Botulinum toxin type A for neuropathic itch

A systematic review of procedural modalities in the treatment of notalgia paresthetica

BACKGROUND

Notalgia paresthetica (NP) is a rare condition characterized by localized pain and pruritus of the upper back, associated with a distinct area of hyperpigmentation. Given the lack of standardized treatment and the uncertain efficacy of available options, applying procedural methods is of growing interest in treating NP.

AIMS

We sought to comprehensively evaluate the role of procedural treatments for NP.

METHODS

We systematically searched PubMed/Medline, Ovid Embase, and Web of Science until November 14th, 2023. We also performed a citation search to detect all relevant studies. Original clinical studies published in the English language were included.

RESULTS

Out of 243 articles, sixteen studies have reported various procedural modalities, with or without pharmacological components, in treating NP. Pharmacological procedures, including injections of botulinum toxin, lidocaine, and corticosteroids, led to a level of improvement in case reports and case series. However, botulinum toxin did not show acceptable results in a clinical trial. Moreover, non-pharmacological procedures were as follows: physical therapy, exercise therapy, kinesiotherapy, acupuncture and dry needling, electrical muscle stimulation, surgical decompression, and phototherapy. These treatments result in significant symptom control in refractory cases. Physical therapy can be considered a first-line choice or an alternative in refractory cases.

CONCLUSION

Procedural modalities are critical in the multidisciplinary approach to NP, especially for patients who are refractory to topical and oral treatments. Procedural modalities include a spectrum of options that can be applied based on the disease's symptoms and severity.

How Does Botulinum Toxin Inhibit Itch?

Two decades after reports of the anti-pruritic effects of botulinum neurotoxins (BoNTs), there is still no approved product for the anti-itch indication of BoNTs, and most clinical case reports still focus on the off-label use of BoNTs for various itchy conditions. Few randomized clinical trials have been conducted with controversial results, and the beneficial effects of BoNTs against itch are mainly based on case studies and case series. These studies are valuable in presenting the potential application of BoNTs in chronic pruritic conditions, but due to the nature of these studies, they are categorized as providing lower levels of evidence or lower grades of recommendation. To obtain approval for the anti-pruritic indication of BoNTs, higher levels of evidence are required, which can be achieved through conducting large-scale and well-designed studies with proper control groups and established careful and reliable primary and secondary outcomes. In addition to clinical evidence, presenting the mechanism-based antipruritic action of BoNTs can potentially strengthen, accelerate, and facilitate the current efforts towards further investments in accelerating the field towards the potential approval of BoNTs for itchy conditions. This review, therefore, aimed to provide the state-of-the-art mechanisms underlying the anti-itch effect of BoNTs from basic studies that resemble various clinical conditions with itch as a hallmark. Evidence of the neuronal, glial, and immune modulatory actions of BoNTs in reducing the transmission of itch are presented, and future potential directions are outlined.

Mechanisms and therapeutic targets for neuropathic itch

Neuropathic pruritus conditions arise from structural and/or functional damage of the peripheral or central nervous system. Novel findings of pruritus specific mediators and pathways strengthen the specificity theory of pruritus transmission, however electrophysiological studies suggest that focal activation of nociceptors and distinct discharge patterns of primary afferents also contribute to the development of the sensation of pruritus. A complex interplay between excitatory and inhibitory interneurons at spinal level, non-neuronal cells and descending modulation from upper centers contributes to neuronal sensitization and clinically to the chronicity of pruritus, as well as accompanying phenomena such as alloknesis and hyperknesis. Several topical, systemic and non-pharmacological therapeutic approaches directed at distinct targets are currently available.

Botulinum toxin type A therapy for bilateral focal neuropathic pruritus in multiple sclerosis: a case report

Neuropathic pruritus is a form of chronic itch that occurs in the presence of direct damage to the nervous system. It tends to be severe, disabling, and difficult to treat. Usual antipruritic medications are largely ineffective and there is no consensus regarding the treatment approach. The authors report a case of a 58-year-old man with primary progressive multiple sclerosis and a history of unsatisfactory management of severe bilateral focal pruritus. Significant symptom relief was attained after local intradermal injections of botulinum toxin type A.

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.

Neuropathic Itch

Neurologic insults as varied as inflammation, stroke, and fibromyalgia elicit neuropathic pain and itch. Noxious sensation results when aberrantly increased afferent signaling reaches percept-forming cortical neurons and can occur due to increased sensory signaling, decreased inhibitory signaling, or a combination of both processes. To treat these symptoms, detailed knowledge of sensory transmission, from innervated end organ to cortex, is required. Molecular, genetic, and behavioral dissection of itch in animals and patients has improved understanding of the receptors, cells, and circuits involved. In this review, we will discuss neuropathic itch with a focus on the itch-specific circuit.

Post-Burn Pruritus

Post-burn pruritus is the pruritus that occurs after burn during the rehabilitation and healing process of burn wounds. The post-burn pruritus is a common and serious complication of burn injury, which severely lowers the quality of life of the patient. Many potential treatments are available for pruritus but there is no consensus of the best single treatment yet. The precise mechanism of post-burn pruritus has not been elucidated, but it appears to have pruritogenic and neuropathic aspects. Clinically, post-burn pruritus tends to be intractable to conventional treatment but rather responds to neuroleptic agents, such as gabapentin and pregabalin. During wound healing, various neuropeptides secreted from the nerves of the skin control epidermal and vascular proliferation and connective tissue cells. When keratinocytes are activated by an itch-inducing substance, they secrete a variety of inflammatory substances that increase the susceptibility of the itch receptor. There are two mechanisms underlying post-burn neuropathic pruritus. The first one is peripheral sensitization. The second one is the intact nociceptor hypothesis. An effective treatment for post-burn pruritus will also be effective in other neuropathic and intractable itching. In this review, we summarized the interaction and mechanism of keratinocytes, immune cells, and nerve fibers related to post-burn pruritus.

Interventions in the B-type natriuretic peptide signalling pathway as a means of controlling chronic itch

Chronic itch poses major health care and economic burdens worldwide. In 2013, B-type natriuretic peptide (BNP) was identified as an itch-selective neuropeptide and shown to be both necessary and sufficient to produce itch behaviour in mice. Since then, mechanistic studies of itch have increased, not only at central levels of the spinal relay of itch signalling but also in the periphery and skin. In this review, we have critically analysed recent findings from complementary pharmacological and physiological approaches, combined with genetic strategies to examine the role of BNP in itch transduction and modulation of other pruritic proteins. Additionally, potential targets and possible strategies against BNP signalling are discussed for developing novel therapeutics in itch. Overall, we aim to provide insights into drug development by altering BNP signalling to modulate disease symptoms in chronic itch, including conditions for which no approved treatment exists.

Chronic itch management: therapies beyond those targeting the immune system

OBJECTIVE

Chronic itch can be a debilitating, unrelenting symptom. Over the years, we have advanced our knowledge about immune-mediated itch (eg, atopic dermatitis) and have developed several treatments targeting these immune pathways. Chronic itch that is noninflammatory in nature is more elusive. However, we have gained some understanding of the neural component mediating itch and have made progress in treating this challenging symptom.

DATA SOURCES

A comprehensive literature search was conducted, and data and literature were reviewed on the topics of chronic itch, its pathophysiology, and nonimmunological treatments for chronic itch that work on the nerves.

STUDY SELECTIONS

Basic science papers, review articles, case reports, and clinical trial data were considered.

RESULTS

A variety of topical and systemic therapies targeting the nerves have shown effectiveness in treating patients with chronic itch of different types.

CONCLUSION

Treating chronic itch may be challenging, but an arsenal of treatments are available and many are on the horizon as we expand our knowledge of mechanisms of itch and the neural receptors involved.

Antipruritic Effects of Botulinum Neurotoxins

This review explores current evidence to demonstrate that botulinum neurotoxins (BoNTs) exert antipruritic effects. Both experimental and clinical conditions in which botulinum neurotoxins have been applied for pruritus relief will be presented and significant findings will be highlighted. Potential mechanisms underlying antipruritic effects will also be discussed and ongoing challenges and unmet needs will be addressed.

Botulinum Toxin Off-Label Use in Dermatology: A Review

BACKGROUND

Botulinum toxin is a neurotoxin produced by the bacterium Clostridium botulinum which causes a flaccid muscle paralysis. It is currently used for aesthetic treatments and in the focal hyperhidrosis. Recently, botulinum toxin has also been used experimentally in many other dermatological conditions with good results.

OBJECTIVE

To review and analyze the possible botulinum toxin off-label applications published.

METHODS

A retrospective review of the published data was conducted.

CONCLUSIONS

this potent drug can lead to several off-label indications of interest for dermatologists. Further clinical trials are still needed to better understand the real efficacy and safety of these applications and to standardize injection and dose protocols.

Neuropathic pruritus

Pruritus, also known as itch, is a very common, unpleasant sensation that elicits an urge to scratch. Its origin is not always in the skin, and neuropathic itch that is caused by neuronal or glial damage is common, but poorly understood by both dermatologists and neurologists. Although pruritus has not been considered as serious a symptom as pain, it is difficult to treat and--if chronic--can severely impair quality of life. Neuropathic itch is often associated with other clinical symptoms, most commonly neuropathic pain, and hypersensitization to stimuli is present in both pruritus and pain of neuropathic origin. The shared aetiology can aid in finding suitable treatment for itch in some cases, but more detailed knowledge of the mechanisms of itch, along with standardized, well-controlled trials, is needed. Pruritus research is an emerging but currently very active field, and our understanding of this sensation is rapidly increasing. Here, we review new discoveries regarding the role of the nervous system and the contribution of different pathways in pruritus, discuss the different aetiologies of neuropathic itch, and outline currently available and potential strategies for managing neuropathic pruritus.

Notalgia paresthetica: treatment using intradermal botulinum toxin A

INTRODUCTION

Notalgia paresthetica is a sensory mononeuropathy that affects dorsal segments T2 to T6. It can have a significant effect on quality of life. Numerous treatments have been used with variable results.

MATERIAL AND METHODS

Five patients diagnosed with notalgia paresthetica were treated with intradermal botulinum toxin A. None had achieved relief of the pruritus with previous treatments.

RESULTS

Variable results were observed after the administration of intradermal botulinum toxin. Complete resolution of the pruritus was not achieved in any of the patients.

CONCLUSIONS

Botulinum toxin A appears to be a safe therapeutic option for patients with notalgia paresthetica. However, data currently available come from small patient series, making it difficult to draw definitive conclusions regarding the true efficacy and long-term effects of this treatment.

The neurology of itch

Research over the past 15 years has helped to clarify the anatomy and physiology of itch, the clinical features of neuropathic itch syndromes and the scientific underpinning of effective treatments. Two itch-sensitive pathways exist: a histamine-stimulated pathway that uses mechanically insensitive C-fibres, and a cowhage-stimulated pathway primarily involving polymodal C-fibres. Interactions with pain continue to be central to explaining various aspects of itch. Certain spinal interneurons (Bhlhb5) inhibit itch pathways within the dorsal horn; they may represent mediators between noxious and pruritic pathways, and allow scratch to inhibit itch. In the brain, functional imaging studies reveal diffuse activation maps for itch that overlap, but not identically, with pain maps. Neuropathic itch syndromes are chronic itch states due to dysfunction of peripheral or central nervous system structures. The most recognized are postherpetic itch, brachioradial pruritus, trigeminal trophic syndrome, and ischaemic stroke-related itch. These disorders affect a patient's quality of life to a similar extent as neuropathic pain. Treatment of neuropathic itch focuses on behavioural interventions (e.g., skin protection) followed by stepwise trials of topical agents (e.g., capsaicin), antiepileptic drugs (e.g., gabapentin), injection of other agents (e.g., botulinum A toxin), and neurostimulation techniques (e.g., cutaneous field stimulation). The involved mechanisms of action include desensitization of nerve fibres (in the case of capsaicin) and postsynaptic blockade of calcium channels (for gabapentin). In the future, particular histamine receptors, protease pathway molecules, and vanilloids may serve as targets for novel antipruritic agents.

Intralesional therapy for psoriasis

Localized resistant plaques of psoriasis often remain despite highly effective anti-psoriasis treatment. Intralesional therapy is often used to treat various malignant, infectious or inflammatory cutaneous diseases, including psoriasis. Despite the presence of many review articles on the treatment of psoriasis, no articles exist which review the use of intralesional therapy for psoriasis. In this article, we review the published literatures of intralesional therapy for psoriasis. Corticosteroids, methotrexate, cyclosporin, biologics, botulinum toxin type-A, 15-hydroxyeicosatetraenoic acid, and chemotherapy agents such as 5-fluorouracil are discussed. Also, agents which may be used intralesionally and have the potential to treat psoriasis will also be reviewed such as bleomycin, vincristine or vinblastine, mitomycin-C, aminophylline, 5-aminolevulinic acid, rituximab, bevacizumab and pentoxifylline are included.

Targeted treatment of pruritus: a look into the future

Recent advances in pruritus research have elucidated mediators and neuronal pathways involved in itch transmission, and this fast emerging knowledge may possibly be translated into new therapies in the near future. In the skin and peripheral nerves, potential mediator and receptor therapeutic targets include the H4 histamine receptor, protease-activated receptor 2, serine proteases, cathepsin S, peripheral mu- and kappa-opioid receptors, interleukin-31, transient receptor potential vanilloid 1 and 3, fatty acid amide hydrolase, nerve growth factor and its receptor, acetylcholine, and the Mas-related G protein-coupled receptors. In the spinal cord, gastrin-related peptide and its receptor, as well as substance P and its receptor neurokinin receptor-1 serve as potential therapeutic targets. In the brain, reduction of itch perception and modulation of emotions may possibly be achieved through drugs acting on the anterior cingulate cortex. Clinically, management of pruritus should be instituted early and should address the skin pathology, peripheral neuropathy, central sensitization, and the cognito-affective aspects of the disease.

Targeted treatment of pruritus: a look into the future

Recent advances in pruritus research have elucidated mediators and neuronal pathways involved in itch transmission, and this fast emerging knowledge may possibly be translated into new therapies in the near future. In the skin and peripheral nerves, potential mediator and receptor therapeutic targets include the H4 histamine receptor, protease-activated receptor 2, serine proteases, cathepsin S, peripheral mu- and kappa-opioid receptors, interleukin-31, transient receptor potential vanilloid 1 and 3, fatty acid amide hydrolase, nerve growth factor and its receptor, acetylcholine, and the Mas-related G protein-coupled receptors. In the spinal cord, gastrin-related peptide and its receptor, as well as substance P and its receptor neurokinin receptor-1 serve as potential therapeutic targets. In the brain, reduction of itch perception and modulation of emotions may possibly be achieved through drugs acting on the anterior cingulate cortex. Clinically, management of pruritus should be instituted early and should address the skin pathology, peripheral neuropathy, central sensitization, and the cognito-affective aspects of the disease.