Relief of intractable pruritus after administration of botulinum toxin A (botox): a case report

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.

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.

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.

The non-neuronal and nonmuscular effects of botulinum toxin: an opportunity for a deadly molecule to treat disease in the skin and beyond

There is growing evidence that botulinum neurotoxins (BoNTs) exhibit biological effects on various human cell types with a host of associated clinical implications. This review aims to provide an update on the non-neuronal and nonmuscular effects of botulinum toxin. We critically analysed recent reports on the structure and function of cellular signalling systems subserving biological effects of BoNTs. The BoNT receptors and intracellular targets are not unique for neurotransmission. They have been found in both neuronal and non-neuronal cells, but there are differences in how BoNT binds to, and acts on, neuronal vs. non-neuronal cells. The non-neuronal cells that express one or more BoNT/A-binding proteins, and/or cleavage target synaptosomal-associated protein 25, include: epidermal keratinocytes; mesenchymal stem cells from subcutaneous adipose; nasal mucosal cells; urothelial cells; intestinal, prostate and alveolar epithelial cells; breast cell lines; neutrophils; and macrophages. Serotype BoNT/A can also elicit specific biological effects in dermal fibroblasts, sebocytes and vascular endothelial cells. Nontraditional applications of BoNT have been reported for the treatment of the following dermatological conditions: hyperhidrosis, Hailey-Hailey disease, Darier disease, inversed psoriasis, aquagenic palmoplantar keratoderma, pachyonychia congenita, multiple eccrine hydrocystomas, eccrine angiomatous hamartoma, eccrine sweat gland naevi, congenital eccrine naevus, Raynaud phenomenon and cutaneous leiomyomas. Experimental studies have demonstrated the ability of BoNT/A to protect skin flaps, facilitate wound healing, decrease thickness of hypertrophic scars, produce an anti-ageing effect, improve a mouse model of psoriasiform dermatitis, and have also revealed extracutaneous effects of BoNT arising from its anti-inflammatory and anticancer properties. BoNTs have a much wider range of applications than originally understood, and the individual cellular responses to the cholinergic impacts of BoNTs could provide fertile ground for future studies.

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.