Epidemiology of Chronic Pruritus: Where Have We Been and Where Are We Going?

Kappa opioid agonists in the treatment of itch: just scratching the surface?

Chronic pruritus is a debilitating condition affecting 23-44 million Americans. Recently, kappa opioid agonists (KOAs) have emerged as a novel class of potent antipruritic agents. In 2021, the Food and Drug Administration approved difelikefalin (Korsuva) for the treatment of moderate-to-severe pruritus associated with chronic kidney disease in adults undergoing hemodialysis. Difelikefalin is a potent, peripherally restricted KOA that is intravenously available. Although promising, difelikefalin is currently available as an intravenous composition only, limiting the scope of use. Oral formulations of difelikefalin did not meet the primary endpoint criteria in recent phase 2 clinical trials; however, additional clinical studies are ongoing. The future for KOAs in the treatment of pruritus is encouraging. Orally active pathway-biased KOAs, such as triazole 1.1, may serve as viable alternatives with broader applications. Extended-release compositions, such as the TP-2021 ProNeura subdermal implant, may circumvent the pharmacokinetic issues associated with peptide-based KOAs. Lastly, dual-acting kappa opioid receptor agonist/mu opioid receptor antagonists are orally bioavailable and may be useful in the treatment of various forms of chronic itch. In this review, we summarize the results of KOAs in clinical and preclinical trials and discuss future directions of drug development.

Pruritogenic Mediators and New Antipruritic Drugs in Atopic Dermatitis

Atopic dermatitis (AD) is a common highly pruritic chronic inflammatory skin disorder affecting 5-20% of children worldwide, while the prevalence in adults varies from 7 to 10%. Patients with AD experience intense pruritus that could lead to sleep disturbance and impaired quality of life. Here, we analyze the pathophysiology of itchiness in AD. We extensively review the histamine-dependent and histamine-independent pruritogens. Several receptors, substance P, secreted molecules, chemokines, and cytokines are involved as mediators in chronic itch. We also, summarize the new emerging antipruritic drugs in atopic dermatitis.

Phase 2 Trial of Difelikefalin in Notalgia Paresthetica

BACKGROUND

Notalgia paresthetica is a neuropathic disorder characterized by pruritus in a circumscribed region of the upper back. Difelikefalin, a selective kappa opioid receptor agonist, has shown efficacy in other chronic pruritic conditions and is being investigated for the treatment of notalgia paresthetica.

METHODS

In this phase 2, double-blind, placebo-controlled trial, we randomly assigned, in a 1:1 ratio, patients with moderate-to-severe pruritus caused by notalgia paresthetica to receive 2 mg of oral difelikefalin or placebo twice daily for 8 weeks. The primary outcome was the change from baseline at week 8 in the weekly mean score on the daily Worst Itch Numeric Rating Scale (WI-NRS; scores range from 0 [no itch] to 10 [worst itch imaginable]). The secondary clinical outcomes were itch-related quality-of-life and itch-related sleep measures.

RESULTS

A total of 126 patients were enrolled; 62 patients were assigned to receive difelikefalin, and 63 were assigned to receive placebo. One patient who had been assigned to receive difelikefalin withdrew consent before the first dose and is not included in the main analyses. The mean baseline WI-NRS score was 7.6 (indicating severe itch) in each group. The change from baseline in the weekly mean WI-NRS score at week 8 was -4.0 points in the difelikefalin group and -2.4 points in the placebo group (difference in change, -1.6 points; 95% confidence interval, -2.6 to -0.6; P = 0.001). The results for the secondary outcomes generally did not support those of the primary analysis. Headache, dizziness, constipation, and increased urine output occurred more frequently in the difelikefalin group than in the placebo group.

CONCLUSIONS

Among patients with notalgia paresthetica, oral treatment with difelikefalin resulted in modestly greater reductions in itch intensity scores than placebo over a period of 8 weeks but was associated with adverse events. Larger and longer trials are needed to assess the efficacy and safety of difelikefalin treatment in this disorder. (Funded by Cara Therapeutics; KOMFORT ClinicalTrials.gov number, NCT04706975.).

Introduction of a Specific Dermatological Rehabilitation Programme for Patients with Chronic Pruritus: A Pilot Study

Chronic pruritus is a common symptom, associated with several severe medical conditions, great psychological burden, and reduced quality of life. It also poses socio-economic challenges concerning patients' work loss and healthcare costs. In Germany, medical rehabilitation programmes represent an integral part of the medical care of patients with chronic inflammatory skin diseases. However, such programmes play only a rudimentary role in the treatment of other dermatological diseases, such as dermatological oncology, genetic skin diseases, and chronic pruritus. Therefore, a specific antipruritic dermatological rehabilitation programme was developed in cooperation between the Department of Dermatology of the Medical Rehabilitation Center Bad Bentheim and the Center for Chronic Pruritus of the University Hospital of Muenster, Germany. This prospective study compared short-term patient-reported outcomes (n = 121) at the beginning and end of the rehabilitation programme. The majority of subjects had chronic pruritus on primary diseased, inflamed skin. Significant improvements in pruritus intensity (p ≤ 0.001), quality of life (p ≤ 0.001), anxiety symptoms (p ≤ 0.001) and depression (p ≤ 0.001), as well as an overall patient-relevant benefit (Patient Benefit Index 2.6 ± 1.06) and treatment-related patients' satisfaction, were shown. This suggests that implementation of this standardized rehabilitation programme for treatment of patients with chronic pruritus was successful.

Validation of the 5-D Itch Scale in Three Ethnic Groups and Exploring Optimal Cutoff Values Using the Itch Numerical Rating Scale

Background

Chronic pruritus is a common and distressing condition that has serious emotional and psychosocial consequences. Due to its subjective nature, self-report questionnaires are widely implemented as cost-effective measures to gauge the severity of chronic pruritus. The current study is aimed at validating the 5-D itch scale in three ethnic groups—Black, Asian, and Hispanic—with the well-validated Itch Numerical Rating Scale (NRS) and Worst Itch NRS (WI-NRS) and developing its cutoff value using receiver operating characteristics (ROC) and inspection of the area under the curve (AUC) across ethnic groups. At the same time, it is aimed at comparing the concurrent prevalence of itch and depression in these populations, who often form ethnic minorities in many countries. The current study addresses the knowledge gap of cultural adaptation of the 5-D pruritus scale for greater usage.

Methods

Community samples of three ethnic groups were recruited from an online platform of Qualtrics and administered the self-report questionnaires of Itch-NRS, 5-D itch scale, and Patient Health Questionnaire-9 (PHQ-9) to measure their pruritus domains, itch intensity, depression screening, and its severity. Informed consent was obtained from all participants. Subgroup analysis was conducted, including concurrent validity and cutoff values compared between each ethnic group. Concurrent prevalence of itch and depression was evaluated using the cutoff value of Itch-NRS and PHQ-9.

Result

A total of 2323 participants were included in the study. A significant positive correlation (p < 0.001) was found between the Itch-NRS, WI-NRS, and 5-D itch scale. The cutoff value of the 5-D itch scale was established for the three ethnic groups using ROC, with a cutoff value of Itch-NRS as a reference.

Conclusions

The 5-D itch scale has demonstrated sound psychometric properties in three ethnic groups and is closely related to Itch-NRS. The analysis of the cutoff value of the 5-D itch scale suggests that different cutoff values should be considered to reduce the inflation of pruritus severity.

Chronic Intractable Pruritus in Chronic Kidney Disease Patients: Prevalence, Impact, and Management Challenges - A Narrative Review

Chronic kidney disease (CKD) is recognized as a leading public health problem and causes numerous health complications. One of the most common and burdensome dermatological symptoms affecting patients undergoing dialysis is CKD-associated pruritus (CKD-aP). This condition not only has a negative impact on sleep, mood, daily activities, and quality of life but also increases the mortality risk of hemodialyzed patients. Despite that, this condition is greatly underestimated in clinical practice. Due to the complex and still not fully understood etiopathogenesis of CKD-aP, the choice of an effective therapy remains a challenge for clinicians. Most common therapeutic algorithms use topical treatment, phototherapy, and various systemic approaches. This review aimed to summarize most recent theories about the pathogenesis, clinical features, and treatment of CKD-aP.

Interleukin-31 Serum And Pruritus Dimension After Acupuncture Treatment In Hemodialysis Patients: A Randomized Clinical Trial

BACKGROUND: Interleukin (IL)-31 serum levels were significantly higher in hemodialysis patients with pruritus, whereas acupuncture in LI11 was shown to improve symptoms of pruritus. However, there is limited information that IL-31 serum levels that correlate with decreased dimensions of the pruritus after acupuncture in LI11 in a hemodialysis patient. AIM: The aim of the study was to demonstrate the impact of acupuncture in LI11 and IL-31 serum level and its correlation with dimensions of the pruritus in hemodialysis patients. METHODS: A randomized clinical trial has been carried out from August 2019 to December 2019 at H. Adam Malik General Hospital, Medan, Indonesia. Sixty patients underwent hemodialysis who were randomly allocated to two groups, one group got acupuncture in Quchi LI11 (intervention group), and the other group got a placebo (control group). IL-31 serum levels and pruritus were measured before and after 6 weeks of acupuncture in both groups. RESULTS: Acupuncture did not significantly reduce IL-31 (p = 0.931) and decreased dimensions: Degree, duration, disability, and distribution of the pruritus between the intervention group and the control group after 6 weeks of acupuncture in LI11. It can be shown that there is no significant correlation between IL-31 serum levels and dimensions of the pruritus. CONCLUSION: This study demonstrates the effect of acupuncture on reducing dimensions of the pruritus not related to IL-31 serum levels. Identifying the action mechanism of acupuncture to minimize pruritus considerably enhances knowledge of the impacts of acupuncture on reducing pruritus in hemodialysis patients.

IL-23 modulates histamine-evoked itch and responses of pruriceptors in mice

Accumulating evidence has highlighted the essential roles of cytokines in itch processing. Although IL-23 and Th17 cytokines are elevated in inflammatory skin disorders, their role in itch is unknown. Here, we investigated the role of IL-23 and IL-17A in itch response using an in vitro calcium imaging of mouse dorsal root ganglion (DRG) neurons and an in vivo behaviour test. Calcium imaging studies revealed that a few DRG neurons (~5%) responded to either IL-23 or IL-17A. Pretreatment cells with IL-23 significantly reduced calcium responses to histamine and capsaicin but not chloroquine. Behaviour experiments showed neither IL-23 nor IL-17A evoked scratching. IL-23 significantly decreased histamine-evoked scratching without affecting chloroquine-evoked scratching. There was no difference in scratching between IL-17A- and vehicle-treated groups. These results indicate that IL-23 might play a role in regulating histaminergic itch via modulation of TRPV1 activity.

[Neuropathic pruritus]

In the past 10 years specific pathways for pruritus have been characterized on a cellular and molecular level but their exact role in the pathophysiology of neuropathic pruritus remains unclear. This also applies to the question which of the competing theories for pruritus, e.g. specificity, temporal/spatial pattern or intensity, would best apply. While experimental trials on mice have mostly confirmed the theory of specificity, the results on humans indicate a role of spatial and temporal patterns. The skin innervation is greatly reduced by the neuropathy and could provide a "spatial contrast pattern" and the axotomy could induce a de novo expression of gastrin-releasing peptide (GRP) in primarily afferent nociceptors and thus modulate spinal pruritus processing. In addition, the overlap of pruritus and pain in neuropathy patients complicates the direct translation from animal experiments and requires collaboration at the clinical level between pain medicine and dermatology.

Use of dupilumab in a patient with atopic dermatitis, severe asthma, and HIV infection

Dupilumab is a monoclonal antibody against interleukin 4 (IL-4) receptor α that blocks signaling from IL-4 and IL-13, essential mediators of T helper 2 (Th2) pathway. To date, all clinical trials investigating the use of dupilumab excluded patients with human immunodeficiency virus. Herein, we describe the safe and successful use of dupilumab in a patient with atopic dermatitis, severe therapy resistant asthma, and HIV infection.

Evaluation of Chronic Pruritus in Patients over Age 65 Who Admitted to Family Medicine Outpatient Clinic

Aim: This study aims to evaluate the hematologic values, multiple drug use, regions with pruritus, number of regions with pruritus, and systematic diseases of patients over age 65 with chronic pruritus. Methods: A detailed evaluation was made of the hematologic values, itchy regions, multiple drug use, and systematic diseases of 102 patients age 65 and older who presented to our Family Health Center within the past year. Results: When the patients were evaluated according to additional disease, 39 (38.2%) patients had one, and 63 (61.8%) patients had more than one additional disease. According to drug use, 36 (35.5%) patients were using one drug, 27 (26.5%) were using two different drugs, and 39 (38.2%) patients were using three or more different drugs. Number of itchy regions was found to have no significant impact on number of additional diseases. There was no significant difference in number of itchy regions according to number of different drugs used. Conclusion: A detailed hematologic, systematic disease, and multiple drug use assessment of patients ages 65 and older who presenting with chronic itching to Family Health centers could establish a general approach to elderly individuals with chronic pruritus.

Chronic Pruritus Responding to Dupilumab-A Case Series

Background: Chronic pruritus is defined as itch lasting for greater than six weeks. Pruritus is a burdensome manifestation of several internal and external disease states with a significant impact on quality of life. Dupilumab has shown promise in treating a number of conditions including atopic dermatitis (AD) and asthma. Its success in reducing pruritus in AD has generated interest regarding its potential application in other pruritic conditions, such as chronic pruritus of unknown origin, uremic pruritus, and pruigo nodularis. Methods: In this retrospective analysis, we present a series of 20 recalcitrant pruritus patients seen at a tertiary center treated with off-label dupilumab at standard AD dosing. Results: Dupilumab was successful at reducing itch in all treated patients, leading to complete resolution in 12/20 patients and an overall mean NRSi reduction of 7.55. Dupilumab was well tolerated with no significant adverse effects. Conclusions: Our case series suggests dupilumab may be a safe and efficacious therapeutic option in several pruritic conditions and demonstrates the need for further studies to better ascertain its place in the pruritus treatment armamentarium.

Multidimensional pruritus assessment in hemodialysis patients

Background

Pruritus is a distressing, life-limiting symptom in chronic renal failure, affecting 40% of patients. This study aimed to determine uremic pruritus prevalence and investigate the multidimensional impact on hemodialysis patients.

Methods

This descriptive study was performed between March and June 2016. The study included 181 patients undergoing hemodialysis session, who reported pruritus in the prior month. Data were collected using the 5-D Itch Scale, which assesses pruritus based on 5 dimensions, i.e., degree, duration, direction, disability, and distribution, with a total score ranging from 5 (no itching) to 25 (maximum severity).

Results

Pruritus prevalence was 49.3%. Patients had a mean score of 13.97 ± 4.11 (moderate severity). The daily duration was 6–12 h (40.3%), with direction “a little bit better but still present” (38.7%) and distribution on the “back, upper arms, chest, and abdomen.” Patients sleep, social life/leisure time, housework and errand were impacted “occasionally”. The score was higher in patients aged ≥65 years, those on hemodialysis for ≥15 or more years, and those undergoing afternoon hemodialysis. The duration of itching was significantly shorter in employed patients.

Conclusion

Assessment and management of itching symptoms in chronic renal failure are a clinical priority both for patients and for health care professionals. The results of this study highlight the importance of multidimensional assessment and support the need for development of standardized and patient-specific symptom management.

Advances in understanding itching and scratching: a new era of targeted treatments

Chronic itch is a significant health burden with few effective treatments. As such, itch researchers seek to understand the mechanisms behind itch and to find potential targets for treatment. The field of itch research is dynamic, and many advances have been made so far this decade. In particular, major steps forward include the identification of new peripheral and central itch mediators and modulators, the discovery of greater roles for immune cells and glia in itch transmission, and a focus on the brain processing of itching and scratching. Finally, several new therapeutic interventions for itch have shown success in clinical trials.