Botulinum toxin A in postherpetic neuralgia: a parallel, randomized, double-blind, single-dose, placebo-controlled trial

The Trigeminal Nerve in Diabetes Mellitus: A Brief Narrative Review

This brief narrative review discusses the clinical manifestations, diagnosis, and management of trigeminal nerve-related conditions, such as neuropathy and neuralgia, in patients with diabetes mellitus. Although these conditions are not very common, there is a solid connection between them in diabetes patients. Symptoms typically include facial pain, sensory disturbances, and muscle weakness for neuropathy and severe, stabbing pain for neuralgia. Diagnosis is based on characteristic clinical manifestations, along with laboratory investigation and magnetic resonance imaging to exclude other potential causes, such as tumours, multiple sclerosis, or vascular compression. Treatment focuses on strict glycaemic control, modification of vascular risk factors, pharmacological agents (carbamazepine and oxcarbazepine), and neurostimulation to improve symptoms and quality of life.

Efficacy of Ultrasound-Guided Transverse Abdominal Plane Block for Residual Pain After Pulsed Radiofrequency in Abdominal Acute/Subacute Herpes Zoster-Related Pain

BACKGROUND

Pulse radiofrequency (PRF) can reduce the persistent pain of herpes zoster (HZ), but some patients still have residual pain and do not achieve satisfactory results. This study aimed to assess the efficacy of PRF combined with transverse abdominal plane (TAP) block for abdominal acute/subacute HZ-related pain.

METHODS

A total of 137 acute/sub-acute HZ patients with successful PRF treatment were recruited from the Pain Department of Wuhan No. 1 Hospital between January 2018 and January 2020. There were two groups: the transversus abdominis plane group (TAP group, n = 64) and the normal saline group (NS group, n = 60). Pain intensity, sleep quality, and quality of life were quantified using the visual analogue scale (VAS), the five-item questionnaire and scoring system, and the 36-item Short Form Health Survey (SF-36) questionnaire, respectively. Follow-up assessments were conducted at baseline, 1 day, 3 months, 6 months, and 12 months after the block therapy.

RESULTS

Compared to the NS group, the TAP group showed significantly decreased pain scores 1 day, 3 months, 6 months, and 12 months after block therapy (P < .05). The sleep quality scores were lower in the TAP group than that in the NS group at 6 months (5.0 ± 2.4 vs 6.3 ± 3.7, p = .042), and 12 months after therapy (3.1 ± 1.8 vs 4.1 ± 2.4, p = .031). For quality of life, in comparison to NS group participants, those in the TAP group exhibited significantly higher scores (p < .05) for quality of life at 3 months, 6 months, and 12 months follow-up. There was a significant decrease in the proportion of pregabalin and analgesic medications in the TAP group and NS group at 6 and 12 months after treatment compared to Baseline (p < .001). Furthermore, the results showed that there was a significant difference in VAS, sleep quality scores (SQS), and quality of life between the PRF + TAP group and pharmacological therapies group before and 12 months after treatment (p < .05).

CONCLUSION

The TAP block is a promising complementary treatment for acute/subacute HZ patients who have undergone PRF treatment. Combining PRF with the TAP block has the potential to alleviate HZ-related pain, enhance the patients' quality of life, and improve their sleep quality.

An update on botulinum toxin treatment of painful diabetic neuropathy, post-traumatic painful neuropathy/neuralgia, post-herpetic neuralgia and occipital neuralgia

The literature in botulinum toxin treatment for painful diabetic neuropathy (PDN), post traumatic neuralgia (PTN), postherpetic neuralgia (PHN) and occipital neuralgia (ON) was reviewed up to Oct 1st, 2024. Using the efficacy criteria set forth by the Assessment and Guideline subcommittee of the American Academy of Neurology, the current levels of efficacy for these conditions could be designated as followings: PDN: B (probably effective, two class II study), PTN: A (effective, two class I studies); PHN: A (effective, two class I studies), ON: (undetermined due to lack of blinded investigations). Due to the small number of patients in these studies, proof of efficacy requires conduction of controlled and blinded studies in large cohorts of patients with longer follow ups. Future prospects of botulinum therapy for these pain disorders were discussed along with the advantages of this mode of treatment over the current modes of treatment.

The efficacy of Botulinum Toxin in Tennis Elbow: a meta-analysis of randomized clinical trials

PURPOSE

This study aims to assess the efficacy of botulinum toxin type A (BT-A) in treating tennis elbow.

METHODS

We systematically reviewed the literature and included full-text randomized clinical trials (RCTs) published until June 2024, available in PubMed, Scopus, Embase, and Cochrane CENTRAL databases. Eligible studies involved patients with tennis elbow and compared BT-A with placebo or other injectable treatments. Primary outcomes included pain relief, while secondary outcomes assessed quality of life, adverse effects, and grip strength. The risk of bias was evaluated using the Cochrane Risk of Bias tool.

RESULTS

Seven RCTs with a total of 381 patients were included. The participants were predominantly middle-aged (mean age 46.64 ± 7.72 years) and diagnosed with chronic tennis elbow. BT-A doses ranged from 20U to 60U. Compared to placebo, BT-A effectively reduced pain at two to four weeks (MD = -1.37; 95% CI = -2.18 to -0.57) and at eight to 12 weeks (MD = -1.13; 95% CI = -1.62 to -0.65). Grip strength was comparable between the BT-A and placebo groups at both time points (2 to 4 weeks: SMD = -0.86; 95% CI -1.78 to 0.05; 8 to 12 weeks: SMD = 0.00; 95% CI = -0.95 to 0.95).

CONCLUSION

This meta-analysis suggests that BT-A reduces pain in tennis elbow within two to 12 weeks compared to placebo. Findings are limited by study size, and further research is needed to confirm its efficacy and safety.

Non-oral pharmacological interventions in the management of herpes zoster-related pain: a review of current research

Herpes zoster-associated pain is a difficult-to-treat pathologic pain that seriously affects patients' quality of life. In recent years, emerging therapeutic techniques such as autologous platelet-rich plasma, sympathetic nerve block and pulsed radiofrequency have been gradually applied in the field of pain with the advantages of less trauma, quicker recovery and significant efficacy. These therapeutic options have become a new hope for the treatment of herpes zoster-associated pain. This article reviews the studies on herpes zoster-associated pain in non-oral drug therapy, summarizes the efficacy, safety, and possible mechanisms, and provides a reference basis for clinical treatment.

Ultrasound combined with DSA-guided pulsed radiofrequency for perineal herpes zoster pain management: clinical outcomes and complications

Background

Herpes zoster (HZ) in the perineal area is a rare disease. There are limited treatment options for this disease. This study aimed to assess the efficacy of ultrasound combined with digital subtraction angiography (DSA)-guided pulsed radiofrequency (PRF) for perineal herpes zoster-related pain.

Methods

Two hundred and twelve patients with perineal HZ were enrolled at the pain department. From January 1, 2018 to December 30, 2019, patients with HZ in the perineal area were treated with PRF under DSA guidance, and from January 1, 2020 to October 30, 2023, patients with HZ in the perineal area were treated with PRF under ultrasound combined with DSA guidance. The included patients were divided into two groups: DSA group and ultrasound + DSA group. The visual analog scale (VAS), central sensitization inventory (CSI), sleep quality scores (SQS), the 36-Item Short Form Health Survey questionnaire (SF-36) at baseline and after the PRF treatment were analyzed to evaluate clinical efficacy.

Results

The mean VAS scores, CSI scores, SQS, and SF-36 scores were statistically significantly lower after treatment compared to baseline (p < 0.001). There was no significant change in VAS scores, CSI scores, SQS, and SF-36 scores between the DSA group and the ultrasound + DSA group (p > 0.05). The time it took from the start of the puncture to the successful puncture was significantly shorter in the ultrasound + DSA group compared to the DSA group (41.2 ± 21.2 vs. 48.1 ± 20.3, p = 0.035). The ultrasound + DSA group had a higher percentage of satisfaction with the procedure than the DSA group (90/99, 90.9% vs. 62/78, 79.5%, p = 0.030). A total of 27 postoperative complications occurred. The incidence of puncture site hematoma was significantly higher in the DSA group (10/78, 12.8%) than that in the ultrasound + DSA group (4/99, 4.0%) (p = 0.032).

Conclusion

PRF can reduce pain from HZ in the perineal region, alleviate central sensitization, enhance sleep quality, and improve overall quality of life. When PRF is performed under ultrasound guidance combined with DSA, it shortens the puncture time and reduces the risk of hematoma formation at the puncture site, making it the recommended method for clinical use.

Evaluating the efficacy of botulinum toxin in treating complex regional pain syndrome: A systematic review

Complex Regional Pain Syndrome (CRPS) is characterized by pain, swelling, limited range of motion, skin changes, vasomotor instability, and bone demineralization. This study aims to assess the efficacy of botulinum toxin type A (BoNT-A) in the treatment of CRPS. We conducted a systematic literature review following the PRISMA guidelines, using the PICO strategy (Patient, Intervention, Comparison and Outcome) with the following criteria: P = Patients with CRPS; I = Botulinum toxin; C = Placebo or active drug; and O = Pain relief. Three randomized controlled trials with placebo controls were included, involving a total of 64 patients, 36 of whom received BoNT-A in doses ranging from 40U to 200U. The studies examined both lumbar sympathetic block and local application methods. Botulinum toxin shows promise in alleviating pain associated with CRPS, particularly when used as an adjunct to lumbar sympathetic blockade. However, the limited number of studies and small sample sizes impede reaching definitive conclusions regarding its efficacy and safety. Notably, local applications (intradermal or subcutaneous) require further investigation, as current evidence is insufficient and reports indicate patient discomfort. While preliminary findings suggest potential benefits of BoNT-A in managing CRPS, larger randomized trials are necessary to confirm its efficacy and safety.

The efficacy of botulinum toxin in neuropathic pain: a systematic review

Introduction

Neuropathic pain (NP) is characterised as a lesion or disease directly affecting the somatosensory system. This study aims to analyse the efficacy of botulinum toxin type A (BT-A) in the treatment of neuropathic pain.

Methods

This systematic literature review, guided by PRISMA, applied the PICO strategy with the following criteria: (P = patients with neuropathic pain, I = botulinum toxin, C = placebo or active drug, and O = pain relief).

Results

Fourteen articles, all randomised controlled trials with a placebo control, were included in the review. A total of 645 patients were randomised, with 353 patients receiving treatment with botulinum toxin type A in doses ranging from 25U to 400U. The evaluated studies addressed trigeminal neuralgia, diabetic polyneuropathy, post-herpetic neuralgia, spinal cord injury, phantom limb pain, and peripheral neuropathic pain after trauma or surgery.

Conclusion

BT-A has emerged as a promising treatment for various origins of neuropathic pain. Therefore, future studies should adopt stricter criteria regarding dosage and routes of administration to ensure effective and consistent BT-A application.

Botulinum toxin type A-targeted SPP1 contributes to neuropathic pain by the activation of microglia pyroptosis

BACKGROUND

Neuropathic pain (NP) is the primary symptom of various neurological conditions. Patients with NP often experience mood disorders, particularly depression and anxiety, that can severely affect their normal lives. Microglial cells are associated with NP. Excessive inflammatory responses, especially the secretion of large amounts of pro-inflammatory cytokines, ultimately lead to neuroinflammation. Microglial pyroptosis is a newly discovered form of inflammatory cell death associated with immune responses and inflammation-related diseases of the central nervous system.

AIM

To investigate the effects of botulinum toxin type A (BTX-A) on microglial pyroptosis in terms of NP and associated mechanisms.

METHODS

Two models, an in vitro lipopolysaccharide (LPS)-stimulated microglial cell model and a selective nerve injury model using BTX-A and SPP1 knockdown treatments, were used. Key proteins in the pyroptosis signaling pathway, NLRP3-GSDMD, were assessed using western blotting, real-time quantitative polymerase chain reaction, and immunofluorescence. Inflammatory factors [interleukin (IL)-6, IL-1β, and tumor necrosis factor (TNF)-α] were assessed using enzyme-linked immunosorbent assay. We also evaluated microglial cell proliferation and apoptosis. Furthermore, we measured pain sensation by assessing the delayed hind paw withdrawal latency using thermal stimulation.

RESULTS

The expression levels of ACS and GSDMD-N and the mRNA expression of TNF-α, IL-6, and IL-1β were enhanced in LPS-treated microglia. Furthermore, SPP1 expression was also induced in LPS-treated microglia. Notably, BTX-A inhibited SPP1 mRNA and protein expression in the LPS-treated microglia. Additionally, depletion of SPP1 or BTX-A inhibited cell viability and induced apoptosis in LPS-treated microglia, whereas co-treatment with BTX-A enhanced the effect of SPP1 short hairpin (sh)RNA in LPS-treated microglia. Finally, SPP1 depletion or BTX-A treatment reduced the levels of GSDMD-N, NLPRP3, and ASC and suppressed the production of inflammatory factors.

CONCLUSION

Notably, BTX-A therapy and SPP1 shRNA enhance microglial proliferation and apoptosis and inhibit microglial death. It improves pain perception and inhibits microglial activation in rats with selective nerve pain.

Efficacy of Botulinum Type A Injection for the Treatment of Postherpetic Neuralgia and Pruritus Persisting for More Than Four Years-A Case Report

Background: Postherpetic neuralgia (PHN) and postherpetic pruritus (PHP) are common complications of shingles that affect patients' quality of life. PHN and PHP can be managed using various medications and interventional procedures; however, complications persisting for at least six months may hamper recovery. Subcutaneous injections of botulinum toxin type A (BTX-A) can control persistent PHN and PHP. Case presentation: A 71-year-old man presented at our hospital with itching and pain. He had been diagnosed with shingles in the ophthalmic branch of the trigeminal nerve one year previously. As the pain and itching persisted despite medication, a supraorbital nerve block, Gasserian ganglion block, epidural nerve block, and radiofrequency thermocoagulation were performed. A subcutaneous injection of BTX-A was administered into the ophthalmic area of the trigeminal nerve three years after the initial presentation. A decrease of >80% in pain and itching was reported after the injection; however, the left eyelid drooped and the eyeball shifted downward and outward immediately after the injection. No deterioration in vision or pupil dilation was observed, and almost complete resolution of these symptoms occurred spontaneously three months after the injection. Pain and itching continued to improve without further side-effects until six months after the injection. Conclusions: The subcutaneous injection of BTX-A may be an alternative treatment option for chronic and refractory neurological diseases such as PHN and PHP, which persist for four years and are resistant to conventional treatments. Nevertheless, care must be taken to minimize the risk of ptosis.

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.

Neurobiological mechanisms of botulinum neurotoxin-induced analgesia for neuropathic pain

Botulinum neurotoxins (BoNTs) are a family of neurotoxins produced by Clostridia and other bacteria that induce botulism. BoNTs are internalized into nerve terminals at the site of injection and cleave soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins to inhibit the vesicular release of neurotransmitters. BoNTs have been approved for multiple therapeutic applications, including the treatment of migraines. They have also shown efficacies for treating neuropathic pain, such as diabetic neuropathy, and postherpetic and trigeminal neuralgia. However, the mechanisms underlying BoNT-induced analgesia are not well understood. Peripherally administered BoNT is taken up by the nerve terminals and reduces the release of glutamate, calcitonin gene-related peptide, and substance P, which decreases neurogenic inflammation in the periphery. BoNT is retrogradely transported to sensory ganglia and central terminals in a microtubule-dependent manner. BoNTs decrease the expression of pronociceptive genes (ion channels or cytokines) from sensory ganglia and the release of neurotransmitters and neuropeptides from primary afferent central terminals, which likely leads to decreased central sensitization in the dorsal horn of the spinal cord or trigeminal nucleus. BoNT-induced analgesia is abolished after capsaicin-induced denervation of transient receptor potential vanilloid 1 (TRPV1)-expressing afferents or the knockout of substance P or the neurokinin-1 receptor. Although peripheral administration of BoNT leads to changes in the central nervous system (e.g., decreased phosphorylation of glutamate receptors in second-order neurons, reduced activation of microglia, contralateral localization, and cortical reorganization), whether such changes are secondary to changes in primary afferents or directly mediated by trans-synaptic, transcytotic, or the hematogenous transport of BoNT is controversial. To enhance their therapeutic potential, BoNTs engineered for specific targeting of nociceptive pathways have been developed to treat chronic pain. Further mechanistic studies on BoNT-induced analgesia can enhance the application of native or engineered BoNTs for neuropathic pain treatment with improved safety and efficacy.

Effect of ultrasound-guided injection of botulinum toxin type A into shoulder joint cavity on shoulder pain in poststroke patients: study protocol for a randomized controlled trial

BACKGROUND

Hemiplegic shoulder pain (HSP) is a common complication after stroke. It severely affects the recovery of upper limb motor function. Early shoulder pain in hemiplegic patients is mainly neuropathic caused by central nerve injury or neuroplasticity. Commonly used corticosteroid injections in the shoulder joint can reduce shoulder pain; however, the side effects also include soft tissue degeneration or increased tendon fragility, and the long-term effects remain controversial. Botulinum toxin injections are relatively new and are thought to block the transmission of pain receptors in the shoulder joint cavity and inhibit the production of neuropathogenic substances to reduce neurogenic inflammation. Some studies suggest that the shoulder pain of hemiplegia after stroke is caused by changes in the central system related to shoulder joint pain, and persistent pain may induce the reorganization of the cortical sensory center or motor center. However, there is no conclusive evidence as to whether or not the amelioration of pain by botulinum toxin affects brain function. In previous studies of botulinum toxin versus glucocorticoids (triamcinolone acetonide injection) in the treatment of shoulder pain, there is a lack of observation of differences in changes in brain function. As the content of previous assessments of pain improvement was predominantly subjective, objective quantitative assessment indicators were lacking. Functional near-infrared imaging (fNIRS) can remedy this problem.

METHODS

This study protocol is designed for a double-blind, randomized controlled clinical trial of patients with post-stroke HSP without biceps longus tenosynovitis or acromion bursitis. Seventy-eight patients will be randomly assigned to either the botulinum toxin type A or glucocorticoid group. At baseline, patients in each group will receive shoulder cavity injections of either botulinum toxin or glucocorticoids and will be followed for 1 and 4 weeks. The primary outcome is change in shoulder pain on the visual analog scale (VAS). The secondary outcome is the assessment of changes in oxyhemoglobin levels in the corresponding brain regions by fNIRS imaging, shoulder flexion, external rotation range of motion, upper extremity Fugl-Meyer, and modified Ashworth score.

DISCUSSION

Ultrasound-guided botulinum toxin type A shoulder joint cavity injections may provide evidence of pain improvement in patients with HSP. The results of this trial are also help to analyze the correlation between changes in shoulder pain and changes in cerebral hemodynamics and shoulder joint motor function.

TRIAL REGISTRATION

Chinese clinical Trial Registry, ChiCTR2300070132. Registered 03 April 2023, https://www.chictr.org.cn/showproj.html?proj=193722 .

Efficacy of Paravertebral Injection of Interferon-α2b Combined with High-Voltage, Long-Term Pulsed Radiofrequency in DRG in Mitigation of Postherpetic Neuralgia: A Retrospective Study

OBJECTIVE

This investigation aims to evaluate the effectiveness of the paravertebral injection of recombinant human interferon-α2b in conjunction with high-voltage, long-term, pulsed radiofrequency (PRF) in the dorsal root ganglion for the mitigation of postherpetic neuralgia (PHN).

METHODS

This retrospective study included 84 individuals with acute PHN. The participants were divided into 3 groups. Group H was treated with interferon-α2b combined with high-voltage long-term PRF. Group C was treated with a combination of high-voltage, long-term PRF and a paravertebral injection (without recombinant human interferon-α2b), and group I was treated with interferon-α2b only. All the patients in the 3 groups were orally administered a 5-mg morphine hydrochloride quick-release tablet when a burst of pain occurred during treatment. The numerical rating scale for pain score, the interleukin-6 and galectin-3 levels, and the incidence of PHN were documented before and after therapy.

RESULTS

The pain intensity of all individuals decreased after therapy. Compared with group C, the numerical rating scale scores for group H were significantly reduced at 4, 8, and 12 weeks following therapy, and the PHN incidence was significantly lower. Compared with prior treatment, the recommended dosage of gabapentin capsules and immediate-release morphine hydrochloride tablets was reduced for group H. Compared with group C, the requirement for orally administrated gabapentin capsules and morphine hydrochloride tablets in group H was reduced significantly after treatment. No serious adverse reactions occurred in any of the 3 groups.

CONCLUSIONS

Within the context of treatment of acute PHN, the injection of interferon-α2b in conjunction with high-voltage, long-term application of PRF is more effective than PRF or the injection of interferon-α2b alone.

Is Botulinum Toxin Effective in Treating Orofacial Neuropathic Pain Disorders? A Systematic Review

BACKGROUND

The aim of this paper is to provide a systematic review of the literature regarding the clinical use of botulinum toxin (BTX) to treat various orofacial neuropathic pain disorders (NP).

METHODS

A comprehensive literature search was conducted using Medline, Web of Science, and the Cochrane Library databases. Only randomized clinical trials (RCT) published between 2003 and the end of June 2023, investigating the use of BTX to treat NP, were selected. PICO guidelines were used to select and tabulate the articles.

RESULTS

A total of 6 RCTs were selected. Five articles used BTX injections to treat classical trigeminal neuralgia, and one to treat post-herpetic neuralgia. A total of 795 patients received BTX injections. The selected studies utilised different doses and methods of injections and doses. All the selected studies concluded superiority of BTX injections over placebo for reducing pain levels, and 5 out 6 of them highlighted an improvement in the patient's quality of life. Most of the studies reported transient and mild side effects.

CONCLUSION

There is evidence of the efficacy of BTX injections in orofacial pain management. However, improved study protocols are required to provide direction for the clinical use of BTX to treat various orofacial neuropathic pain disorders.

A Case Report of Refractory Postherpetic Neuralgia After Ramsay Hunt Syndrome Treated With Tympanic Nerve Neurectomy

Ramsay Hunt syndrome is a facial nerve palsy that arises from herpes zoster infection. In rare cases, postherpetic neuralgia is a complication following Ramsay Hunt syndrome. Pain management to address postherpetic neuralgia includes facial nerve blocks, medications such as gabapentin, carbamazepine and botulinum toxin injections, and pulsed radiofrequency. Despite the reported benefits for patients with glossopharyngeal nerve pain, neurectomy as a treatment has rarely been described. A 45-year-old patient visited our ENT clinic for chronic right-sided facial, ear, and jaw pain that persisted for 9 years following the development of Ramsay Hunt syndrome. She trialed multiple medications including gabapentin, carbamazepine, and botulinum toxin injections with minimal relief to her symptoms. The patient underwent a diagnostic myringotomy with topical application of lidocaine to the tympanic nerve. This resulted in temporary relief of her pain until the effects of the lidocaine subsided. The patient was subsequently offered lysis of the right tympanic nerve for more definitive management. The patient experienced significant pain reduction after the right tympanic neurectomy procedure. Chronic postherpetic neuralgia following Ramsay Hunt syndrome can cause significant impairment in a patient's quality of life. For patients with ear pain refractory to conservative management, a tympanic neurectomy can be considered.

Pain Management in Dermatology

BACKGROUND

The dermatologist has to deal with many situations where the patient feels pain and must therefore know how to manage it.

SUMMARY

The aim of this review was to explore the treatments available to manage pain in dermatology in different circumstances, with an emphasis on pharmacological and non-pharmacological interventions specifically studied in dermatology.

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.

Botulinum toxin A and neuropathic pain: An update

Botulinum toxin type A is a widely used neurotoxin for the treatment of muscle hyperactivity such as dystonia and spasticity. Several clinical trials have also reported an efficacy of subcutaneous or intradermal administrations of botulinum toxin A on various neuropathic pain conditions including idiopathic trigeminal neuralgia and found that specific sensory phenotypes were predictors of the response. This narrative review summarizes the potential mechanisms of action, efficacy and safety of botulinum toxin A in neuropathic pain as well as its place in the therapeutic algorithm of neuropathic pain.

Analgesic Effect of Perineural Injection of BoNT/A on Neuropathic Pain Induced by Chronic Constriction Injury of Sciatic Nerve in Rats

This study was designed to investigate the analgesic effect of perineural injection of BoNT/A on neuropathic pain induced by sciatic nerve chronic constriction injury (CCI) and possible mechanisms. SD rats were randomly divided into Sham group, CCI group and BoNT/A group. Paw mechanical withdrawal threshold (pMWT) and paw thermal withdrawal latency (pTWL) of each group were detected at different time points after surgery. The expression of myelin markers, autophagy markers and NLRP3 inflammasome-related molecules in injured sciatic nerves were examined at 12 days after surgery. Moreover, C-fiber evoked potential in spinal dorsal horn was recorded. The expression of SNAP-25, neuroinflammation and synaptic plasticity in spinal dorsal horn of each group were examined. Then rats treated with BoNT/A were randomly divided into DMSO group and Wnt agonist group to further explore the regulatory effect of BoNT/A on Wnt pathway. We found that pMWT and pTWL of ipsilateral paw were significantly decreased in CCI group compared with Sham group, which could be improved by perineural injection of BoNT/A at days 7, 9 and 12 after surgery. The peripheral analgesic mechanisms of perineural injection of BoNT/A might be related to the protective effect on myelin sheath by inhibiting NLRP3 inflammasome and promoting autophagy flow, while the central analgesic mechanisms might be associated with inhibition of neuroinflammation and synaptic plasticity in spinal dorsal horn due to inhibiting SNAP-25 and Wnt pathway. As a new route of administration, perineural injection of BoNT/A can relieve CCI induced neuropathic pain probably via both peripheral and central analgesic mechanisms.

Analgesic Treatment Approach for Postherpetic Neuralgia: A Narrative Review

Post-herpetic neuralgia (PHN) is an entity derived from peripheral nerve damage that occurs during the reactivation of the Varicella Zoster Virus (VZV), which manifests itself through pain with neuropathic characteristics. This can prove to be very difficult to manage in the chronic stages of disease reappearance. There currently exists a multitude of treatment alternatives for PHN, however, prevention through the early initiation of antiviral regimens is vital. There are various pharmacological options available, but it is important to individualize each patient to maximize efficacy and minimize adverse effects. Interventional procedures have become a cornerstone in difficult-to-manage cases, and have shown promising outcomes when used in a multimodal approach by experienced specialists. It is necessary to make an objective diagnosis of PHN and start early treatment. Additionally there is current evidence that vouches for interventional therapies as well as individualization, with a clear establishment of therapeutic objectives according to the needs of each patient.

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.

Reasons and Determinants of BoNT-A Treatment Discontinuation in Patients Living with Spasticity: A 10-Year Retrospective Analysis

BACKGROUND

The present study aimed to evaluate the reasons and determinants of BoNT-A discontinuation in patients with stroke, multiple sclerosis, spinal cord injury, and traumatic brain injury.

METHODS

It is a retrospective study of 56 discontinuer patients treated with botulinum toxin between January 2011 and December 2021. Discontinuation rates and their predictors were estimated using Kaplan-Meier, Log rank test, and Cox's regression method of analyses.

RESULTS

The mean age was 56.54 years, 53.57% were affected by post-stroke spasticity, 17.86% by spinal cord injury, 12.5% and 16.07% by traumatic brain injury and multiple sclerosis, respectively. The median discontinuation time was 5 months. The main reason for discontinuation were logistic problems (37%) and orthopedic surgeries or intrathecal baclofen (27%). Discontinuers were more likely to have severe spasticity (R = 1.785), have no pain (HR = 1.320), no access to rehabilitation services (HR = 1.402), and have cognitive impairment (HR = 1.403).

CONCLUSIONS

The main reasons for discontinuation are related to logistic issues (due to distance or the absence of an adequate caregiver) and surgical interventions for spasticity, including intrathecal baclofen. It is crucial to identify possible predictors of discontinuation to improve the effectiveness of a multidisciplinary management. The study confirms the crucial role of rehabilitation and caregivers in achieving better long-term outcomes.

Botulinum toxin A for management of refractory concurrent buccal and inferior alveolar nerve post-traumatic neuropathies: a case report

Painful post-traumatic trigeminal neuropathy (PPTTN) can result from iatrogenic injury to one or more branches of the trigeminal nerve during oral surgical procedures such as tooth extractions. Like other chronic neuropathic pain conditions, PPTTN can significantly alter the patient’s quality of life, especially when pharmacological treatment is ineffective or not tolerated. As such, new treatment options have been investigated, including local injections of botulinum toxin type A (BTX-A). A 29-year-old woman presented to our tertiary orofacial pain clinic for evaluation of chronic electric shock-like pain attacks and severe allodynia in the territory of the right inferior alveolar nerve and buccal nerve following right mandibular third molar extraction 3 years prior. Following several failed attempts at classic pharmacological management (including carbamazepine, venlafaxine, duloxetine, pregabalin, clonazepam, and amitriptyline), BTX-A injections were administered in the vicinity of the right mental nerve. This treatment provided significant improvement in the patient’s condition and overall quality of life with no significant adverse effects. Because both neuropathies were significantly improved by remote BTX-A injections, this case report provides preliminary clinical evidence supporting spinopetal transport of BTX-A, as shown in animal models, as an underlying pathophysiological mechanism of BTX-A-mediated analgesia.

Phenotypes and Genotypes in Postherpetic Neuralgia Drug Therapy: A Narrative Mini-review

Neuropathic pain is a debilitating symptom reported by patients presenting with postherpetic neuralgia (PHN). Efforts to alleviate this pain have been projected to lie in individualization of pharmacological treatment through pain phenotyping and subsequent investigations into the genetic basis of PHN therapy. Understanding the various mechanisms related to these phenotypes can aid in improvement of available treatment options and discovery of new ones. Knowledge and application of genetic variations in PHN, structural proteins, and genes can aid in ascertaining risk, susceptibility to, severity of, and protection from PHN. This review summarizes the most recent information that has been published on phenotypes and genotypes with possible clinical applications and directions for future research.

Efficacy and Safety of Botulinum Toxin A and Pulsed Radiofrequency on Postherpetic Neuralgia: A Randomized Clinical Trial

This study evaluated the effectiveness and safety of botulinum toxin type A (BoNT-A) and pulsed radiofrequency (RF) in the clinical treatment of postherpetic neuralgia (PHN). A total of 100 patients with PHN were randomly divided into two groups (n = 50 per group): RF group and BoNT-A group. Based on conventional drug treatment, patients were treated with either a single nerve root pulsed radiofrequency therapy or a single local subcutaneous injection of BoNT-A in the lesion area. All the patients were followed up for 24 weeks on pain scores, sleep quality, anxiety, and depression scores, etc. In the last follow-up at the end of 24 weeks postoperation, the pain scores of patients in both groups were significantly lower than those before the operation (P < 0.05), indicating that both treatments were effective against PHN; however, there was no significant difference between these two groups (P > 0.05). It is noteworthy that the subcutaneous injection of BoNT-A is relatively easy to administer and less expensive compared to RF. Therefore, we believe that the subcutaneous injection of BoNT-A is an effective and safe method for the treatment of PHN.

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.

Multidimensional Effectiveness of Botulinum Toxin in Neuropathic Pain: A Systematic Review of Randomized Clinical Trials

Although botulinum toxin (BoNT) has been suggested as a treatment to counter neuropathic pain, no previous systematic reviews investigated the multidimensional effects of BoNT on pain relief and Health-Related Quality of Life (HR-QoL). The aim of this systematic review is to summarize the current evidence on the effectiveness of BoNT treatment for neuropathic pain, and to characterize its multidimensional effectiveness in order to guide physicians in clinical practice. Five databases were systematically searched up to 4 April 2022, to identify randomized controlled trials satisfying the following criteria: adults suffering from neuropathic pain, BoNT administration, any comparator, multidimensional assessment of pain as primary outcome, HR-QoL, physical function, anxiety and depression, and sleep quality as secondary outcomes. Twelve studies were included. The multidimensional pain scales used were short-form McGill Pain Questionnaire, Neuropathic pain scale, Neuropathic Pain Symptom Inventory, International SCI Pain Basic Data Set, West Haven-Yale Multidimensional Pain Inventory, Brief Pain Inventory, and Douleur Neuropathique 4. These scales highlighted the positive effects of BoNT administration. According to the Jadad scale, all the RCTs included were high-quality studies. BoNT administration might be effectively introduced in the comprehensive management of neuropathic pain. Further research should focus on optimal and cost-effective therapeutic protocols.

Serial Thoracic Transforaminal Epidural Steroid Injections for Post-herpetic Neuralgia: A Case Report

The chronic neuropathic pain of post-herpetic neuralgia (PHN) often persists for months or years after the acute herpes zoster (shingles) episode, may be severe and intractable, and can severely impact the overall quality of life. Antivirals, analgesics, and nerve blocks can effectively shorten the course of shingles and may help to prevent PHN. Although vaccination effectively prevents shingles and PHN, current therapies may be ineffective, and pain management can be challenging when PHN occurs. A 78-year-old female with severe PHN pain in the right thoracolumbar spine, right flank, and right lower abdomen showed poor responses to treatment with amitriptyline, gabapentin, and oxycodone/acetaminophen. However, a series of three thoracic transforaminal epidural steroid injections (TFESIs) effectively treated the PHN and achieved near-complete pain resolution. TFESI can be considered an early and first-choice treatment for PHN, but several courses may be required to achieve adequate and prolonged symptom control.

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.

The Safety and Effect of Local Botulinumtoxin A Injections for Long-Term Management of Chronic Pain in Post-Herpetic Neuralgia: Literature Review and Cases Report Treated with Incobotulinumtoxin A

There are few reports on the safety and effectiveness of long-term botulinumtoxin A (BoNT A) therapy in severe chronic pain of post-herpetic neuralgia (PHN). The literature was searched with the term "neuropathic pain" and "botulinum" on PubMed (up to 29 February 2020). Pain was assessed with the Visual Analogue Scale (VAS) before and after BoNT A therapy. A total of 10 clinical trials and six case reports including 251 patients with PHN were presented. They showed that BoNT A therapy had significant pain reduction (up to 30-50%) and improvement in quality of life. The effect duration seems to be correlated with BoNT A doses injected per injection site. Intervals between BoNT A injections were 10-14 weeks. No adverse events were reported in cases and clinical studies, even in the two pregnant women, whose babies were healthy. The repeated (≥6 times) intra/subcutaneous injections of incobotulinumtoxin A (Xeomin®, Merz Pharmaceuticals, Germany) over the two years of our three cases showed marked pain reduction and no adverse events. Adjunctive local BoNT A injection is a promising option for severe PHN, as a safe and effective therapy in long-term management for chronic neuropathic pain. Its effect size and -duration seem to be depended on the dose of BoNT A injected per each point.

The Mechanisms of Action of Botulinum Toxin Type A in Nociceptive and Neuropathic Pathways in Cancer Pain

BACKGROUND

Botulinum toxin type A (BoNT-A) is widely employed for cosmetic purposes and in the treatment of certain diseases such as strabismus, hemifacial spasm and focal dystonia among others. BoNT-A effect mainly acts at the muscular level by inhibiting the release of acetylcholine at presynaptic levels consequently blocking the action potential in the neuromuscular junction. Despite the great progress in approval and pharmaceutical usage, improvement in displacing BoNT-A to other pathologies has remained very limited. Patients under diagnosis of several types of cancer experience pain in a myriad of ways; it can be experienced as hyperalgesia or allodynia, and the severity of the pain depends, to some degree, on the place where the tumor is located. Pain relief in patients diagnosed with cancer is not always optimal, and as the disease progresses, transition to more aggressive drugs, like opioids is sometimes unavoidable. In recent years BoNT-A employment in cancer has been explored, as well as an antinociceptive drug; experiments in neuropathic, inflammatory and acute pain have been carried out in animal models and humans. Although its mechanism has not been fully known, evidence has shown that BoNT-A inhibits the secretion of pain mediators (substance P, Glutamate, and calcitonin gene related protein) from the nerve endings and dorsal root ganglion, impacting directly on the nociceptive transmission through the anterolateral and trigeminothalamic systems.

AIM

The study aimed to collect available literature regarding molecular, physiological and neurobiological evidence of BoNT-A in cancer patients suffering from acute, neuropathic and inflammatory pain in order to identify possible mechanisms of action in which the BoNT-A could impact positively in pain treatment.

CONCLUSION

BoNT-A could be an important neo-adjuvant and coadjuvant in the treatment of several types of cancer, to diminish pro-tumor activity and secondary pain.

Neuropathic pain: Spotlighting anatomy, experimental models, mechanisms, and therapeutic aspects

The International Association for the Study of Pain defines neuropathic pain as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system". The associated changes can be observed in the peripheral as well as the central nervous system. The available literature discusses a wide variety of causes as predisposing for the development and amplification of neuropathic pain. Further, key interactions within sensory pathways have been discovered, but no common molecular mechanism leading to neuropathic pain has been identified until now. In the first part of this review, the pain mediating lateral spinothalamic tract is described. Different in vivo models are presented that allow studying trauma-, chemotherapy-, virus-, and diabetes-induced neuropathic pain in rodents. We furthermore discuss approaches to assess neuropathic pain in these models. Second, the current knowledge about cellular and molecular mechanisms suggested to underlie the development of neuropathic pain is presented and discussed. A summary of established therapies that are already applied in the clinic and novel, promising approaches closes the paper. In conclusion, the established animal models are able to emulate the diversity of neuropathic pain observed in the clinics. However, the assessment of neuropathic pain in the presented in vivo models should be improved. The determination of common molecular markers with suitable in vitro models would simplify the assessment of neuropathic pain in vivo. This would furthermore provide insights into common molecular mechanisms of the disease and establish a basis to search for satisfying therapeutic approaches.

Efficacy of Dorsal Root Ganglion Pulsed Radiofrequency Combined with Paravertebral Injection of Recombinant Human Interferon-α2b in Herpetic Neuralgia

Objective

The purpose of this study was to investigate the clinical efficacy of dorsal root ganglion (DRG) pulsed radiofrequency combined with paravertebral injection of recombinant human interferon-α2b in the treatment of patients with acute herpes zoster neuralgia and its preventive effectiveness on postherpetic neuralgia (PHN).

Methods

A retrospective analysis of 62 patients with acute herpes zoster neuralgia was implemented. All patients were divided into two groups: pulsed radiofrequency paraspinal injection of recombinant human interferon-α2b (group P); pulsed radiofrequency combined with paravertebral injection of saline (group C). The numerical rating scales (NRS) scores were used for pain assessment, and the dose of the analgesic drug was recorded. Gal-3 and IL-6 levels in blood were compared between the two groups before treatment and at 1 week, 2, and 4 weeks after treatment. The incidence of PHN was recorded in both groups.

Results

The pain intensity, the levels of Gal-3 and IL-6 in blood and the dose of oral administration of gabapentin capsules and morphine were reduced in all patients after treatment. Compared with group C, patients in group P had lower NRS scores, blood levels of Gal-3 and IL-6, and dosages of oral gabapentin capsules and morphine hydrochloride immediate-release tablets after treatment. The incidence of PHN was significantly lower at 8 and 12 weeks.

Conclusion

DRG pulsed radiofrequency combined with paravertebral injection of recombinant human interferon-α2b for acute stage herpes zoster neuralgia is a more effective treatment, and can effectively prevent the incidence rate of PHN.

Therapeutic Use of Botulinum Neurotoxins in Dermatology: Systematic Review

Botulinum toxin is a superfamily of neurotoxins produced by the bacterium Clostridium Botulinum with well-established efficacy and safety profile in focal idiopathic hyperhidrosis. Recently, botulinum toxins have also been used in many other skin diseases, in off label regimen. The objective of this manuscript is to review and analyze the main therapeutic applications of botulinum toxins in skin diseases. A systematic review of the published data was conducted, following Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines. Botulinum toxins present several label and off-label indications of interest for dermatologists. The best-reported evidence concerns focal idiopathic hyperhidrosis, Raynaud phenomenon, suppurative hidradenitis, Hailey–Hailey disease, epidermolysis bullosa simplex Weber–Cockayne type, Darier’s disease, pachyonychia congenita, aquagenic keratoderma, alopecia, psoriasis, notalgia paresthetica, facial erythema and flushing, and oily skin. Further clinical trials are still needed to better understand the real efficacy and safety of these applications and to standardize injection and doses protocols for off label applications.

Alternative Clinical Indications of Botulinum Toxin

Botulinum toxin type A (BoNTA) is a powerful neurotoxin that inhibits acetylcholine release from presynaptic vesicles. The potency and safety profile of BoNTA grant the toxin vast therapeutic potential. It has been used off-label for a variety of dermatologic conditions. This review aims to analyze published literature regarding the benefits and risks of the off-label use of BoNTA beyond facial lines, including eccrine hidrocystomas, enlarged pores, keloids and hypertrophic scars, hidradenitis suppurativa, hyperhidrosis, masseter muscle hypertrophy, and salivary gland hypertrophy, among others. A MEDLINE search from January 2000 to December 2019 was conducted on the off-label uses of botulinum toxin in dermatology.

Efficacy of different interventions for the treatment of postherpetic neuralgia: a Bayesian network meta-analysis

OBJECTIVE

We aimed to perform a network meta-analysis that combined both direct and indirect evidence to compare the relative efficacy of interventional therapies to treat patients with postherpetic neuralgia (PHN) and to determine the treatments' superiority and validity.

METHOD

A conventional paired meta-analysis was performed. This was followed by a network meta-analysis using the Bayesian framework.

RESULTS

Botulinum toxin type A and pulsed radiofrequency (PRF) were the two most effective individual interventions. For combination therapy, PRF + nerve block (NB) was the best choice, followed by subcutaneous injection or local infiltration (SC) + NB + ozone (O3). However, the combination of PRF + NB + SC showed reduced the efficacy compared with each treatment and was highly invasive for patients. After a long-term follow-up, PRF was shown to be the most effective therapy for treating patients with PHN.

CONCLUSIONS

Regular anti-neuropathic drug administration that was accompanied by interventional therapies at an early stage is the best choice to treat patients with PHN. Appropriate combinations of different interventions show improved pain relief. Clinicians should manage therapeutic regimens on the basis of the patients specific condition and existing measures and strive to achieve personalized 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.

The effect of botulinum toxin A on patients with persistent idiopathic dentoalveolar pain-A systematic review

BACKGROUND

It has been suggested that botulinum toxin A (BONT-A) is a safe and effective treatment in relieving pain in patients with persistent idiopathic dentoalveolar pain (PIDP).

OBJECTIVES

This study aimed to systematically evaluate all the available studies investigating the pain-relieving effects of BONT-A in patients with PIDP.

METHODS

A systematic search with specific search terms was made in PubMed, Web of Science and Scopus. Two authors screened titles and abstracts and selected eligible studies for inclusion in the systematic review. The quality of the studies was evaluated by the 12 items Quality Assessment Tool for Observational studies (Pre-Post) Studies with No Control Group, and the level of evidence was assessed according to GRADE.

RESULTS

Three observational studies of 3695 identified were included (445 overlapping studies; 3247 excluded studies). All studies were uncontrolled observational studies investigating the pain-relieving effect of BONT-A in patients with PIDP. The included studies had a fair quality (moderate risk of bias) and insufficient level of evidence. The pain reducing effect by BONT-A injections was in average 50% or more in two studies, in one study 3 out of 4 patients became almost pain free.

CONCLUSIONS

This systematic review shows that presently the level of scientific evidence is insufficient to evaluate the pain-relieving effect of BONT-A injections in patients with PIDP. There are indications that BONT-A injections could be a possible management option for patients with PIDP that seems to be safe and with few adverse events. There is a need for well-designed placebo-controlled, double-blind RCTs.

Postherpetic Neuralgia: Current Evidence on the Topical Film-Forming Spray with Bupivacaine Hydrochloride and a Review of Available Treatment Strategies

PURPOSE OF REVIEW

This is a comprehensive review of the literature about the use of bupivacaine hydrochloride for the treatment of post-herpetic neuralgia (PHN). It briefly reviews the background, biology, diagnosis and conventional treatment for PHN, and then introduces and compares the recent evidence for the use of topical bupivacaine.

RECENT FINDINGS

PHN is defined by pain lasting 90 days or more after the initial presentation of herpes zoster ("Shingles", HZ) rash and is the most common complication of this disease. A product of re-activation of the Varicella-Zoster virus (VZV), HZ is diagnosed more than 1 million times annually in the United States. Approximately 20% of patients with HZ will experience PHN and will continue to suffer intermittent neuropathic symptoms, including itching and pain, that is sharp, stabbing, throbbing or burning, with the pain localized to the site of their original rash. This long-lasting pain compares with the severity of long-standing rheumatics and osteo-arthritis and is accompanied by severe allodynia causing significant suffering, and a financial burden that is manifested in both healthcare costs and loss of quality-adjusted life years. Prevention of PHN may be achieved with the Zoster vaccine, although there is still a large segment of unvaccinated population. Moreover, the Zoster vaccine is not always effective for prevention. Current treatment includes medical (systemic tricyclic antidepressants, anticonvulsants and opioids, topical lidocaine and capsaicin) and interventional (subcutaneous Botox injections, nerve blocks and nerve stimulation) therapies. These therapies are not always effective, and each carries their own profile of side effects and risks. Moreover, up to 50% of patients with PHN are refractory to management. Recent evidence is emerging to support the use of topical local anesthetics for the treatment of PHN. Two small studies recently found topical lidocaine spray to be effective in treating paroxysmal pain attacks associated with PHN. Bupivacaine is a longer-lasting local anesthetic, and a film-forming formulation allows easy and durable application to the affected skin. Recent studies show that topical film-forming bupivacaine is safe and as effective as lidocaine for the treatment of PHN. PHN is an important though common complication of HZ and can cause long-lasting pain and disability. Current treatment for PNH is limited by efficacy and safety profiles of individual therapies. Recent evidence points to topical local anesthetics as an effective and safe alternative to conventional therapy. Film-forming bupivacaine may offer a durable and safe option for this otherwise difficult to treat syndrome.

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.

Perineural injection of botulinum toxin-A in painful peripheral nerve injury - a case series: pain relief, safety, sensory profile and sample size recommendation

Objectives: Subcutaneous injection of botulinum toxin-A (sBONT-A) is a novel treatment for peripheral neuropathic pain. While its analgesic effects are well documented, this treatment is often not comfortable and fails in patients who show signs of sensory loss but rarely allodynia. There are some case reports about perineural BONT-A injection (pBONT-A) which could be an alternative approach. Here we present a retrospective, open label case series of pBONT-A's efficacy and safety regarding neurological consequences involving changes in somatosensory profiles of both responders and non-responders. Methods: Sixty patients (53 ± 13years, 77% males) with PNI were treated with pBONT-A after a test injection with a local anesthetic, which prompted distinctive pain relief. Quantitative sensory testing (QST; DFNS protocol) and pain intensity were assessed before and ≥7 days post pBONT-A injection. Definition of response: satisfactory pain reduction of ≥30% NRS (numerical rating scale: 0 = no pain, 10 = worst pain) for ≥4 days. Statistics: Paired t-test, Mann-Whitney U-test, χ² test. Results: A temporary weak paresis in one case was clinically verified. The QST -parameters remained unchanged, but patients with more frequent hyperalgesia signs reported less analgesia (p = .04). The pBONT-A injection prompted pain relief by 24.8% (NRS: 6.0 ± 1.7 vs. 4.5 ± 2.1; p < .0001); 57% (n = 34) were responders (NRS: 6.0 ± 1.6 vs. 3.4 ± 1.6, relief of 43.4%; p < .0001). Based on these results, we suggest that future parallel design trials on pBONT-A need to include at least 84 patients. Discussion: Ultrasound-guided pBONT-A injection seems to be a safe treatment leading to a sufficient pain relief for some months without sensory changes. Surprisingly, pBONT-A showed a pronounced analgesic effect also in patients without signs of hyperalgesia.

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.

Botulinum Toxin Type A for refractory trigeminal neuralgia in older patients: a better therapeutic effect

Background

Some studies have indicated that a local injection of Botulinum Toxin Type A (BTX-A) is a promising therapy for trigeminal neuralgia (TN). However, BTX-A treatment is still ineffective for approximately 10-43% of patients. We therefore investigated which factors are associated with the therapeutic effect in BTX-A treatment of medically refractory, classical TN.

Methods

We performed a retrospective cohort study with a total of 104 patients who were receiving BTX-A injection for medically refractory classical TN between August 2013 and October 2016. A VAS score, pain attack frequency per day as well as patients' overall response to treatment and side effects were evaluated in 104 patients with TN who were receiving BTX-A.

Results

A total of 87 patients reported successful results; 41 stated that their pain was completely controlled while 46 reported adequate pain relief, totaling 83.7%. Our study suggests that treatment success was higher in patients 50 or older (OR=3.66, 95% CI: 1.231-10.885). Univariate and multivariate analyses demonstrated that the patient's age was independently associated with treatment outcome (OR=1.72, 95% CI: 1.063-2.282), with ≥50 years being a significant predictor of pain relief (P=0.020 and P=0.033, respectively). Seventeen patients (16.3%) reported mild side effects.

Conclusion

A local injection of BTX-A may be a safe and efficient treatment for classical TN which lasts for several months. BTX-A is a novel strategy which is particularly worth trying for particularly middle-aged and elderly patients who cannot tolerate drug side effects and may be afraid of serious complications from microvascular decompression.

Eye Drop Instillation of the Rac1 Modulator CNF1 Attenuates Retinal Gliosis and Ameliorates Visual Performance in a Rat Model of Hypertensive Retinopathy

In hypertensive retinopathy, the retinal damage due to high blood pressure is accompanied by increased expression of Glial Fibrillary Acidic Protein (GFAP), which indicates a role of neuroinflammatory processes in such a retinopathy. Proteins belonging to the Rho GTPase family, particularly Rac1, are involved in the activation of Müller glia and in the progression of photoreceptor degeneration, and may thus represent a novel candidate for therapeutic intervention following central nervous system inflammation. In this paper, we have observed that topical administration as eye drops of Cytotoxic Necrotizing Factor 1 (CNF1), a Rho GTPase modulator, surprisingly improves electrophysiological and behavioral visual performances in aged spontaneously hypertensive rats. Furthermore, such functional improvement is accompanied by a reduction of Rac1 activity and retinal GFAP expression. Our results suggest that Rac1 inhibition through CNF1 topical administration may represent a new strategy to target retinal gliosis.

Emerging therapies in clinical development and new contributions for neuropathic pain

Neuropathic pain is very challenging to manage because of the heterogeneity of aetiologies, symptoms, and underlying mechanisms. Conventional oral therapies have been limited by negative factors such as systemic side effects, drug-drug interactions, slow onset of action, the need for titration, multiple daily dosing, as well as the potential risk of addiction, dependence, withdrawal symptoms and abuse. Therefore, new therapeutic perspectives are justified. New drugs that act on different therapeutic targets are currently in preclinical development or in their first phases of clinical development. In this review, focus will be directed specifically on new pharmacological treatments for neuropathic pain for which clinical data are already available, including older and known drugs with new data on their anti-neuropathic activity.