Clinical practice. Chronic pruritus

Topically Applied Therapies for the Treatment of Skin Disease: Past, Present, and Future

The purpose of this review is to summarize essential biological, pharmaceutical, and clinical aspects in the field of topically applied medicines that may help scientists when trying to develop new topical medicines. After a brief history of topical drug delivery, a review of the structure and function of the skin and routes of drug absorption and their limitations is provided. The most prevalent diseases and current topical treatment approaches are then detailed, the organization of which reflects the key disease categories of autoimmune and inflammatory diseases, microbial infections, skin cancers, and genetic skin diseases. The complexity of topical product development through to large-scale manufacturing along with recommended risk mitigation approaches are then highlighted. As such topical treatments are applied externally, patient preferences along with the challenges they invoke are then described, and finally the future of this field of drug delivery is discussed, with an emphasis on areas that are more likely to yield significant improvements over the topical medicines in current use or would expand the range of medicines and diseases treatable by this route of administration. SIGNIFICANCE STATEMENT: This review of the key aspects of the skin and its associated diseases and current treatments along with the intricacies of topical formulation development should be helpful in making judicious decisions about the development of new or improved topical medicines. These aspects include the choices of the active ingredients, formulations, the target patient population's preferences, limitations, and the future with regard to new skin diseases and topical medicine approaches.

Interventions for postburn pruritus

BACKGROUND

Postburn pruritus (itch) is a common and distressing symptom experienced on healing or healed burn or donor site wounds. Topical, systemic, and physical treatments are available to control postburn pruritus; however, it remains unclear how effective these are.

OBJECTIVES

To assess the effects of interventions for treating postburn pruritus in any care setting.

SEARCH METHODS

In September 2022, we searched the Cochrane Wounds Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), Ovid MEDLINE (including In-Process & Other Non-Indexed Citations), Ovid Embase, and EBSCO CINAHL Plus. We also searched clinical trials registries and scanned references of relevant publications to identify eligible trials. There were no restrictions with respect to language, publication date, or study setting.

SELECTION CRITERIA

Randomised controlled trials (RCTs) that enrolled people with postburn pruritus to compare an intervention for postburn pruritus with any other intervention, placebo or sham intervention, or no intervention.

DATA COLLECTION AND ANALYSIS

We used the standard methodological procedures expected by Cochrane. We used GRADE to assess the certainty of the evidence.

MAIN RESULTS

We included 25 RCTs assessing 21 interventions with 1166 randomised participants. These 21 interventions can be grouped into six categories: neuromodulatory agents (such as doxepin, gabapentin, pregabalin, ondansetron), topical therapies (such as CQ-01 hydrogel, silicone gel, enalapril ointment, Provase moisturiser, beeswax and herbal oil cream), physical modalities (such as massage therapy, therapeutic touch, extracorporeal shock wave therapy, enhanced education about silicone gel sheeting), laser scar revision (pulsed dye laser, pulsed high-intensity laser, fractional CO2 laser), electrical stimulation (transcutaneous electrical nerve stimulation, transcranial direct current stimulation), and other therapies (cetirizine/cimetidine combination, lemon balm tea). Most RCTs were conducted at academic hospitals and were at a high risk of performance, attrition, and detection bias. While 24 out of 25 included studies reported change in burn-related pruritus, secondary outcomes such as cost-effectiveness, pain, patient perception, wound healing, and participant health-related quality of life were not reported or were reported incompletely. Neuromodulatory agents versus antihistamines or placebo There is low-certainty evidence that doxepin cream may reduce burn-related pruritus compared with oral antihistamine (mean difference (MD) -2.60 on a 0 to 10 visual analogue scale (VAS), 95% confidence interval (CI) -3.79 to -1.42; 2 studies, 49 participants). A change of 2 points represents a minimal clinically important difference (MCID). Due to very low-certainty evidence, it is uncertain whether doxepin cream impacts the incidence of somnolence as an adverse event compared to oral antihistamine (risk ratio (RR) 0.64, 95% CI 0.32 to 1.25; 1 study, 24 participants). No data were reported on pain in the included study. There is low-certainty evidence that gabapentin may reduce burn-related pruritus compared with cetirizine (MD -2.40 VAS, 95% CI -4.14 to -0.66; 1 study, 40 participants). A change of 2 points represents a MCID. There is low-certainty evidence that gabapentin reduces the incidence of somnolence compared to cetirizine (RR 0.02, 95% CI 0.00 to 0.38; 1 study, 40 participants). No data were reported on pain in the included study. There is low-certainty evidence that pregabalin may result in a reduction in burn-related pruritus intensity compared with cetirizine with pheniramine maleate (MD -0.80 VAS, 95% CI -1.24 to -0.36; 1 study, 40 participants). A change of 2 points represents a MCID. There is low-certainty evidence that pregabalin reduces the incidence of somnolence compared to cetirizine (RR 0.04, 95% CI 0.00 to 0.69; 1 study, 40 participants). No data were reported on pain in the included study. There is moderate-certainty evidence that ondansetron probably results in a reduction in burn-related pruritus intensity compared with diphenhydramine (MD -0.76 on a 0 to 10 numeric analogue scale (NAS), 95% CI -1.50 to -0.02; 1 study, 38 participants). A change of 2 points represents a MCID. No data were reported on pain and adverse events in the included study. Topical therapies versus relevant comparators There is moderate-certainty evidence that enalapril ointment probably decreases mean burn-related pruritus compared with placebo control (MD -0.70 on a 0 to 4 scoring table for itching, 95% CI -1.04 to -0.36; 1 study, 60 participants). No data were reported on pain and adverse events in the included study. Physical modalities versus relevant comparators Compared with standard care, there is low-certainty evidence that massage may reduce burn-related pruritus (standardised mean difference (SMD) -0.86, 95% CI -1.45 to -0.27; 2 studies, 166 participants) and pain (SMD -1.32, 95% CI -1.66 to -0.98). These SMDs equate to a 4.60-point reduction in pruritus and a 3.74-point reduction in pain on a 10-point VAS. A change of 2 VAS points in itch represents a MCID. No data were reported on adverse events in the included studies. There is low-certainty evidence that extracorporeal shock wave therapy (ESWT) may reduce burn-related pruritus compared with sham stimulation (SMD -1.20, 95% CI -1.65 to -0.75; 2 studies, 91 participants). This equates to a 5.93-point reduction in pruritus on a 22-point 12-item Pruritus Severity Scale. There is low-certainty evidence that ESWT may reduce pain compared with sham stimulation (MD 2.96 on a 0 to 25 pressure pain threshold (PPT), 95% CI 1.76 to 4.16; 1 study, 45 participants). No data were reported on adverse events in the included studies. Laser scar revision versus untreated or placebo controls There is moderate-certainty evidence that pulsed high-intensity laser probably results in a reduction in burn-related pruritus intensity compared with placebo laser (MD -0.51 on a 0 to 1 Itch Severity Scale (ISS), 95% CI -0.64 to -0.38; 1 study, 49 participants). There is moderate-certainty evidence that pulsed high-intensity laser probably reduces pain compared with placebo laser (MD -3.23 VAS, 95% CI -5.41 to -1.05; 1 study, 49 participants). No data were reported on adverse events in the included studies.

AUTHORS' CONCLUSIONS

There is moderate to low-certainty evidence on the effects of 21 interventions. Most studies were small and at a high risk of bias related to blinding and incomplete outcome data. Where there is moderate-certainty evidence, practitioners should consider the applicability of the evidence for their patients.

Increased Systemic Levels of Centrally Acting B-Type Natriuretic Peptide Are Associated with Chronic Itch of Different Types

B-type natriuretic peptide (BNP) is an itch-selective neuropeptide that was shown to play a role in both histaminergic and nonhistaminergic itch in mice. It was also shown that elevated serum BNP is linked to increased pruritus in nondiabetic hemodialysis patients. This study examined plasma BNP levels of 77 patients and N-terminal pro-BNP levels of 33 patients with differing types of chronic itch to see whether BNP and N-terminal pro-BNP levels can correlate with itch severity. Plasma BNP and N-terminal pro-BNP levels of all patients with itch correlated with itch numerical rating scale and in particular for patients with chronic pruritus of unknown origin. On the basis of this clinical observation, this study further showed that increasing pathophysiological levels of BNP in mice by intravenous or osmotic pump induced significant scratching. In addition, pharmacological and ablation strategies determined that BNP acts centrally by activating the natriuretic peptide receptor A in the dorsal horn of the spinal cord. These data support that BNP and N-terminal pro-BNP levels are associated with chronic itch and may be used in clinical setting.

Mechanisms and treatment of opioid-induced pruritus: Peripheral and central pathways

BACKGROUND AND OBJECTIVE

Pruritus (also known as itch) is defined as an unpleasant and irritating sensation of the skin that provokes an urge to scratch or rub. It is well known that opioid administration can cause pruritus, which is paradoxical as itch and pain share overlapping sensory pathways. Because opioids inhibit pain but can cause itching. Significant progress has been made to improve our understanding of the fundamental neurobiology of itch; however, much remains unknown about the mechanisms of opioid-induced pruritus. The prevention and treatment of opioid-induced pruritus remains a challenge in the field of pain management. The objective of this narrative review is to present and discuss the current body of literature and summarize the current understanding of the mechanisms underlying opioid-induced pruritus, and its relationship to analgesia, and possible treatment options.

RESULTS

The incidence of opioid-induced pruritus differs with different opioids and routes of administration, and the various mechanisms can be broadly divided into peripheral and central. Especially central mechanisms are intricate, even at the level of the spinal dorsal horn. There is evidence that opioid receptor antagonists and mixed agonist and antagonists, especially μ-opioid antagonists and κ-opioid agonists, are effective in relieving opioid-induced pruritus. Various treatments have been used for opioid-induced pruritus; however, most of them are controversial and have conflicting results.

CONCLUSION

The use of a multimodal analgesic treatment regimen combined with a mixed antagonist and κ agonists, especially μ-opioid antagonists, and κ-opioid agonists, seems to be the current best treatment modality for the management of opioid-induced pruritus and pain.

SIGNIFICANCE

Opioids remain the gold standard for the treatment of moderate to severe acute pain as well as cancer pain. It is well known that opioid-induced pruritus often does not respond to regular antipruritic treatment, thereby posing a challenge to clinicians in the field of pain management. We believe that our review makes a significant contribution to the literature, as studies on the mechanisms of opioid-induced pruritus and effective management strategies are crucial for the management of these patients.

Virtual reality used to distract children and young people with long-term conditions from pain or pruritus: A scoping review using PAGER

AIMS AND OBJECTIVES

To map out the primary research studies relating to how virtual reality (VR) has been used to distract children and young people with long-term conditions from pain or pruritus.

BACKGROUND

Pharmacologic treatment of chronic pain and pruritus may have side effects; hence, non-invasive non-pharmacological treatments are being sought.

DESIGN

The scoping review followed the methodology recommended by the Joanna Briggs Institute, PAGER framework and PRISMA-ScR checklist. The protocol was registered with the Open Science Registration on 14 February 2022 https//doi.org/10.17605/OSF.IO/K2R93.

METHODS

Five databases (Medline, CINAHL, PsycINFO, Web of Science and Scopus) were searched. Data were extracted from primary research studies published between 2000 and 2022 involving children and adolescent populations (<21 years) with a long-term condition that had an element of enduring pruritus and/or pain.

RESULTS

Of 464 abstracts screened, 35 full-text papers were assessed with 5 studies meeting the eligibility criteria. Three main themes emerged from the included studies: (1) Improvements in pain and daily functioning; (2) positive perceptions of VR and (3) accessibility and feasibility of VR. No papers were found on the effect of VR on alleviating pruritus.

CONCLUSION

VR is feasible, acceptable, and safe for children and adolescents with chronic pain in a range of long-term conditions and offers promise as an adjunctive treatment for improving chronic pain and quality of life. No studies were identified that targeted pruritis or measured pruritis outcomes; thus, the effects of VR for pruritis are unknown. There is a need for rigorously designed, randomised controlled trials to test the clinical and cost-effectiveness of VR interventions for chronic pain and pruritis in children and adolescents. The use of the PAGER (Patterns, Advances, Gaps, Evidence for Practice and Research Recommendations) framework for scoping reviews helped to structure analysis and findings and identify research gaps.

RELEVANCE TO CLINICAL PRACTICE

VR interventions offer promise in improving chronic pain related to long-term conditions.

The G protein-coupled estrogen receptor of the trigeminal ganglion regulates acute and chronic itch in mice

AIMS

Itch is an unpleasant sensation that severely impacts the patient's quality of life. Recent studies revealed that the G protein-coupled estrogen receptor (GPER) may play a crucial role in the regulation of pain and itch perception. However, the contribution of the GPER in primary sensory neurons to the regulation of itch perception remains elusive. This study aimed to investigate whether and how the GPER participates in the regulation of itch perception in the trigeminal ganglion (TG).

METHODS AND RESULTS

Immunofluorescence staining results showed that GPER-positive (GPER+ ) neurons of the TG were activated in both acute and chronic itch. Behavioral data indicated that the chemogenetic activation of GPER+ neurons of the TG of Gper-Cre mice abrogated scratching behaviors evoked by acute and chronic itch. Conversely, the chemogenetic inhibition of GPER+ neurons resulted in increased itch responses. Furthermore, the GPER expression and function were both upregulated in the TG of the dry skin-induced chronic itch mouse model. Pharmacological inhibition of GPER (or Gper deficiency) markedly increased acute and chronic itch-related scratching behaviors in mouse. Calcium imaging assays further revealed that Gper deficiency in TG neurons led to a marked increase in the calcium responses evoked by agonists of the transient receptor potential ankyrin A1 (TRPA1) and transient receptor potential vanilloid V1 (TRPV1).

CONCLUSION

Our findings demonstrated that the GPER of TG neurons is involved in the regulation of acute and chronic itch perception, by modulating the function of TRPA1 and TRPV1. This study provides new insights into peripheral itch sensory signal processing mechanisms and offers new targets for future clinical antipruritic therapy.

Consensus document on palliative care in cardiorenal patients

There is an unmet need to create consensus documents on the management of cardiorenal patients since, due to the aging of the population and the rise of both pathologies, these patients are becoming more prevalent in daily clinical practice. Chronic kidney disease coexists in up to 40%-50% of patients with chronic heart failure cases. There have yet to be consensus documents on how to approach palliative care in cardiorenal patients. There are guidelines for patients with heart failure and chronic kidney disease separately, but they do not specifically address patients with concomitant heart failure and kidney disease. For this reason, our document includes experts from different specialties, who will not only address the justification of palliative care in cardiorenal patients but also how to identify this patient profile, the shared planning of their care, as well as knowledge of their trajectory and the palliative patient management both in the drugs that will help us control symptoms and in advanced measures. Dialysis and its different types will also be addressed, as palliative measures and when the decision to continue or not perform them could be considered. Finally, the psychosocial approach and adapted pharmacotherapy will be discussed.

Gabapentin and oral antidepressants for chronic pruritus: a prospective cohort study evaluating efficacy and side effects in daily dermatological practice

BACKGROUND

Chronic pruritus is frequently seen in daily dermatological practice and is associated with marked impact on quality of life. Research on the use of gabapentin and oral antidepressants in daily dermatological practice is scarce.

OBJECTIVE

To evaluate the efficacy and safety of gabapentin and oral antidepressants in patients with chronic pruritus in daily clinical practice.

METHODS

A prospective observational single-center cohort study was conducted including adult patients with chronic pruritus and an indication for systemic treatment between June 2016 and May 2019.

RESULTS

Systemic treatment with gabapentin and/or antidepressants was initiated in 31 patients with severe chronic pruritus (median average pruritus NRS score 7.0), in which most cases no underlying origin was identified (83.9%). In patients treated with gabapentin 900-1800 mg/day (N = 25), median average pruritus NRS decreased to 5.5 (IQR 3.0) after 4 weeks and remained stable up to 24 weeks of treatment. Efficacy of antidepressants was variable, with the highest response after initiation of amitriptyline, nortriptyline, and mirtazapine. Side effects were frequently observed in both gabapentin and antidepressant treatments; however, were mostly mild and temporary.

LIMITATIONS

This was a single-site observational study, with limited sample size.

CONCLUSION

Treatment with gabapentin and antidepressants should be considered in patients with chronic pruritus unresponsive to conventional treatment.

Effects of oral morphine on experimentally evoked itch and pain: a randomized, double-blind, placebo-controlled trial

OBJECTIVES

Pain and itch share similar neuronal networks; hence, it is difficult to explain why opioids can relieve pain but provoke itching. The present human volunteer study aimed to investigate the similarities and differences in responses to experimentally provoked pain and itching to explore the underlying fundamental mechanisms.

METHODS

Twenty-four healthy volunteers were enrolled in this single-center, randomized, double-blind, placebo-controlled, parallel-group trial. Three volar forearms and two mandibular areas were marked, and participants randomly received morphine (20 mg) or identical placebo tablets. Heat, cold, and pressure pain thresholds, and vasomotor responses were assessed at baseline and after oral morphine administration. Itch provocations were induced by intradermal application of 1 % histamine or a topical cowhage (non-histaminergic itch) to a marked area of the skin. The participants were subsequently asked to rate their itching and pain intensities. The assessments were repeated for all marked areas.

RESULTS

Morphine caused analgesia, as assessed by the significant modulation of cold and pressure pain thresholds (p<0.05). There were no significant differences in histaminergic or non-histaminergic itch or pain intensity between the morphine and placebo groups. Superficial blood perfusion (vasomotor response) following histamine provocation was significantly increased by morphine (p<0.05) in both areas. No correlation was found between the provoked itch intensity and analgesic efficacy in any area or group.

CONCLUSIONS

Oral administration of morphine caused analgesia without modulating itch intensities but increased neurogenic inflammation in response to histamine, suggesting that different opioid mechanisms in histaminergic and non-histaminergic neurons evoke neurogenic inflammation.

Scratching increases epidermal neuronal branching and alters psychophysical testing responses in atopic dermatitis and brachioradial pruritus

Background

Chronic scratching imposes a major stress on the skin and can lead to itch intensity worsening, and consequently, patients may enter an itch-scratch cycle. This repetitive mechanical stress can result in lichenification, worsening of epidermal barrier function, and enhanced cutaneous inflammation. Furthermore, a reduction of intraepidermal nerve fibers was previously described in lichenification.

Aim

The aim of this study was to investigate the influence of chronic scratching on the epidermal neuroanatomy and on sensory changes, in particular the prevalence of hyperknesis and alloknesis in patients after mechanical, chemical, and electrical stimuli.

Methods

Analyses were performed on pruritic lichenified (chronically scratched), pruritic non-lichenified (not chronically scratched), and non-pruritic non-lesional (unaffected) skin areas of patients with inflammatory pruritus, i.e., atopic dermatitis (n = 35), and neuropathic pruritus, i.e., brachioradial pruritus (n = 34) vs. healthy matched controls (n = 64). Our fine-grained spatial skin characterization enabled specifically studying the differential effects of chronic scratching in inflammatory and neuropathic itch.

Results

Analysis of intraepidermal nerve fiber density showed rarefaction of fibers in all three skin areas of patients compared with healthy controls in both diagnoses. Even more, the two pruritic areas had significantly less nerve fibers than the unaffected skin, whereas electrically induced itch was massively increased. Epidermal branching of the remaining nerve fibers in lichenified/chronically scratched skin was increased, particularly in patients with brachioradial pruritus, which may contribute to the pronounced local neuronal sensitivity. Hyperknesis and alloknesis were found to increase independently of lichenification.

Conclusion

Our results indicate that chronic scratching may not affect intraepidermal nerve fiber density but leads to a stronger branching pattern of intraepidermal nerve fibers, which may contribute to local hypersensitivity. The increased sensitivity in the pruritic areas suggests mechanisms of peripheral sensitization, whereas the increased sensation of electrically and chemically induced itch in unaffected skin indicates central sensitization for itch.

Prolonged Antipruritic Effect of Botulinum Toxin Type A on Cowhage-induced Itch: A Randomized, Single-blind, Placebo-controlled Trial

Botulinum toxin type A (Botox) is thought to have antipruritic effects through inhibition of pruritic factors, including acetylcholine, substance P, and glutamate. The aim of this randomized, single-blind, placebo-controlled trial was to test the effect of botulinum toxin type A on cowhage, a non-histaminergic model for chronic itch. Botulinum toxin type A was injected into the arm of 35 healthy subjects, with a saline control injected into the contralateral arm. Thermal sensory parameters (warmth and heat thresholds and heat pain intensity) and itch intensity after cowhage application were examined on test areas. Botulinum toxin type A reduced itch intensity, overall perceived itch (area under the curve (AUC); percentage change from baseline), and peak itch intensity compared with the control at 1 week, 1 month, and 3 months. Botulinum toxin type A had no effect on thermal thresholds or heat pain intensity. In conclusion, botulinum toxin type A reduced cowhage itch for at least 3 months, which suggests that botulinum toxin type A is a potential long-lasting treatment for localized, non-histaminergic itch.

Prevalence of Chronic Pruritus in Elderly Black and White Inpatients: A Comparative Population Study

BACKGROUND

Black and geriatric patients were reported in small scale studies to have more intense chronic pruritus (CP). Studies comparing itch across geriatric racial groups are lacking.

OBJECTIVES

To compare the prevalence of CP in Black and White inpatients ≥ 65 years old as well as the top primary diagnoses of these populations.

METHODS

We used data from the National Inpatient Sample from 2016-2019 to analyze CP prevalence and ICD10-CM to identify diseases. The top five primary diagnoses were calculated for a subpopulation with CP. Sample characteristics were described, and the data was pooled and analyzed using IBM SPSS® Complex Sample modules.

RESULTS

Among hospitalized Black inpatients ≥ 65 years old, the prevalence of CP was 0.26% while in the White cohort it was 0.22%. The top five primary diagnoses in the Black population with itch were sepsis (4.2%); hypertensive heart and chronic kidney disease (CKD) with heart failure (HF) and stage 1-4 CKD, or unspecified CKD (4.1%); acute kidney failure (4.0%); hypertensive heart and CKD with HF with stage 5 CKD, or end-stage renal disease (2.1%); and hypertensive heart disease with HF (1.7%). The top five primary diagnoses in the White population were sepsis (4.25%); acute kidney failure (3.0%); hypertensive heart and CKD with HF and stage 1-4 CKD, or unspecified CKD (2.5%); cellulitis of left lower limb (1.9%); and unilateral primary osteoarthritis, right knee (1.9%).

CONCLUSIONS

Geriatric hospitalized Black patients demonstrated a higher prevalence of chronic itch compared with the White cohort, which may be related to the higher prevalence of chronic kidney disease in different stages of severity in this population.

Novel proresolving lipid mediator mimetic 3-oxa-PD1n-3 docosapentaenoic acid reduces acute and chronic itch by modulating excitatory and inhibitory synaptic transmission and astroglial secretion of lipocalin-2 in mice

ABSTRACT

Specialized proresolving mediators (SPMs) have demonstrated potent analgesic actions in animal models of pathological pain. The actions of SPMs in acute and chronic itch are currently unknown. Recently, n-3 docosapentaenoic acid (DPA) was found to be a substrate for the biosynthesis of several novel families of SPMs and 3-oxa-PD1 n-3 DPA (3-oxa-PD1) is an oxidation-resistant metabolic stable analogue of the n-3 DPA-derived protectin D1 (PD1). In this article, we demonstrate that 3-oxa-PD1 effectively reduces both acute and chronic itch in mouse models. Intrathecal injection of 3-oxa-PD1 (100 ng) reduced acute itch induced by histamine, chloroquine, or morphine. Furthermore, intrathecal 3-oxa-PD1 effectively reduced chronic itch, induced by cutaneous T-cell lymphoma (CTCL), allergic contact dermatitis with dinitrofluorobenzene, and psoriasis by imiquimod. Intratumoral injection of 3-oxa-PD1 also suppressed CTCL-induced chronic itch. Strikingly, the antipruritic effect lasted for several weeks after 1-week intrathecal 3-oxa-PD1 treatment. Whole-cell recordings revealed significant increase in excitatory postsynaptic currents in spinal dorsal horn (SDH) neurons of CTCL mice, but this increase was blocked by 3-oxa-PD1. 3-oxa-PD1 further increased inhibitory postsynaptic currents in SDH neurons of CTCL mice. Cutaneous T-cell lymphoma increased the spinal levels of lipocalin-2 (LCN2), an itch mediator produced by astrocytes. 3-oxa-PD1 suppressed LCN2 production in CTCL mice and LCN2 secretion in astrocytes. Finally, CTCL-induced anxiety was alleviated by intrathecal 3-oxa-PD1. Our findings suggest that 3-oxa-PD1 potently inhibits acute and chronic itch through the regulation of excitatory or inhibitory synaptic transmission and astroglial LCN2 production. Therefore, stable SPM analogs such as 3-oxa-PD1 could be useful to treat pruritus associated with different skin injuries.

Central medial thalamic nucleus dynamically participates in acute itch sensation and chronic itch-induced anxiety-like behavior in male mice

Itch is an annoying sensation consisting of both sensory and emotional components. It is known to involve the parabrachial nucleus (PBN), but the following transmission nodes remain elusive. The present study identified that the PBN-central medial thalamic nucleus (CM)-medial prefrontal cortex (mPFC) pathway is essential for itch signal transmission at the supraspinal level in male mice. Chemogenetic inhibition of the CM-mPFC pathway attenuates scratching behavior or chronic itch-related affective responses. CM input to mPFC pyramidal neurons is enhanced in acute and chronic itch models. Specifically chronic itch stimuli also alter mPFC interneuron involvement, resulting in enhanced feedforward inhibition and a distorted excitatory/inhibitory balance in mPFC pyramidal neurons. The present work underscores CM as a transmit node of the itch signal in the thalamus, which is dynamically engaged in both the sensory and affective dimensions of itch with different stimulus salience.

Endogenous Opioid Imbalance as a Potential Factor Involved in the Pathogenesis of Chronic Kidney Disease-Associated Pruritus in Dialysis Patients

Chronic pruritus is one of the most common symptoms of dermatological diseases. It may occur in the course of other disorders, such as kidney disease. Chronic kidney disease-associated pruritus (CKD-aP) most often affects people with end-stage renal disease. The etiology of this condition is still not fully understood, but researchers are currently focusing on a thorough analysis of the association between disturbed opioid balance and increased neuronal signaling leading to pruritus. The aim of this study is to assess the concentration of endogenous opioids in dialysis patients with and without pruritus and in the control group, and to determine the correlation between the concentration of these substances and the occurrence and severity of itching. The study involved 126 dialysis patients and 50 healthy controls. Patients were divided into groups with pruritus (n = 62) and without pruritus (n = 64). The severity of pruritus was assessed using the NRS scale. The concentration of endogenous opioids was determined using the ELISA. The concentration of met-enkephalin was higher in the group of patients with pruritus compared to the control group. Moreover, significantly lower levels of β-endorphin and dynorphin A were observed in the group of dialysis patients compared to the control group. In addition, a statistically significant difference was seen between the β-endorphin concentration in the group of dialysis patients with pruritus compared to the group without pruritus. The ratio of β-endorphin/dynorphin A concentrations was significantly lower in the group of patients with pruritus compared to patients without pruritus and the control group. No correlations were found between serum level of studied opioids and the severity of pruritus. The concentrations of the studied opioids did not correlate with the severity of pruritus. Observed opioid imbalance may affect the occurrence of CKD-aP in dialysis patients, but a thorough understanding of the mechanism of action of these substances in the sensation of pruritus is necessary to assess the possibility of finding a new therapeutic target.

Novel insight on GRP/GRPR axis in diseases

The gastrin-releasing peptide receptor (GRPR), a member of the G protein-coupled receptors (GPCRs), binds to ligands such as gastrin-releasing peptide (GRP) and plays a variety of biological roles. GRP/GRPR signalling is involved in the pathophysiological processes of many diseases, including inflammatory diseases, cardiovascular diseases, neurological diseases, and various cancers. In the immune system, the unique function of GRP/GRPR in neutrophil chemotaxis suggests that GRPR can be directly stimulated through GRP-mediated neutrophils to activate selective signalling pathways, such as PI3K, PKC, and MAPK, and participate in the occurrence and development of inflammation-related diseases. In the cardiovascular system, GRP increases intercellular adhesion molecule 1 (ICAM-1) and induces vascular cell adhesion molecule-1 (VCAM-1). GRP activates ERK1/2, MAPK, and AKT, leading to cardiovascular diseases, including myocardial infarction. Central nervous system signal transduction mediated by the GRP/GRPR axis plays a vital role in emotional responses, social interaction, and memory. The GRP/GRPR axis is elevated in various cancers, including lung, cervical, colorectal, renal cell, and head and neck squamous cell carcinomas. GRP is a mitogen in a variety of tumour cell lines. Its precursor, pro-gastrin-releasing peptide (ProGRP), may play an important role as an emerging tumour marker in early tumour diagnosis. GPCRs serve as therapeutic targets for drug development, but their function in each disease remains unclear, and their involvement in disease progression has not been well explored or summarised. This review lays out the above mentioned pathophysiological processes based on previous research conclusions. The GRP/GRPR axis may be a potential target for treating multiple diseases, and the study of this signalling axis is particularly important.

How to get rid of itching

Itch is an unpleasant sensation arising from a variety of dermatologic, neuropathic, systemic, and psychogenic etiologies. Various itch pathways are implicated according to the underlying etiology. A variety of pruritogens, or itch mediators, as well as receptors have been identified and provide potential therapeutic targets. Recent research has primarily focused on targeting inflammatory cytokines and Janus kinase signaling, protease-activated receptors, substance P and neurokinin, transient receptor potential-vanilloid ion channels, Mas-related G-protein-coupled receptors (MRGPRX2 and MRGPRX4), the endogenous opioid and cannabinoid balance, and phosphodiesterase 4. Periostin, a newly identified pruritogen, should be further explored with clinical trials. Drugs targeting neural sensitization including the gabergic system and P2X3 are other potential drugs for chronic itch. There is a need for more targeted therapies to improve clinical outcomes and reduce side effects.

Differences between aquagenic and non-aquagenic pruritus in myeloproliferative neoplasms: An observational study of 500 patients

BACKGROUND

Pruritus is a frequent symptom experienced by patients with myeloproliferative neoplasms (MPN). Aquagenic pruritus (AP) is the most common type. The Myeloproliferative Neoplasm-Symptom Assessment Form Total Symptom Score (MPN-SAF TSS) self-report questionnaires were distributed to MPN patients before consultations.

OBJECTIVES

The aim of this study was to assess clinical incidence (phenotypical evolution and response to treatment) of pruritus, especially AP, in MPN patients during their follow-ups.

PATIENTS AND METHODS

We collected 1444 questionnaires from 504 patients [54.4% essential thrombocythaemia (ET) patients, 37.7% polycythaemia vera (PV) patients, and 7.9% primary myelofibrosis (PMF) patients].

RESULTS

Pruritus was reported by 49.8% of the patients, including 44.6% of AP patients, regardless of type of MPN or driver mutations. Patients suffering from pruritus were more symptomatic and had a higher rate of evolution into myelofibrosis/acute myeloid leukaemia (19.5% vs. 9.1%, OR = 2.42 [1.39; 4.32], p = 0.0009) than MPN patients without pruritus. Patients with AP had the highest pruritus intensity values (p = 0.008) and a higher rate of evolution (25.9% vs. 14.4%, p = 0.025, OR = 2.07) than patients with non-AP. Disappearance of pruritus was observed in only 16.7% of AP cases, compared to 31.7% of cases with other types of pruritus (p < 0.0001). Ruxolitinib and hydroxyurea were the most effective drugs to reduce AP intensity.

CONCLUSIONS

In this study, we demonstrate the global incidence of pruritus across all MPN. Pruritus, especially AP, which is a major constitutional symptom observed in MPN, should be assessed in all MPN patients due to higher symptom burden and higher risk of evolution.

Mechanisms and treatments of neuropathic itch in a mouse model of lymphoma

Our understanding of neuropathic itch is limited due to a lack of relevant animal models. Patients with cutaneous T cell lymphoma (CTCL) experience severe itching. Here, we characterize a mouse model of chronic itch with remarkable lymphoma growth, immune cell accumulation, and persistent pruritus. Intradermal CTCL inoculation produced time-dependent changes in nerve innervations in lymphoma-bearing skin. In the early phase (20 days), CTCL caused hyperinnervations in the epidermis. However, chronic itch was associated with loss of epidermal nerve fibers in the late phases (40 and 60 days). CTCL was also characterized by marked nerve innervations in mouse lymphoma. Blockade of C-fibers reduced pruritus at early and late phases, whereas blockade of A-fibers only suppressed late-phase itch. Intrathecal (i.t.) gabapentin injection reduced late-phase, but not early-phase, pruritus. IL-31 was upregulated in mouse lymphoma, whereas its receptor Il31ra was persistently upregulated in Trpv1-expressing sensory neurons in mice with CTCL. Intratumoral anti-IL-31 treatment effectively suppressed CTCL-induced scratching and alloknesis (mechanical itch). Finally, i.t. administration of a TLR4 antagonist attenuated pruritus in early and late phases and in both sexes. Collectively, we have established a mouse model of neuropathic and cancer itch with relevance to human disease. Our findings also suggest distinct mechanisms underlying acute, chronic, and neuropathic itch.

Pruritus in Chronic Liver Disease

Pruritus can be associated with chronic liver disease, particularly cholestatic liver disease. Although the pathophysiology is uncertain, there are a few proposed mechanisms and much is still being discovered. Workup involves an assessment to rule out a dermatologic, neurologic, psychogenic, or other underlying systemic disorder. First-line therapy is cholestyramine, which is generally well tolerated and effective. In those who fail cholestyramine, alternative drugs including rifampicin and μ-opioid receptor antagonists can be considered. If medical therapy is ineffective and pruritus is significant, alternative experimental therapies such as albumin dialysis, photopheresis, plasmapheresis, and biliary diversion can be considered.

Uremic pruritus: pathophysiology, clinical presentation, and treatments

Uremic pruritus is one of the most common and bothersome symptoms in patients with end-stage renal disease. Most patients with uremic pruritus experience a prolonged and relapsing course and significant impairments of quality of life. The pathophysiology of uremic pruritus is not completely understood. A complex interplay among cutaneous biology and the nervous and immune systems has been implicated, with the involvement of various inflammatory mediators, neurotransmitters, and opioids. Uremic pruritus treatment outcomes are often unsatisfactory. Clinical trials have mostly been small in scale and have reported inconsistent results. Recent evidence shows that gabapentinoids, nalfurafine, and difelikefalin are effective for relieving uremic pruritus in hemodialysis patients. This review provides an overview of the epidemiology and proposed mechanisms of uremic pruritus, then highlights the manifestations of and clinical approach to uremic pruritus. Current evidence regarding treatment options, including topical treatments, treatment of underlying disease, phototherapy, and systemic treatments, is also outlined. With a better understanding of uremic pruritus, more therapeutic options can be expected in the near future.

Acid-sensing ion channel 3 is required for agmatine-induced histamine-independent itch in mice

Introduction

Itch is a common symptom of many skin and systemic diseases. Identifying novel endogenous itch mediators and the downstream signaling pathways involved will contribute to the development of new strategies for the treatment of chronic itch. In the present study, we adopted behavioral testing, patch clamp recording and metabonomics analysis to investigate the role of agmatine in itch and the underlying mechanism.

Methods

Behavioral analysis was used to evaluate the establishing of acute and chronic itch mice model, and to test the effects of different drugs or agents on mice itch behavior. Western blotting analysis was used to test the effect of agmatine on phosphorylation of ERK (p-ERK) expression in the spinal cord. Patch clamp recording was used to determine the effect agmatine on the excitability of DRG neurons and the role of ASIC3. Finally, the metabonomics analysis was performed to detect the concentration of agmatine in the affected skin under atopic dermatitis or psoriasis conditions.

Results

We fused a mouse model and found that an intradermal injection of agmatine (an endogenous polyamine) into the nape of the neck or cheek induced histamine-independent scratching behavior in a dose-dependent manner. In addition, the ablation of nociceptive C-fibers by resiniferatoxin (RTX) abolished agmatine-induced scratching behavior. However, agmatine-induced itch was not affected by the pharmacological inhibition of either transient receptor potential vanilloid 1 (TRPV1) or transient receptor potential ankyrin 1 (TRPA1); similar results were obtained from TRPV1^-/- or TRPA1^-/- mice. Furthermore, agmatine-induced itch was significantly suppressed by the administration of acid-sensing ion channel 3 (ASIC3) inhibitors, APETx2 or amiloride. Agmatine also induced the upregulation of p-ERK in the spinal cord; this effect was inhibited by amiloride. Current clamp recording showed that the acute perfusion of agmatine reduced the rheobase and increased the number of evoked action potentials in acute dissociated dorsal root ganglion (DRG) neurons while amiloride reversed agmatine-induced neuronal hyperexcitability. Finally, we identified significantly higher levels of agmatine in the affected skin of a mouse model of atopic dermatitis (AD) when compared to controls, and the scratching behavior of AD mice was significantly attenuated by blocking ASIC3.

Discussion

Collectively, these results provide evidence that agmatine is a novel mediator of itch and induces itch via the activation of ASIC3. Targeting neuronal ASIC3 signaling may represent a novel strategy for the treatment of itch.

[Neuropathic pruritus-Evidence-based treatment recommendations]

Neuropathic pruritus is a previously neglected symptom of a wide range of neurological diseases. Peripheral nerve or root compression syndromes, space-occupying lesions of the central nervous system, chronic inflammatory neurological diseases and polyneuropathy can cause neuropathic pruritus. Even when the identification of the underlying neurological disease is successful, a direct causal treatment is not always possible, hence an effective symptomatic treatment remains the only therapeutic option. The purpose of this review article is to present the current literature on various therapeutic agents and options in the treatment of neuropathic pruritus.

Etiopathogenesis of chronic kidney disease-associated pruritus: putting the pieces of the puzzle together

Defined as the unpleasant sensation that causes the desire to scratch, pruritus is the most common skin symptom associated with uremia and appears in almost half of patients with advanced chronic kidney disease (CKD). Beyond its direct impact on quality of life, CKD-associated pruritus (CKD-aP) is an independent predictor of mortality that also has a synergistic effect with other quality of life-related symptoms, such as insomnia, depression, and anxiety. Although different mechanisms have been proposed to explain the origin of Pa-ERC, its etiopathogenesis is still not fully understood. Since new therapeutic targets have been identified and several clinical trials have recently shown promising results, our current understanding of the interrelationships has expanded significantly and the pathophysiological mechanisms underlying CKD-aP are now considered to be multifactorial. The potential triggers of pruritus in patients with CKD are discussed in this review, including hypotheses about skin xerosis, accumulation of uremic toxins, dysregulation of the immune system and systemic inflammation, uremic neuropathy, and imbalances in the endogenous opioid system. Other non-uremic causes of pruritus are also discussed, with the aim of guiding the physicians to apply an adequate aetiopathogenic approach to CKD-aP in their day-to-day clinical practice.

Keratinocyte TLR2 and TLR7 contribute to chronic itch through pruritic cytokines and chemokines in mice

Although neuronal Toll-like receptors (TLRs) (e.g., TLR2, TLR3, and TLR7) have been implicated in itch sensation, the roles of keratinocyte TLRs in chronic itch are elusive. Herein, we evaluated the roles of keratinocyte TLR2 and TLR7 in chronic itch under dry skin and psoriasis conditions, which was induced by either acetone-ether-water treatment or 5% imiquimod cream in mice, respectively. We found that TLR2 and TLR7 signaling were significantly upregulated in dry skin and psoriatic skin in mice. Chronic itch and epidermal hyperplasia induced by dry skin or psoriasis were comparably reduced in TLR2 and TLR7 knockout mice. In the dry skin model, the enhanced messenger RNA (mRNA) expression levels of pruritic CXCL1/2, IL-31, IL-33, ST2, IL-6, IL-17A, TNF-α, and IFN-γ were inhibited in TLR2^-/- mice, while CXCL2, IL-31, and IL-6 were inhibited in TLR7^-/- mice. In psoriasis model, the enhanced mRNA expression levels of pruritic CXCL1/2, IL-31, IL-33, ST2, IL-6, and TNF-α were inhibited in TLR2^-/- mice, while CXCL1/2, IL-31, IL-33, ST2, IL-6, IL-17A, and TNF-α were inhibited in TLR7^-/- mice. Incubation with Staphylococcus aureus (S. aureus) peptidoglycan (PGN-SA) (a TLR2 agonist), imiquimod (a TLR7 agonist), and miR142-3p (a putative TLR7 agonist) were sufficient to upregulate the expression of pruritic cytokines or chemokines in cultured keratinocyte HaCaT cells. Finally, pharmacological blockade of C-X-C Motif Chemokine Receptor 1/2 and high mobility group box protein 1 dose-dependently attenuated acute and chronic itch in mice. Together, these results indicate that keratinocyte TLR2 and TLR7 signaling pathways are distinctly involved in the pathogenesis of chronic itch.

Upregulation of DRG protein TMEM100 facilitates dry-skin-induced pruritus by enhancing TRPA1 channel function

The dry skin tortures numerous patients with severe itch. The transient receptor potential cation channel V member 1 (TRPV1) and A member 1 (TRPA1) are two essential receptors for peripheral neural coding of itch sensory, mediating histaminergic and nonhistaminergic itch separately. In the dorsal root ganglion, transmembrane protein 100 (TMEM100) is structurally related to both TRPV1 and TRPA1 receptors, but the exact role of TMEM100 in itch sensory coding is still unknown. Here, in this study, we find that TMEM100 ⁺ DRG neurons account for the majority of activated neurons in an acetone-ether-water (AEW)-induced dry skin itch model, and some TMEM100 ⁺ DRG neurons are colocalized with both TRPA1 and the chloroquine-related Mrgpr itch receptor family. Both the expression and function of TRPA1 channels, but not TRPV1 channels, are upregulated in the AEW model, and specific DRG Tmem100 gene knockdown alleviates AEW-induced itch and rescues the expression and functional changes of TRPA1. Our results strongly suggest that TMEM100 protein in DRG is the main facilitating factor for dry-skin-related chronic itch, and specific suppression of TMEM100 in DRG could be a novel effective treatment strategy for patients who suffer from dry skin-induced itch.

Role of kappa-opioid and mu-opioid receptors in pruritus: Peripheral and central itch circuits

Modern genetic approaches in animal models have unveiled novel itch-specific neural pathways, emboldening a paradigm in which drugs can be developed to selectively and potently target itch in a variety of chronic pruritic conditions. In recent years, kappa-opioid receptors (KORs) and mu-opioid receptors (MORs) have been implicated in both the suppression and promotion of itch, respectively, by acting on both the peripheral and central nervous systems. The precise mechanisms by which agents that modulate these pathways alleviate itch remains an active area of investigation. Notwithstanding this, a number of agents have demonstrated efficacy in clinical trials that influence both KOR and MOR signalling. Herein, we summarize a number of opioid receptor modulators in development and their promising efficacy across a number of chronic pruritic conditions, such as atopic dermatitis, uremic pruritus and beyond.

Can contagious itch be affected by positive and negative suggestions?

Contagious itch can be evoked by observing people scratching. Verbal suggestions about to-be-received itch can influence itch intensity, as shown by placebo research, but it is unknown whether this extends to contagious itch. The current study aimed to replicate prior findings that listening to scratching and rubbing sounds elicits contagious itch, and to investigate whether suggestions can modulate this process. Healthy participants (n = 140) received positive or negative suggestions about itch in response to the sounds (aimed to decrease or increase expected itch, respectively), or no specific suggestions as a control. Participants listened to a number of audio fragments with scratching and rubbing sounds. The amount of expected itch as well as itch sensation after each audio fragment were measured by self-report. Suggestions had no effect on the expected itch. Both rubbing and scratching sounds significantly elicited itch in all groups. Scratching sounds induced more itch than rubbing sounds exclusively in the control group. These findings indicate that short suggestions might be not effective enough to modify the expectations of people regarding contagious itch. Furthermore, suggestions modulate contagious itch to some degree, but not in the hypothesized direction. Potential similarities and differences in the neurobiological mechanisms of contagious itch and nocebo effects are discussed.

Effectiveness of Sopoongsan for chronic upper body pruritus in patients with atopic or seborrheic dermatitis: A pilot study protocol for a randomized, double-blind, placebo-controlled, parallel trial

INTRODUCTION

Chronic pruritus persists for > 6 weeks and is known to decrease patients' quality of life. Due to the complex pathological mechanism of chronic pruritus, there is still a lack of satisfactory therapeutic agents; therefore, complementary therapies are required to improve itching symptoms. In the Republic of Korea, Sopoongsan, an herbal formula, has been used to treat itching, dizziness, and skin paralysis. To our knowledge, this is the first study to evaluate whether Sopoongsan improves chronic pruritus and to identify Sopoongsan-related changes in the immune response in patients with chronic upper body pruritus.

METHODS

A randomized, double-blind, placebo-controlled parallel trial will be conducted to assess 20 patients with chronic upper body pruritus for 3 months who have been diagnosed with allergic atopic dermatitis or seborrheic dermatitis. The patients will be randomly allocated to either the placebo-control (n = 10) or treatment (n = 10) group. The total study period will be 8 weeks (i.e., administration of Sopoongsan or placebo drugs for 4 wk and follow-up for 4 wk). Participants will be allowed to receive external treatment, except for antipruritic medications administered orally, throughout the study period. The primary outcome measure will be the numeric rating scale results for itching, whereas the secondary outcome measures will be questionnaire survey (Dermatological Life Quality Index and Epworth Sleepiness Scale) findings and the immune response index, including interferon gamma, interleukin-4, immunoglobulin E, thymic stromal lymphopoietic protein, and histamine, to investigate the biological mechanisms underlying chronic pruritus.

DISCUSSION AND CONCLUSIONS

We expect that the results of this study will provide important clinical evidence regarding the effectiveness of Sopoongsan on itching symptoms, quality of life, sleep disturbance, and changes in the immune response. The findings will help elucidate the mechanism underlying the therapeutic effect of Sopoongsan for chronic pruritus and lay the foundation for further studies in this area.

Peristomal Skin Itch: An Integrative Review

Survey data from the United Stated, the United Kingdom, and the Netherlands indicate peristomal itch is prevalant among ostomy patients. Pruritus has a significant negative impact on health-related quality of life, resulting in discomfort and interrupted sleep. In ostomy patients, peristomal skin scratching also may interfere with adherence of the ostomy pouching system. This article reviews the classification and pathophysiology of itch in the peristomal skin, along with options for its management.

Complementary and integrative remedies in the treatment of chronic pruritus: A review of clinical trials

BACKGROUND

Chronic pruritus is one of the most common conditions in dermatology and a common manifestation in many systemic diseases. Since the etiology of chronic pruritus remains somewhat unknown, hence, conventional medications may not always show a good therapeutic response. This finding has led both investigators and patients to use herbal and complementary remedies for its treatment. The aim of this study was to review clinical trials in which herbal and complementary medicine was used in the control and treatment of chronic pruritus.

MATERIALS AND METHODS

In this study, we reviewed related articles in this domain, from 2000 to 2020. The search involved electronic databases including PubMed, Scopus, Web of Science, Cochrane, Google Scholar, and SID databases using the keywords "pruritus," "itch," "herb," "complementary medicine," "traditional medicine," "integrative medicine," and their related MeSH terms. Finally, we extracted the pertinent information from these articles and summarized the results.

RESULTS

The findings of this study showed that 17 clinical trials have been conducted till date in order to evaluate the efficacy of herbal remedies and complementary medicines in the treatment of chronic pruritus. Herbal remedies including turmeric, Fumaria parviflora, Avena sativa, capsaicin, sweet almond oil, peppermint oil, violet oil, vinegar, as well as manual therapies including aromatherapy, auricular acupressure, and acupuncture, were significantly effective in the treatment of chronic pruritus.

CONCLUSION

There are only a few studies published on the therapeutic efficacy of herbal remedies and complementary medicine in the treatment of chronic pruritus. Some have shown promising results. Therefore, more evidence-based studies are needed in order to determine if herbal remedies and complementary medicine could be an effective alternative or adjuvant treatment modality in chronic pruritus.

Footedness for scratching itchy eyes in rodents

The neural bases of itchy eye transmission remain unclear compared with those involved in body itch. Here, we show in rodents that the gastrin-releasing peptide receptor (GRPR) of the trigeminal sensory system is involved in the transmission of itchy eyes. Interestingly, we further demonstrate a difference in scratching behaviour between the left and right hindfeet in rodents; histamine instillation into the conjunctival sac of both eyes revealed right-foot biased laterality in the scratching movements. Unilateral histamine instillation specifically induced neural activation in the ipsilateral sensory pathway, with no significant difference between the activations following left- and right-eye instillations. Thus, the behavioural laterality is presumably due to right-foot preference in rodents. Genetically modified rats with specific depletion of Grpr-expressing neurons in the trigeminal sensory nucleus caudalis of the medulla oblongata exhibited fewer and shorter histamine-induced scratching movements than controls and eliminated the footedness. These results taken together indicate that the Grpr-expressing neurons are required for the transmission of itch sensation from the eyes, but that foot preference is generated centrally. These findings could open up a new field of research on the mechanisms of the laterality in vertebrates and also offer new potential therapeutic approaches to refractory pruritic eye disorders.

Lichen Simplex Chronicus Itch: An Update

Lichen simplex chronicus is a form of chronic localized pruritus with a secondary dermatitis, and one of the most common types of chronic itch conditions, estimated to affect more than 10% of the general population. However, despite its prevalence and burden, there has been limited research into the pathogenesis and aetiology of lichen simplex chronicus, which, historically, made it a challenging condition to treat. In recent years, our understanding of this condition, along with that of pruritus and the itch-scratch cycle, has increased greatly, enabling a substantial increase in treatment options. In addition, there are several new promising treatments currently in development and trials. This article discusses the definition, epidemiology, clinical characteristics, pathophysiology, and current therapeutic options for lichen simplex chronicus, in order to highlight recent advancements in this field.

Inhibitory effects of antibiotic-induced gut microbiota depletion on acute itch behavior in mice

BACKGROUND

The gut microbiota is known to be associated with the regulation of many neurological diseases and behaviors, including chronic pain. However, it is unclear whether the gut microbiota is critical to the itch sensation. In this study, we investigated the effects of gut microbiota depletion on acute itch.

METHODS

First, an antibiotic cocktail was orally administered to deplete the gut microbiota in male C57BL/6 mice. Then, pruritogens were intradermally injected to induce acute itch behavior. In addition, antibiotic-treated mice received transplantation of fecal microbiota from untreated mice, followed by tests for acute itch. The changes in c-Fos expression in trigeminal ganglia (TG) neurons were also investigated by immunofluorescence staining.

RESULTS

Our results indicated that chronic antibiotic treatment significantly reduced the diversity and richness of the gut microbiota of mice. Compared to vehicle-treated mice, antibiotic-treated mice showed reductions in acute itch behavior induced by compound 48/80, chloroquine (CQ), and serotonin (5-HT), respectively. Moreover, repositioning of microbiota reversed the reductions in acute itch behavior in antibiotic-treated mice. In addition, immunofluorescence staining revealed that antibiotic-treated mice displayed decreased c-Fos expression in ipsilateral TG compared to controls.

CONCLUSIONS

Our study, for the first time, discovered that antibiotic-induced gut microbiota depletion could reduce acute itch behavior, which may be connected with decreased TG neuronal activity.

Disease burden of primary biliary cholangitis and associated pruritus based on a cross-sectional US claims analysis

Objective

In order to identify areas of unmet need in patients with primary biliary cholangitis (PBC), this study sought to use real-world observational healthcare data to characterise the burden in patients with PBC and in PBC patients with a recorded diagnosis of pruritus.

Design

This retrospective, cross-sectional database study compared prevalence of prespecified comorbidities and medications in the PBC population and PBC-pruritus subpopulation with non-cases using an indirect standardisation approach. The PBC population was identified from the US IBM MarketScan Commercial Claims and Medicare Supplemental Database during 2016 using International Classification of Diseases 10th Revision, Clinical Modification codes (≥2 claims for PBC); the PBC-pruritus subpopulation additionally had ≥1 claim for pruritus during this period. Non-cases had no claims for PBC. Indirect age-sex standardised prevalence ratios (iSPR) and 95% confidence intervals (CIs) were calculated for prespecified comorbidities and medications recorded during 2017.

Results

The PBC population (N=1963) and PBC-pruritus subpopulation (N=139) had significantly higher prevalence of fatigue (19.9%, iSPR (95% CI): 1.51 (1.36 to 1.66); 26.6%, 2.10 (1.48 to 2.90)), depression/anxiety (21.3%, 1.09 (0.99 to 1.20); 28.1%, 1.46 (1.04 to 2.00)) and sleep-related issues (6.9%, 1.18 (0.99 to 1.40); 14.4%, 2.58 (1.58 to 3.99)) compared with non-cases. Bile acid sequestrants were prescribed in 5.8% and 18.0% of the PBC and PBC-pruritus populations, respectively. In general, a higher prevalence of comorbidities and medication use was observed in the PBC-pruritus subpopulation compared with the PBC population and non-cases.

Conclusion

Despite availability of treatments for PBC, the PBC population had a higher burden of comorbidities than non-cases. This burden was even greater among the PBC-pruritus subpopulation, with a particularly high prevalence of sleep disorders and depression/anxiety. Despite this, pruritus remains undertreated highlighting a need for treatments specifically indicated for cholestatic pruritus.

Abrocitinib monotherapy in Investigator's Global Assessment nonresponders: improvement in signs and symptoms of atopic dermatitis and quality of life

BACKGROUND

Abrocitinib, a once-daily, oral Janus kinase 1 selective inhibitor, was shown to be an effective treatment for moderate-to-severe atopic dermatitis in phase 2 b/3 monotherapy trials.

METHODS

These analyses included data for Investigator's Global Assessment responder (clear [0] or almost clear [1] with ≥2-grade improvement) and nonresponder patients with moderate-to-severe atopic dermatitis who received abrocitinib (200 mg or 100 mg) or placebo in three abrocitinib monotherapy trials (phase 2 b, NCT02780167; two phase 3, NCT03349060/JADE MONO-1 and NCT03575871/JADE MONO-2). Outcomes measuring skin clearance, itch, and quality of life were evaluated.

RESULTS

Both nonresponders (n = 548) and responders (n = 260) treated with abrocitinib had rapid and clinically meaningful improvement in skin clearance, itch, and quality of life compared with placebo.

CONCLUSION

Patients with moderate-to-severe atopic dermatitis treated with abrocitinib who did not achieve an Investigator's Global Assessment 0/1 response at week 12 still experienced rapid, clinically meaningful improvements across several other validated measures of efficacy and quality of life.

CLINICALTRIALS.GOV

NCT02780167, NCT03349060, NCT03575871.

Neuroinflammation Involved in Diabetes-Related Pain and Itch

Diabetes mellitus (DM) is a global epidemic with increasing incidence, which results in diverse complications, seriously affects the patient quality of life, and brings huge economic burdens to society. Diabetic neuropathy is the most common chronic complication of DM, resulting in neuropathic pain and chronic itch. The precise mechanisms of diabetic neuropathy have not been fully clarified, hindering the exploration of novel therapies for diabetic neuropathy and its terrible symptoms such as diabetic pain and itch. Accumulating evidence suggests that neuroinflammation plays a critical role in the pathophysiologic process of neuropathic pain and chronic itch. Indeed, researchers have currently made significant progress in knowing the role of glial cells and the pro-inflammatory mediators produced from glial cells in the modulation of chronic pain and itch signal processing. Here, we provide an overview of the current understanding of neuroinflammation in contributing to the sensitization of the peripheral nervous system (PNS) and central nervous system (CNS). In addition, we also summarize the inflammation mechanisms that contribute to the pathogenesis of diabetic itch, including activation of glial cells, oxidative stress, and pro-inflammatory factors. Targeting excessive neuroinflammation may provide potential and effective therapies for the treatment of chronic neuropathic pain and itch in DM.

The Effects of Cannabinoid Agonist, Heat Shock Protein 90 and Nitric Oxide Synthase Inhibitors on Increasing IL-13 and IL-31 Levels in Chronic Pruritus

BACKGROUND

Heat shock protein 90 (Hsp90) inhibitor and cannabinoid agonists ameliorate dry skin-induced chronic itch. We have recently reported that cannabinoids, hsp90 and nitric oxide (NO) are involved in dry skin-induced itch. Here, we investigated the contribution of the Th2 cell signaling pathway to the antipruritic effect of the hsp90 inhibitor 17-Alilamino-17-demethoxygeldanamycin (17-AAG), nitric oxide synthase (NOS) inhibitor Nω-Nitro-L-arginine methyl ester hydrochloride (L-NAME) and cannabinoid agonist WIN 55,212-2 on a dry skin-induced scratch.

METHODS

Dry skin-induced chronic itching was created by topical application of AEW (acetone/diethyl ether/water). WIN 55,212-2 (1 mg/kg, i.p.), L-NAME (1 mg/kg, i.p.) and increasing doses of 17-AAG (1, 3 and 5 mg/kg,i.p.) were administered to Balb/c mice (for each group, n = 6). After these applications, skin tissues were taken from the nape region of all of the mice. Gene and protein expressions of IL-13 and IL-31 were evaluated in skin tissues by RT-PCR and immunohistochemistry, respectively.

RESULTS

IL-13 and IL-31 mRNA expressions and immune positive cell counts were increased in the AEW applied groups. WIN 55,212-2 reduced both of the increased cytokines levels, while L-NAME decreased only the IL-13. 17-AAG dose-dependently reduced the increased cytokine levels. IL-13 and IL-31 levels significantly decreased following the co-administration of these agents.

CONCLUSION

These results show that increased levels of IL-13 and IL-31 are associated with pruritus. Hsp90 inhibition and cannabinoid system activation may induce antipruritic effects through down-regulation of these cytokines.

Safety and Efficacy of Nemolizumab for Atopic Dermatitis With Pruritus: A Systematic Review and Meta-Regression Analysis of Randomized Controlled Trials

Background

Nemolizumab is deemed as a promising drug for atopic dermatitis (AD) patients with pruritus.

Objective

This study aimed to evaluate the efficacy of nemolizumab in treating patients with AD and the association between the dosage or regimen of nemolizumab with the improvement in clinical indices.

Methods and Materials

PubMed, Embase, and the Cochrane Library were searched for randomized controlled trials (RCTs) published from inception to August 2021.

Results

A total of 14 cohorts of participants from six randomized controlled studies were included in the meta-analysis. Nemolizumab significantly reduced the pruritus VAS (WMD = -18.86, 95% CI: -27.57 to -10.15, p < 0.001; I ² = 56.2%, p _{heterogeneity} = 0.005) and EASI (WMD = -11.76, 95% CI: -20.55 to -2.96, p = 0.009; I ² = 0%, p _{heterogeneity} = 0.978) scores compared with placebo. No significant difference was observed in the occurrence of any AEs (RR = 1.03, 95% CI: 0.93 to 1.13, p = 0.593; I ² = 0%, p _{heterogeneity} = 0.980) between the two groups. The univariate meta-regression showed that both the dosage and study duration had no association with the change of pruritus VAS score.

Conclusion

Nemolizumab presented a promising effect based on the difference in the average change in pruritus VAS and EASI scores compared with placebo. The results indicated its efficacy in relieving pruritus and the severity of AD and improving patients' quality of life.

Acupuncture for the Treatment of Itch: Peripheral and Central Mechanisms

Despite the widespread clinical use of acupuncture in the treatment of pruritus caused by psoriasis, urticaria, uremic, and other diseases, insights into the mechanism of action of acupuncture are still emerging. For the above reasons, a beneficial effect of acupuncture on pruritus was not recommended or reported in recent clinical practice guidelines. Acupuncture is a kind of physical stimulation, which has the characteristics of multi-channel and multi-target effects. The biomechanical stimulation signal of acupuncture needling can be transformed into bioelectric and chemical signals; interfere with kinds of cells and nerve fibers in the skin and muscle; alter signaling pathways and transcriptional activity of cells, mediators, and receptors; and result in inhibition of peripheral and central transmission of pruritus. Available mechanistic data give insights into the biological regulation potency of acupuncture for pruritus and provide a basis for more in-depth and comprehensive mechanism research.

Cholestatic pruritus: a knowledge update

This review is focused on updating knowledge about cholestatic pruritus. It summarizes clinical-epidemiological characteristics, pathophysiology, diagnostic approach, and evidence-based therapeutic recommendations regarding this form of pruritus. Pruritus is a frequent symptom that accompanies several liver diseases, particularly cholestatic ones. The symptom may be mild and tolerable, but it can also dramatically reduce the quality of life. Although the exact pathophysiology of this form of pruritus remains unclear, current evidence supports a mixed origin. It is extremely important for dermatologists to have knowledge about cholestatic pruritus since they are usually the first physicians to be sought by the patient when they experience the symptom. In the absence of specific dermatological alterations, cholestasis must always be considered as a possible cause of pruritus. In addition to allowing an adequate diagnosis, a better pathophysiological understanding of hepatic pruritus provides the identification of new therapeutic targets and, consequently, optimization of the approach in patients with this condition.

Study of the Involvement of the P2Y12 Receptor in Chronic Itching in Type 2 Diabetes Mellitus

Itching is a common clinical symptom in diabetic patients. This research is to carry out experiments on the pathological changes in the P2Y12 receptor in type 2 diabetes mellitus complicated with chronic itching. Changes in body weight, fasting blood glucose (FBG), thermal hyperalgesia, cold hyperalgesia, spontaneous itching, and sciatic nerve conduction velocity were detected. The content of reactive oxygen species (ROS) in the dorsal root ganglion was detected by chemical fluorescence. The expression of the P2Y12 receptor, NLRP3, ASC, interleukin-1β (IL-1β), and IL-18 was detected by Western blotting, real-time quantitative PCR, immunofluorescence double labelling, and enzyme-linked immunosorbent assay. Itching and pain behaviours of the mice in the type 2 diabetes mellitus + itch group were significantly increased, and the expression of P2Y12 and NLRP3 as well as the content of ROS increased, and these changes were significantly reversed by treatment with P2Y12 short hairpin RNA (shRNA) or P2Y12 antagonist ticagrelor. Upregulated P2Y12 receptor expression after the activation of satellite glial cells contributes to the increase in ROS content in vivo, followed by NLRP3 inflammasome activation, increased inflammatory cytokine release, and damage to peripheral nerves, which leads to chronic itching. Treatment with P2Y12 shRNA or ticagrelor can inhibit these pathological changes, thus improving itching behaviour. Development mechanism of diabetes mellitus complicated with chronic itching. Notes: The upregulation of P2Y12 receptor expression and the activation of SGCs lead to the increase of ROS content in vivo, followed by the activation of NLRP3 inflammasome, the increase of inflammatory cytokine release, the abnormal excitation of DRG neurons, and the damage of peripheral nerves, resulting in chronic itching. P2Y12 receptor-related inflammatory injury involves chronic itching in type 2 diabetes mellitus. Treatment with P2Y12 receptor shRNA or P2Y12 antagonist ticagrelor can inhibit these pathological changes and improve itching behaviour.

“Look Beyond the Skin”: A case report about chronic pruritus

A healthy 23-year-old female developed generalized pruritus over a year that began on her feet and gradually progressed to involve more than 50% of her entire body surface area. Punch skin biopsies were inconclusive, whereas a two-view chest x-ray was suspicious for lymphadenopathy. A chest computed tomography scan with contrast identified an anterior mediastinal mass which was biopsied and diagnosed as a nodular sclerosis type of Hodgkin’s lymphoma. Subsequently, appropriate therapy was initiated resulting in complete resolution of the patient’s chronic itch. This case underscores the clinical significance of a comprehensive systemic evaluation in chronic pruritus of unclear etiology.

Clinical management of chronic kidney disease-associated pruritus: current treatment options and future approaches

Chronic kidney disease (CKD)-associated pruritus (CKD-aP) is an underdiagnosed yet severely distressing condition that impacts 60% of patients on dialysis and many nondialysis patients with Stages 3–5 CKD. However, despite its high prevalence, there are currently limited treatment options available for these patients and a lack of treatment guidelines for clinicians. In this manuscript, we reviewed the available literature in order to evaluate the current management and treatment options for CKD-aP, including dialysis management, topical treatments, gabapentinoids, opioids and alternative medicine. We also review the available data on CKD-aP treatments in development and propose new guidelines for managing patients with CKD-aP.

Oncostatin M can sensitize sensory neurons in inflammatory pruritus

[Figure: see text].