS) pain scores and clinical effective rates. The secondary clinical outcome included the adverse event rate during follow-up.

Results

A total of 14 studies with 1,358 participants were included in the meta-analysis. Among the included patients, 670 participants received botulinum toxin A injections and 688 participants received other medication treatments. The botulinum toxin-A (BTX-A) group exhibited lower pain scores [week 2: Mean difference (MD): -1.91, 95% confidence interval (CI): -2.63 to -1.20, and p < 0.00001; week 4: MD: -1.69, 95% CI: -2.69 to -0.68, and p < 0.00001; week 8: MD: -1.66, 95% CI: -2.20 to -1.12, and p < 0.00001; week 12:MD: -1.83, 95% CI: -2.70 to -0.96, and p < 0.00001; and week 24: MD: -1.07, 95% CI: -1.16 to -0.99, and p < 0.00001]. The effective rate was significantly higher in patients who received BTX-A for postherpetic neuralgia compared to those who received lidocaine or gabapentin (lidocaine: MD: -1.55, 95% CI: -2.84 to -0.27, and p = 0.02 and gabapentin: MD: -1.57, 95% CI: -2.12 to -1.02; and p < 0.00001). There was no difference in the incidence of adverse events between the treatment groups [odds ratio (OR): 1.25, 95% CI: 0.43 to 3.61, and p = 0.69].

Conclusion

Our meta-analysis showed that BTX-A has certain advantages in relieving postherpetic neuralgia compared to analgesics. In addition, BTX-A is safe for treating postherpetic neuralgia, with no notable side effects.

Systematic review registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42021289813.

Peripheral and central neurobiological effects of botulinum toxin A (BoNT/A) in neuropathic pain: a systematic review

ABSTRACT

Botulinum toxin (BoNT), a presynaptic inhibitor of acetylcholine (Ach) release at the neuromuscular junction (NMJ), is a successful and safe drug for the treatment of several neurological disorders. However, a wide and recent literature review has demonstrated that BoNT exerts its effects not only at the "periphery" but also within the central nervous system (CNS). Studies from animal models, in fact, have shown a retrograde transport to the CNS, thus modulating synaptic function. The increasing number of articles reporting efficacy of BoNT on chronic neuropathic pain (CNP), a complex disease of the CNS, demonstrates that the central mechanisms of BoNT are far from being completely elucidated. In this new light, BoNT might interfere with the activity of spinal, brain stem, and cortical circuitry, modulating excitability and the functional organization of CNS in healthy conditions. Botulinum toxins efficacy on CNP is the result of a wide and complex action on many and diverse mechanisms at the basis of the maladaptive plasticity, the core of the pathogenesis of CNP. This systematic review aims to discuss in detail the BoNT's mechanisms and effects on peripheral and central neuroplasticity, at the basis for the clinical efficacy in CNP syndromes.

Botulinum toxin-A as a treatment option for refractory idiopathic trigeminal neuralgia of the ophthalmic branch: a case report and literature review

Trigeminal neuralgia is one of the most common neurological pains affecting the head and neck and is associated with severe, lancinating, electrical pain episodes. The maxillary and mandibular branches are usually affected. The ophthalmic branch is rarely involved and, when present, it requires a comprehensive workup to rule out major conditions. Pharmacotherapy and surgery are the most common treatment options for this condition. Systemic medications may pose a wide range of side effects and effectiveness may decrease over time while surgery has inherent complications. Injectable onabotulinum toxins have been utilized for various applications in medicine and dentistry. There is, however, limited data on their use for the management of refractory trigeminal neuralgia of the ophthalmic branch. We present the case of a 58-year-old male diagnosed with refractory idiopathic trigeminal neuralgia affecting the ophthalmic branch, which was unresponsive to standard care and successfully managed with onabotulinum toxin type A. This treatment should be considered in cases of refractory trigeminal neuralgia prior to surgery. We reviewed the relevant literature concerning the application of Onabotulinum toxin A for managing trigeminal neuralgia of the ophthalmic branch. This case report and review aim to enlighten the application of Onabotulinum toxin A for managing refractory trigeminal neuralgia of the ophthalmic branch. Our case report and review show that Onabotulinum toxin A could be used for managing TN of the ophthalmic branch.

Pain Modulation in Chronic Musculoskeletal Disorders: Botulinum Toxin, a Descriptive Analysis

Botulinum neurotoxin (BoNT), a product of Clostridium botulinum, reversibly inhibits the presynaptic release of the neurotransmitter acetylcholine at the neuromuscular junction. In addition, BoNT blocks the transmission of other substances involved in pain perception and, together with a soft-tissue anti-inflammatory effect, may play a role in analgesia. When first-line treatment fails, second-line therapies might include BoNT. Studies on chronic and recurrent pain using different mechanisms offer heterogenous results that must be validated and standardized. Plantar fasciitis, severe knee osteoarthritis, painful knee and hip arthroplasty, antalgic muscular contractures, and neuropathic and myofascial pain syndromes may benefit from the administration of BoNT. Research on this topic has revealed the main musculoskeletal conditions that can benefit from BoNT, stressing the effects, modalities of administration, doses, and schedule.

Effects of Intradermal Botulinum Toxin Injections on Herpes Zoster Related Neuralgia

Background

Postherpetic neuralgia (PHN), which represents the most common chronic complication of herpes zoster, is characterized by intense pain and is difficult to treat. In fact, no treatments are currently available that can effectively reduce the pain associated with PHN. Recent evidence has been presented indicating that Botulinum toxin (BoNT-A) can serve as an effective and safe treatment for peripheral neuropathic pain.

Objective

The effects of intradermal BoNT-A injections on herpes zoster related neuralgia were investigated in this study.

Methods

Patients diagnosed with herpes zoster related acute neuralgia (N=13 - acute group) and those diagnosed with postherpetic neuralgia (N=17 - PHN group) were enrolled in this study. The two groups were treated with intradermal injections of BoNT-A at the site of their affected pain areas and were then assessed at 1 day, 1 week, 2 weeks, 1 month, 2 months and 3 months after their BoNT-A treatments.

Results

When compared with pre-treatment values, Visual Analogue Scores (VAS) in all patients were all significantly decreased at all times tested following BoNT-A injection. Before treatment, PHN patients had significantly higher VAS than those in the acute group. However, after 1 day of treatment, there was no difference in VAS between the two groups. None of the patients in the acute phase treated with BoNT-A developed PHN.

Conclusion

BoNT-A injections significantly reduced herpetic-related pain and proved to be a more effective treatment for the PHN versus acute pain group. Moreover, an early application of BoNT-A can alleviate the probability of developing PHN.

Neurotoxins Acting at Synaptic Sites: A Brief Review on Mechanisms and Clinical Applications

Neurotoxins generally inhibit or promote the release of neurotransmitters or bind to receptors that are located in the pre- or post-synaptic membranes, thereby affecting physiological functions of synapses and affecting biological processes. With more and more research on the toxins of various origins, many neurotoxins are now widely used in clinical treatment and have demonstrated good therapeutic outcomes. This review summarizes the structural properties and potential pharmacological effects of neurotoxins acting on different components of the synapse, as well as their important clinical applications, thus could be a useful reference for researchers and clinicians in the study of neurotoxins.

Efficacy and safety of botulinum A toxin for the treatment of chronic peripheral neuropathic pain: A systematic review of randomized controlled trials and meta-analysis

BACKGROUND AND OBJECTIVE

Botulinum toxin type A (BTX-A) is a recently developed treatment for the management of peripheral neuropathic pain. The objective of this study was to provide a synthesis of the evidence concerning the efficacy and safety of subcutaneous botulinum toxin type A injections.

DATABASES AND DATA TREATMENT

We searched the MEDLINE, EMBASE, LILACS, Cochrane, and Clinical Trial Register databases for randomized controlled trials comparing subcutaneous BTX-A to placebo injections for treating chronic peripheral neuropathic pain. The primary endpoint was the assessment of pain 1 month after the injection. The secondary outcomes were the assessment of pain at 3 months, neuropathic pain intensity and quality of life at 1 and 3 months, and adverse effects. A random-effect meta-analysis was performed on the combined data. Evidence quality was rated by the Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) method.

RESULTS

Ten randomized controlled trials including 505 patients were included in this review (registration number CRD42021239108). At 1 and 3 months after injection, the BTX-A groups had a lower mean difference (MD) in pain score (MD -1.87 (confidence intervals [CIs] -2.91; -0.83) and -1.38 (CI -1.95; -0.81), respectively). Subgroup analysis showed greater efficacy for diabetic polyneuropathy (MD -2.48, [-3.22; -1.74]). We found no impact of BTX-A on quality of life and no difference in adverse effect between BTX-A and placebo. The evidence was considered of moderate quality.

CONCLUSION

The pooled data suggest that subcutaneous BTX-A injections have a clinically significant effect, decreasing pain for three months after the injection, but no benefit in terms of quality of life has yet been demonstrated.

SIGNIFICANCE

We found that botulinum toxin is efficient and safe for the treatment of neuropathic pain, especially for diabetic polyneuropathy. Botulinum toxin type A, used for years in neurology, rehabilitation and physical medicine, has proved innocuous and effective, and should be considered as a serious alternative for pain treatment.

A Systematic Review and Meta-Analysis of Efficacy of Botulinum Toxin A for Neuropathic Pain

We performed a systematic review and meta-analysis of randomised controlled trials (RCTs) conducted from January 2005 to June 2021 to update the evidence of Botulinum toxin A (BoNT-A) in neuropathic pain (NP) in addition to quality of life (QOL), mental health, and sleep outcomes. We conducted a Cochrane Grading of Recommendations Assessment, Development, and Evaluation (GRADE) criteria analysis of RCTs from the following data sources: EMBASE, CINAHL, WHO International Clinical Trial Registry Platform, ClinicalTrials.gov, Cochrane database, Cochrane Clinical Trial Register, Australia New Zealand Clinical Trials Registry, and EU Clinical Trials Register. Meta-analysis of 17 studies showed a mean final VAS reduction in pain in the intervention group of 2.59 units (95% confidence interval: 1.79, 3.38) greater than the mean for the placebo group. The overall mean difference for sleep, Hospital Anxiety and Depression Scale (HADS) anxiety, HADS depression, and QOL mental and physical sub-scales were, respectively, 1.10 (95% CI: -1.71, 3.90), 1.41 (95% CI: -0.61, 3.43), -0.16 (95% CI: -1.95, 1.63), 0.85 (95% CI: -1.85, 3.56), and -0.71 (95% CI: -3.39, 1.97), indicating no significance. BoNT-A is effective for NP; however, small-scale RCTs to date have been limited in evidence. The reasons for this are discussed, and methods for future RCTs are developed to establish BoNT-A as the first-line agent.

Effectiveness of nonsurgical treatments for trigeminal neuralgia: an overview protocol

ABSTRACT Purpose: to present an overview protocol for systematic reviews to synthesize and describe available evidence on the effectiveness of nonsurgical treatments for trigeminal neuralgia. Methods: the protocol follows the method proposed by PRISMA-P guidelines for protocol reports. The search will be made in MEDLINE, EMBASE, LILACS, Cochrane, Web of Science, Scopus, SpeechBITE, PeDRO, and the grey literature (Google Scholar and ProQuest Dissertations and Theses), with no restriction on language or time of publication. A search strategy developed for MEDLINE will be adapted for each database. Two independent reviewers will screen the articles by title and abstract. Then, they will read the full texts of included articles, following the eligibility criteria. In case of disagreements, a third reviewer will come to a consensus. The data will be extracted with a standardized form. Information on the risk of bias and GRADE assessment will be recorded. AMSTAR-2 will assess the overall result reliability of the systematic reviews. Results will be presented in a flowchart, tables, and a narrative description. Final Considerations: once carried out, this protocol will describe the current body of research on the topic and identify existing gaps on the basis of evidence.

A efetividade dos tratamentos não cirúrgicos na neuralgia do trigêmeo: um protocolo de overview

RESUMO Objetivo: apresentar um protocolo de Overview das revisões sistemáticas (RSs) para sintetizar e descrever evidências disponíveis sobre a efetividade dos tratamentos não cirúrgicos na neuralgia do trigêmeo. Métodos: o protocolo seguirá o método proposto pelas diretrizes do PRISMA-P para relato de protocolos. A busca será realizada nas bases de dados eletrônicas: MEDLINE, EMBASE, Lilacs, COCHRANE, Web of Science, Scopus, SpeechBITE, PeDRO, além de consulta à literatura cinzenta (Google Scholar e ProQuest Dissertations and Theses), sem restrições de idioma ou período de publicação. Uma estratégia de busca foi desenvolvida para MEDLINE e será adaptada para cada base de dados. O rastreio dos artigos pelo título e resumo será realizado por dois revisores independentes. Em seguida, farão leitura dos textos completos dos artigos incluídos, conforme os critérios de elegibilidade. Em discordância, um terceiro revisor fará o consenso. Os dados serão extraídos por meio de um formulário padronizado. Serão registradas informações de risco de viés e avaliação do GRADE. A ferramenta AMSTAR II avaliará a confiança geral dos resultados das RSs. Os resultados serão apresentados em um fluxograma, tabelas e descrição narrativa. Considerações Finais: a execução deste protocolo descreverá o corpo atual de pesquisa sobre o tema e identificará lacunas existentes na base de evidências.

Efficacy and Safety of Moxibustion for Postherpetic Neuralgia: A Systematic Review and Meta-Analysis

Background: Postherpetic neuralgia (PHN) is one of the most common complications of herpes zoster (HZ), and there is still a lack of effective therapies. An increasing number of studies have found that compared to traditional therapy, moxibustion treatment is beneficial for the treatment of PHN, although current evidence remains inconclusive. This systematic review and meta-analysis of randomized controlled trials (RCTs) aimed to evaluate the efficacy and safety of moxibustion for PHN.

Methods: We conducted a broad literature review of a range of databases from inception to December 2020, including the Cochrane Library, PubMed, EMBASE, Web of Science, Clinical Trails, China National Knowledge Infrastructure (CNKI), VIP Database for Chinese Technical Periodicals (VIP), China Biomedical Network Information, and Wanfang databases. We included RCTs that compared moxibustion to pharmacological therapies, herbal medicine, or no treatment for treating PHN. The main outcome measure was efficacy rate and Visual Analog Scale (VAS); the secondary outcome measure was adverse events. Data accumulation and synthesis included meta-analysis, publication bias, sensitivity analysis, risk-of-bias assessment, and adverse events.

Results: We included 13 RCTs involving 798 patients. Compared with the controls (pharmacological therapies, herbal medicine, or no treatment), moxibustion achieved a significantly higher efficacy rate (odds ratio [OR]: 3.65; 95% [confidence interval]: [2.32, 5.72]; P < 0.00001). Subgroup analysis of the distinct moxibustion modalities showed that both Zhuang medicine medicated thread and thunder-fire moxibustions obtained higher clinical efficacy than the control group. Compared with the controls, moxibustion resulted in significantly lower scores on the VAS (Weighted Mean Difference (MD) = −1.79; 95% CI: [−2.26, −1.33]; P < 0.00001). However, there was no significant difference in terms of safety between moxibustion and the controls (OR = 0.33; 95% CI [0.06, 1.77]; P = 0.19).

Conclusion: Due to the lack of methodological quality as well as the significant heterogeneity of the included studies, it remains difficult to draw a firm conclusion on the efficacy and safety of moxibustion for the treatment of PHN. Future high-quality studies are urgently needed.

Incobotulinum toxin type A for treatment of chronic myofascial pain

PURPOSE

This study assessed the effectiveness of incobotulinum toxin type A (IBTx) for chronic myofascial pain affecting the masseter and temporal muscles.

METHODS

Twenty two patients who received a diagnosis of chronic masseter and temporalis myofascial pain were evaluated by using a visual analog pain scale (VAS), digital pressure algometry, and the SF-36 Health Survey at baseline (T0), before IBTx injection. Patients were again evaluated at 2 months (T1) and 7 months (T2) after IBTx injection.

RESULTS

VAS scores for pain significantly differed (P = 0.029, Friedman test). Post-hoc tests showed a significant reduction in pain at 2 months (T0-T1) and 7 months (T0-T2) (P = 0.011 and P = 0.028, respectively; Wilcoxon test) but not between 2 and 7 months (P = 0.676; Wilcoxon test). There was no significant difference in pressure algometry values (P = 0.385, Friedman test). Quality of life (QOL) assessment showed a significant difference (P = 0.002, Friedman test). Post-hoc tests showed a significant improvement in QOLat 2 months, but no significant difference at 7 months (P = 0.004 and P = 0.260, Wilcoxon test).

CONCLUSION

IBTx injection resulted in safe, effective short-term pain relief for patients with chronic facial pain affecting the masseter and temporalis muscles.

Craniofacial neuralgias

While non-headache, non-oral craniofacial neuralgia is relatively rare in incidence and prevalence, it can result in debilitating pain. Understanding the relevant anatomy of peripheral branches of nerves, natural history, clinical presentation, and management strategies will help the clinician better diagnose and treat craniofacial neuralgias. This article will review the nerves responsible for neuropathic pain in periorbital, periauricular, and occipital regions, distinct from idiopathic trigeminal neuralgia. The infratrochlear, supratrochlear, supraorbital, lacrimal, and infraorbital nerves mediate periorbital neuralgia. Periauricular neuralgia may involve the auriculotemporal nerve, the great auricular nerve, and the nervus intermedius. The greater occipital nerve, lesser occipital nerve, and third occipital nerve transmit occipital neuralgias. A wide range of treatment options exist, from modalities to surgery, and the evidence behind each is reviewed.

Chronic Facial Pain: Trigeminal Neuralgia, Persistent Idiopathic Facial Pain, and Myofascial Pain Syndrome-An Evidence-Based Narrative Review and Etiological Hypothesis

Trigeminal neuralgia (TN), the most common form of severe facial pain, may be confused with an ill-defined persistent idiopathic facial pain (PIFP). Facial pain is reviewed and a detailed discussion of TN and PIFP is presented. A possible cause for PIFP is proposed. (1) Methods: Databases were searched for articles related to facial pain, TN, and PIFP. Relevant articles were selected, and all systematic reviews and meta-analyses were included. (2) Discussion: The lifetime prevalence for TN is approximately 0.3% and for PIFP approximately 0.03%. TN is 15-20 times more common in persons with multiple sclerosis. Most cases of TN are caused by neurovascular compression, but a significant number are secondary to inflammation, tumor or trauma. The cause of PIFP remains unknown. Well-established TN treatment protocols include pharmacotherapy, neurotoxin denervation, peripheral nerve ablation, focused radiation, and microvascular decompression, with high rates of relief and varying degrees of adverse outcomes. No such protocols exist for PIFP. (3) Conclusion: PIFP may be confused with TN, but treatment possibilities differ greatly. Head and neck muscle myofascial pain syndrome is suggested as a possible cause of PIFP, a consideration that could open new approaches to treatment.

Botulinum Neurotoxin for the Treatment of Neuropathic Pain

Botulinum neurotoxin is widely used for the treatment of central and peripherical neurological conditions. Initially used to treat strabismus, over the years its use has been expanded also to spasticity and other neurological disorders. This review summarizes the evidence from the published literature regarding its effect on neuropathic pain. Almost all investigations were performed using onabotulinum toxin type A (BoNT/A). Most studies provided positive results, even though toxin formulation, dose, dilution, injection techniques, and sites are heterogeneous across studies. Future larger, high-quality, specifically designed clinical trials are warranted to confirm botulinum neurotoxin efficacy in neuropathic pain.

Guideline "diagnosis and non interventional therapy of neuropathic pain" of the German Society of Neurology (deutsche Gesellschaft für Neurologie)

2019 the DGN (Deutsche Gesellschaft für Neurology) published a new guideline on the diagnosis and non-interventional therapy of neuropathic pain of any etiology excluding trigeminal neuralgia and CRPS (complex regional pain syndrome). Neuropathic pain occurs after lesion or damage of the somatosensory system. Besides clinical examination several diagnostic procedures are recommended to assess the function of nociceptive A-delta and C-Fibers (skin biopsy, quantitative sensory testing, Laser-evoked potentials, Pain-evoked potentials, corneal confocal microscopy, axon reflex testing). First line treatment in neuropathic pain is pregabalin, gabapentin, duloxetine and amitriptyline. Second choice drugs are topical capsaicin and lidocaine, which can also be considered as primary treatment in focal neuropathic pain. Opioids are considered as third choice treatment. Botulinum toxin can be considered as a third choice drug for focal limited pain in specialized centers only. Carbamazepine and oxcarbazepine cannot be generally  recommended, but might be helpful in single cases. In Germany, cannabinoids can be prescribed, but only after approval of reimbursement. However, the use is not recommended, and can only be considered as off-label therapy within a multimodal therapy concept.

Botulinum neurotoxin injections for muscle-based (dystonia and spasticity) and non-muscle-based (neuropathic pain) pain disorders: a meta-analytic study

Apart from the known efficacy of Botulinum Neurotoxin Type A (BoNT/A) in hyperactive striated and smooth muscles, different pain states have become potential targets of toxin effects. This present study determined the comparative toxin effectiveness in pain reduction among those patients injected with BoNT/A in muscle-based and in non-muscle-based conditions. Randomized controlled trials (RCTs) on the effect of BoNT/A on selected pain conditions were included. The conditions were spasticity and dystonia for muscle-based pain. For non-muscle-based pain, conditions included were painful diabetic neuropathy (PDN), post-herpetic neuralgia (PHN), trigeminal neuralgia (TN), complex regional pain syndrome (CRPS), and spinal cord injury (SCI). In view of possibly differing pathophysiology, myofascial pain, temporomandibular joint (TMJ), other joint or tendon pains, cervicogenic and lumbar pains, migraine and visceral pain syndromes were excluded. Standardized mean difference was used as the effect measure and computed with STATA. 25 RCTs were analyzed. Pooled estimates showed significantly lower pain score in the Treatment group (z = 5.23, p < 0.01, 95% CI = - 0.75, - 0.34). Subgroup analyses showed that BoNT/A significantly reduced both muscle-based (z = 3.78, p < 0.01, 95% CI = - 0.72, - 0.23) and non-muscle-based (z = 3.37, p = 0.001, 95% CI = - 1.00, - 0.27) pain. Meta-regression using four covariates namely dosage, route, frequency and duration was done which revealed that dosage significantly affects standardized mean differences, while the other three covariates were insignificant. The joint F-test was found to be insignificant (p value = 0.1182). The application of the model with these covariates does not significantly explain the derived heterogeneity of standardized mean differences. In conclusion, BoNT/A can be effectively used in muscle-based and non-muscle-based pain disorders. We detected no difference between the presence and magnitude of pain relief favoring muscle-based compared to non-muscle-based pain. Thus, we cannot say whether or not there might be independent mechanisms of toxin-induced pain relief for pain generated from either muscle or nerve hyperactivity.

Botulinum toxin A treatment for post-herpetic neuralgia: A systematic review and meta-analysis

The present meta-analysis study aimed to investigate the safety and efficacy of local administration of botulinum toxin (BTX-A) vs. lidocaine in the treatment of post-herpetic neuralgia. A systematic search of the Cochrane Library, PubMed, Embase, Chinese National Knowledge Infrastructure, Wanfang, Chongqing VIP Information Co. and Chinese Biomedical Literature Database was performed to identify randomized controlled trials (RCTs) comparing BTX-A and lidocaine in the treatment of post-herpetic neuralgia. The primary outcomes were Visual Analogue Scale (VAS) pain scores at 1, 2 and 3 months after treatment and the effective rate. Secondary outcomes were scores on the McGill pain questionnaire and adverse event rate. A total of 7 RCTs comprising 752 patients were included. The VAS pain score was significantly lower at 1 month [mean difference (MD)=-2.31; 95% CI: -3.06, -1.56; P<0.00001)], 2 months (MD=-2.18; 95% CI: -2.24, -2.11; P<0.00001) and 3 months (MD=-1.93; 95% CI: -3.05, -0.82; P=0.0007) after treatment, the effective rate was significantly higher (odds ratio=2.9; 95% CI: 1.71, 4.13; P<0.0001) and scores on the McGill pain questionnaire were significantly lower (MD=-10.93; 95% CI: -21.02, -0.83; Z=2.12; P=0.03) in patients who received BTX-A for post-herpetic neuralgia compared to those who received lidocaine. There was no difference in the adverse event rate between treatments. In conclusion, BTX-A has potential as a safe and effective treatment option for post-herpetic neuralgia. Further large and well-designed RCTs are required to confirm this conclusion.

The efficacy and safety of botulinum toxin type A in treatment of trigeminal neuralgia and peripheral neuropathic pain: A meta-analysis of randomized controlled trials

BACKGROUND

Although recent studies have shown that botulinum toxin-A (BTX-A) has a good analgesic effect on trigeminal neuralgia (TN) and peripheral neuropathic pain (PNP), the quality of evidence is low due to limited data. This meta-analysis is used to synthesize existing evidence for the treatment of these conditions with BTX-A.

METHODS

Relevant trials were accessed by using an electronic search in databases (Web of Science, PubMed, EMBASE, Cochrane Library, and ClinicalTrials.gov). Data from included randomized controlled trials (RCTs) on the efficacy and safety of BTX-A in treating TN and PNP were extracted for meta-analysis.

RESULTS

Finally, 10 RCTs (n = 391) were included in this meta-analysis. The pooled effect of BTX-A was superior to placebo based on pain intensity (SMD = -0.48, 95% CI [-0.74, 0.23] at 1 month, SMD = -0.58, 95% CI [-0.91, -0.24] at 2 months, and SMD = -0.55, 95% CI [-0.87, -0.22] at 3 months). Number needed to treat (NNT) for 50% pain intensity reduction showed better effect of BTX-A on TN and postherpetic neuralgia (PN). Adverse events associated with BTX-A were similar to placebo (OR = 1.58, 95% CI [0.51, 4.87], p = .424).

CONCLUSION

Pooled data from our meta-analysis suggest that BTX-A is efficacious and safe in treating TN and PNP. However, due to the limited sample size and heterogeneity, further larger and well-designed RCTs are imperative to validate these findings.

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.

Treatment of non-odontogenic orofacial pain using botulinum toxin-A: a retrospective case series study

BACKGROUND

The purpose of this study was to evaluate the clinical outcomes of treatment of non-odontogenic atypical orofacial pain using botulinum toxin-A.

METHODS

This study involved seven patients (seven females, mean age 65.1 years) who had non-odontogenic orofacial pain (neuropathic pain and atypical orofacial pain) and visited the Seoul National University Bundang Hospital between 2015 and 2017. All medication therapies were preceded by botulinum toxin-A injections, followed by injections in the insignificant effects of medication therapies. Five of the seven patients received intraoral injections in the gingival vestibule or mucosa, while the remaining two received extraoral injections in the masseter and temporal muscle areas.

RESULTS

In five of the seven patients, pain after botulinum toxin-A injection was significantly reduced. Most of the patients who underwent surgery for dental implantation or facial nerve reconstruction recovered after injections. However, the pain did not disappear in two patients who reported experiencing persistent pain without any cause.

CONCLUSIONS

The use of botulinum toxin-A for the treatment of non-odontogenic neuropathic orofacial pain is clinically useful. It is more effective to administer botulinum toxin-A in combination with other medications and physical therapy to improve pain.

Botulinum toxin-A for the treatment of neuralgia: a systematic review and meta-analysis

AIM

This meta-analysis was performed to evaluate the efficacy and safety of botulinum toxin-A (BTX-A) for the treatment of neuralgia.

METHODS

We searched PubMed, EMBASE, and Cochrane databases to identify randomized controlled trials (RCTs) comparing BTX-A treatment with saline for alleviating neuropathic pain. Primary outcome measures were pain scores up to 24 weeks after treatment. Secondary outcomes were hours of sleep, Short Form-36 (SF-36) life quality questionnaire, and adverse events. We used Review Manager 5.3 for the data analyses.

RESULTS

Twelve RCTs were included (n=495). Pain scores in the BTX-A group were significantly lower compared to the saline group at 4 weeks (mean difference [MD] =-1.64, 95% CI [-3.21, -0.07], P=0.04), 12 weeks (MD =-1.49, 95% CI [-2.05, -0.93], P<0.00001), and 24 weeks (MD =-1.61, 95% CI [-2.81, -0.40], P=0.009). There were no significant differences in hours of sleep, SF-36 questionnaire, or the incidence of injection pain or hematoma between the two groups. No serious adverse events associated with BTX-A were noted. Fourteen out of 108 patients (12.9%) with trigeminal neuralgia experienced mild facial asymmetry after the BTX-A treatment.

CONCLUSION

Based on the current evidence, BTX-A may be an effective and safe option for the treatment of neuralgia. Due to the limited number of patients included in this meta-analysis, more trials are still needed to confirm these results.

Modalities in managing postherpetic neuralgia

Postherpetic neuralgia (PHN) is the most troublesome side effect of Herpes Zoster (HZ), which mainly affects the elderly and immunocompromised populations. Despite the current advancement of treatments, PHN persists in many individuals influencing their daily activities and reducing their quality of life. Anticonvulsants, antidepressants, topical therapies including lidocaine and capsaicin, and opioids, are the most widely used therapies for the treatment of PHN. These medications come with their adverse effects, so they should be used carefully with the elderly or with patients with significant comorbidities. Other measures like botulinum toxin, nerve blocks, spinal cord stimulation, and radiofrequency have also contributed significantly to the management of PHN. However, the efficacy, safety, and tolerability of these invasive methods need to be carefully monitored when administering them. Early diagnosis and early initiation of treatment can reduce the burden associated with PHN. The zoster vaccine has effectively reduced the incidence of HZ and PHN. In this article, we discuss the treatment options available for the management of PHN, mainly focusing on the efficacy and safety of different therapeutic modalities.

BoTN-A: The efficacy of botulinum toxin for the treatment of trigeminal and postherpetic neuralgia: a systematic review with meta-analyses

There is moderate evidence as to the efficacy of the use of botulinum toxin to treat trigeminal neuralgia and postherpetic neuralgia.

Botulinum toxin treatment of pain syndromes -an evidence based review

This review evaluates the existing level of evidence for efficacy of BoNTs in different pain syndromes using the recommended efficacy criteria from the Assessment and Therapeutic Subcommittee of the American Academy of Neurology. There is a level A evidence (effective) for BoNT therapy in post-herpetic neuralgia, trigeminal neuralgia, and posttraumatic neuralgia. There is a level B evidence (probably effective) for diabetic neuropathy, plantar fasciitis, piriformis syndrome, pain associated with total knee arthroplasty, male pelvic pain syndrome, chronic low back pain, male pelvic pain, and neuropathic pain secondary to traumatic spinal cord injury. BoNTs are possibly effective (Level C -one class II study) for female pelvic pain, painful knee osteoarthritis, post-operative pain in children with cerebral palsy after adductor release surgery, anterior knee pain with vastus lateralis imbalance. There is a level B evidence (one class I study) that BoNT treatment is probably ineffective in carpal tunnel syndrome. For myofascial pain syndrome, the level of evidence is U (undetermined) due to contradicting results. More high quality (Class I) studies and studies with different types of BoNTs are needed for better understanding of the role of BoNTs in pain syndromes.

Role of central versus peripheral opioid system in antinociceptive and anti-inflammatory effect of botulinum toxin type A in trigeminal region

BACKGROUND

Although botulinum toxin type A (BT-A) is approved for chronic migraine treatment, its site and mechanism of action are still elusive. Recently our group discovered that suppression of CGRP release from dural nerve endings might account for antimigraine action of pericranially injected BT-A. We demonstrated that central antinociceptive effect of BT-A in sciatic region involves endogenous opioid system as well. Here we investigated possible interaction of BT-A with endogenous opioid system within the trigeminal region.

METHODS

In orofacial formalin test we investigated the influence of centrally acting opioid antagonist naltrexone (2 mg/kg, s.c.) versus peripherally acting methylnaltrexone (2 mg/kg, s.c.) on BT-A's (5 U/kg, s.c. into whisker pad) or morphine's (6 mg/kg, s.c.) antinociceptive effect and the effect on dural neurogenic inflammation (DNI). DNI was assessed by Evans blue-plasma protein extravasation.

RESULTS

Naltrexone abolished the effect of BT-A on pain and dural plasma protein extravasation, whereas peripherally acting methylnaltrexone did not change either BT-A's effect on pain or its effect on dural extravasation. Naltrexone abolished the antinociceptive and anti-inflammatory effects of morphine, as well. However, methylnaltrexone decreased the antinociceptive effect of morphine only partially in the second phase of the test and had no significant effect on morphine-mediated reduction in DNI.

CONCLUSIONS

Morphine acts on pain in trigeminal region both peripherally and centrally, whereas the effect on dural plasma protein extravasation seems to be only centrally mediated. However, the interaction of BT-A with endogenous opioid system, with consequent inhibition of nociceptive transmission as well as the DNI, occurs primarily centrally.

SIGNIFICANCE

Botulinum toxin type A (BT-A)'s axonal transport and potential transcytosis suggest that its antinociceptive effect might involve diverse neurotransmitters at different sites of trigeminal system. Here we discovered that the reduction in pain and accompanying DNI involves the interaction of BT-A with central endogenous opioid system (probably at the level of trigeminal nucleus caudalis).

Post-herpetic neuralgia - a review of current management and future directions

Post-herpetic neuralgia (PHN) is common and treatment is often suboptimal with less than half of patients achieving adequate 50% pain relief. As an area of unmet clinical need and as an archetype of neuropathic pain, it deserves the attention of clinicians and researchers. Areas covered: This review summarises the epidemiology, pathophysiology, risk factors and clinical features of varicella infection. It describes the current and possible future management strategies for preventing varicella infection and reactivation and for treating PHN. Expert opinion: A highly successful Varicella Zoster (VZV) vaccine has not been universally adopted due to fears that it may increase Herpes Zoster (HZ) incidence - and thus PHN - in older, unvaccinated generations. This is a controversial theory but advances in the efficacy of vaccines against HZ may allay these fears and encourage more widespread adoption of the VZV vaccine. Treatment of PHN, as for any neuropathic pain, must be multidisciplinary and multimodal. Advances in sensory phenotyping technology and genomics may allow more individualised treatment. Traditional research methodologies are ill-suited to assess the kind of complex interventions that are necessary to achieve better clinical outcomes in this challenging field.

Neuropathic pain

Neuropathic pain is caused by a lesion or disease of the somatosensory system, including peripheral fibres (Aβ, Aδ and C fibres) and central neurons, and affects 7-10% of the general population. Multiple causes of neuropathic pain have been described and its incidence is likely to increase owing to the ageing global population, increased incidence of diabetes mellitus and improved survival from cancer after chemotherapy. Indeed, imbalances between excitatory and inhibitory somatosensory signalling, alterations in ion channels and variability in the way that pain messages are modulated in the central nervous system all have been implicated in neuropathic pain. The burden of chronic neuropathic pain seems to be related to the complexity of neuropathic symptoms, poor outcomes and difficult treatment decisions. Importantly, quality of life is impaired in patients with neuropathic pain owing to increased drug prescriptions and visits to health care providers, as well as the morbidity from the pain itself and the inciting disease. Despite challenges, progress in the understanding of the pathophysiology of neuropathic pain is spurring the development of new diagnostic procedures and personalized interventions, which emphasize the need for a multidisciplinary approach to the management of neuropathic pain.