Prurigo Nodularis: Pathogenesis and the Horizon of Potential Therapeutics

Chronic pruritus that lasts for over 6 weeks can present in various forms, like papules, nodules, and plaque types, with prurigo nodularis (PN) being the most prevalent. The pathogenesis of PN involves the dysregulation of immune cell-neural circuits and is associated with peripheral neuropathies, possibly due to chronic scratching. PN is a persistent and challenging condition, involving complex interactions among the skin, immune system, and nervous system. Lesional skin in PN exhibits the infiltration of diverse immune cells like T cells, eosinophils, macrophages, and mast cells, leading to the release of inflammatory cytokines and itch-inducing substances. Activated sensory nerve fibers aggravate pruritus by releasing neurotransmitters, perpetuating a vicious cycle of itching and scratching. Traditional treatments often fail, but recent advancements in understanding the inflammatory and itch transmission mechanisms of PN have paved the way for innovative therapeutic approaches, which are explored in this review.

Clinical Characteristics and Treatment Outcomes of Prurigo Nodularis: A Retrospective Study

BACKGROUND

Prurigo nodularis (PN) is a complex chronic skin disease characterized by severe pruritic nodules. PN is often associated with mental health disorders and chronic medical comorbidities. Until recently, PN treatment has been challenging and difficult.

OBJECTIVES

This study aims to describe the demographic, clinical characteristics, and comorbidities associated with PN. Also, we aim to describe the effectiveness of systemic therapies, including methotrexate, cyclosporine, and narrow band ultraviolet (NB-UVB) in adult patients with PN.

METHODS

This is a retrospective chart review of adult patients diagnosed with PN at Hamilton Health Science Center and/or McMaster University in Hamilton, Ontario, between 2015 and 2023.

RESULTS

The study included 81 patients (57% female). The mean age was 52.8 years, and the mean age of PN diagnosis was 50 years. Reported symptoms included: itching (100%), dry skin (53%), pain (17%), and burning sensation (5%). Lower and upper extremities were the most common areas involved in 93% and 69%, respectively. Mental health disorders were present in 79% of patients, with depression (58%) and anxiety (52%) being the most common. Atopic dermatitis was the most common skin comorbidity noted. Treatments used included cyclosporine, and NB-UVB, and MTX, which resulted in significant improvement of pruritus in 38%, 35%, and 31% of patients, respectively, at week 16.

CONCLUSIONS

PN is associated with increased risk of mental health disorders and other medical comorbidities. Cyclosporine, methotrexate, and NB-UVB therapy may be effective treatment options, however clinicians must consider the potential short- and long-term adverse effects of these treatments.

Risk of incident sleep disorders in patients with prurigo nodularis: A population-level analysis using The Health Improvement Network

Background

Prurigo nodularis (PN) is a chronic inflammatory skin condition characterized by severely itchy and often painful bumps on the arms, legs, and trunk. It is unknown whether patients with PN have increased risk of developing sleep disorders.

Objective

To evaluate the association of PN with sleep disorders.

Methods

This retrospective, population-level, matched-cohort study was conducted using The Health Improvement Network. The study included 4193 patients with newly diagnosed PN and 4193 age, sex, and race/ethnicity-matched controls. A Cox regression model was used to assess the development of sleep disorders, including insomnia, sleep apnea, and restless legs syndrome, in patients with PN compared with control patients.

Results

Compared with controls, PN was associated with insomnia (adjusted hazard ratio [aHR] = 1.77; 95% CI = 1.48-2.12) and overall sleep disorder (aHR = 1.72; 95% CI = 1.46-2.02), but not with sleep apnea (aHR = 1.51; 95% CI = 0.93-2.44) or restless legs syndrome (aHR = 1.54; 95% CI = 0.92-2.57).

Limitations

As a retrospective cohort study, our analysis is subject to potential confounders not already included.

Conclusions

PN was associated with subsequent development of insomnia. Thus, clinicians should consider insomnia among patients with PN and develop strategies for treatment and prevention.

A population pharmacokinetic-pharmacodynamic model evaluating efficacy of nalbuphine extended-release in patients with prurigo nodularis

AIMS

Population pharmacokinetic (PK) and pharmacokinetic-pharmacodynamic (PK-PD) models were used to describe the exposure-response (E-R) relationship between nalbuphine exposure and two widely used rating scales for itch: the Numerical Rating Scale for the subject's 'average'; itch experience (NRS-AV) and the Worst Itch (WI-NRS), with 24-h recall. Simulations based on the model E-R relationship were used to support dose selection for Phase 3 clinical trials and were evaluated with a target of reducing the 7-day average of the 24-h WI-NRS by at least 30% from baseline in most of the analysis population.

METHODS

Data from two clinical trials (NCT02373215: 9 healthy subjects; NCT02174419: 62 subjects with PN), in patients with prurigo nodularis (PN) with moderate to severe itch who received treatment with either of two doses of nalbuphine extended release (ER) or placebo, were used for the analysis. A two-compartment PK model with serial zero and first-order oral absorption was used to describe drug exposure. A maximum effect ( E max ) model with a placebo effect was used to model the itch response endpoints (NRS-AV, WI-NRS).

RESULTS

The PK-PD model predicted the exposure-related reduction in both NRS-AV and WI-NRS over time with approximately 63% and 27% of E max , respectively. Exposures associated with 80% of E max were achieved in about 78% of the patients at 162 mg, twice daily (BID), compared to 35% at 81 mg BID.

CONCLUSION

Simulated dose response indicated that 108 and 162 mg BID doses result in the highest proportion of patients achieving at least a 30% reduction in NRS-AV and WI-NRS, respectively.

Increased IL-31 expression in serum and tissue protein in prurigo nodularis

Background:

Prurigo nodularis (PN) is a chronic pruritic skin disease which can greatly impact patients’ quality of life. Moreover, the pathogenesis remains unclear, making it a difficult-to-treat condition.

Aims:

To investigate the expression of interleukin-31 (IL-31) in serum and skin biopsy specimens of PN patients and healthy subjects and identify its possible correlation to disease severity and itch intensity.

Methods:

Patients with PN and healthy volunteers were recruited for the study. Expression levels of IL-31 were measured by enzyme-linked immunosorbent assay and immunohistochemistry. Baseline characteristics, disease activity, itch intensity, and related laboratory results were collected.

Results:

Forty-three PN patients and 31 healthy subjects participated in our study. The PN patients had significantly higher mean serum IL-31 levels than the healthy subjects (52.9 ± 18.2 versus 36.3 ± 10.7 pg/ml, p < 0.001). Epidermal and dermal PN lesions also exhibited significantly higher IL-31 expression compared with the healthy skin (p < 0.001 and p = 0.01, respectively). However, there was no significant difference in serum or lesional expression of IL-31 by disease severity or itch intensity.

Conclusion:

Increased IL-31 expression in serum and PN lesions suggests that IL-31 has a potential role in the pathogenesis of PN.

Immunotargets and Therapy for Prurigo Nodularis

Prurigo nodularis is a chronic inflammatory skin disease consisting of severely pruritic nodules that can be very debilitating for patients. The basis of this skin condition is immunological dysregulation and neural amplification, driven by T-lymphocytes, mast cells, eosinophilic granulocytes, macrophages, and cytokines mediating itchy processes. Further complicating this already taxing diagnosis is the lack of approved treatment and consensus on management; although there are off-label treatments utilized as therapy. Immunomodulators are the cornerstone of treatment for PN, and additional novel therapies targeting key players in the immunological cascade are currently undergoing investigation. In this review, we will highlight targets of the immune cascade and explore current immunomodulating treatments as well as immunotherapies on the horizon for the management of prurigo nodularis.

On which evidence can we rely when prescribing off-label methotrexate in dermatological practice? - a systematic review with GRADE approach

If an authorized drug is prescribed for a use that is not described in the Summary of Product Characteristics, this is defined as 'off-label use.' Methotrexate is often used off-label for dermatological indications. Off-label use is permitted if physicians can justify the treatment based on scientific evidence available to them. Our objective here was therefore to summarize the evidence for the effectiveness, efficacy, and safety of the dermatological off-label use of methotrexate in a systematic review. We searched MEDLINE, EMBASE, and CENTRAL for studies for evidence on the effectiveness, efficacy, and safety of the off-label use of methotrexate in dermatological indications up to November 2019. We used the GRADE system to rate the quality of the evidence. The search retrieved 34,583 hits of which 3566 were selected after the title and abstract screening. After the full-text screening, 143 studies were included, which involved 3688 patients in total. We found low-quality evidence for the effectiveness, efficacy, and safety of the off-label use of methotrexate in 31 dermatological diseases. To optimize the quality of evidence to support off-label use, we need high-quality studies in which well-characterized patients are treated with standardized treatments regimens using well-validated outcomes relevant to patients and physicians.

The emerging role of dupilumab in dermatological indications

INTRODUCTION

Dupilumab represents a breakthrough in the management of atopic dermatitis (AD), thanks to its powerful T-helper (Th)2-mediated immunity modulating activity. It can reduce the atopic skin molecular signature and induce a significant decrease in the clinical signs and symptoms of AD patients.

AREAS COVERED

Th2 activation has been confirmed or suspected in skin diseases other than AD, and several reports about the treatment with dupilumab in these conditions have been published. In order to review the new indications of dupilumab in dermatology, we performed a search on PubMed, Embase, Cochrane Skin databases, and clinicaltrials.gov.

EXPERT OPINION

The analysis of available literature suggests that dupilumab may have a large application in dermatology, besides AD. Clinical trials are underway on some widespread disease (i.e. chronic urticaria, bullous pemphigoid, alopecia areata, or allergic contact dermatitis). The data are still partial, but they seem to indicate that dupilumab is efficacious and safe. On the other hand, the dupilumab use in some rare skin diseases remains only hypothetical or linked to few case reports. Dupilumab could have a prominent position in the therapeutic algorithm of chronic skin diseases that significantly affect the quality of life of patients, require long-term treatment, or lacking effective therapies.

Can intermittent, time-restricted circadian fasting modulate cutaneous severity of dermatological disorders? Insights from a multicenter, observational, prospective study

The impact of intermittent circadian fasting (ICF) on skin disorders is far to be plenty deciphered. However, the circadian rhythm seems to exert a modulation on dermatoses severity, drug-response, and drug-related side effects. We aimed to evaluate ICF effect in the daily management of dermatological diseases. In this multicenter, prospective observational study we enrolled patients willing to undergo the 2018 ICF (from May 16 to June 14). Dermatoses severity were evaluated at the beginning of ICF (T0) and at the end of ICF (T1) by two independent board-certified dermatologists. Seventy-two patients suffering from different dermatoses volunteered to take part into the study. They displayed a mean age of 40.38 ± 12.46 years (median 41.0 years), 25 subjects were males (34.7% of the entire sample). The median weight change was 0 kg. The overall ICF effect size was -0.58 ([95% CI -0.83 to -0.33], P < .0001, medium effect size). Since in the present investigation no weight loss occurred, we could speculate that the impact of fasting in terms of improvements in the clinical symptoms could be rather due to the perturbation of the human biological clock. Despite our data remain preliminary, a chronobiological approach should be incorporated in the dermatological armamentarium.

Prurigo nodularis comparative treatment outcome in patients attending a tertiary hospital in northern Tanzania

Prurigo nodularis (PN) is a chronic, benign neurodermatitis of unclear etiology characterized by excoriated, intensely pruritic nodules secondary to an intense itch-scratch cycle. PN treatment is still a challenge, and it is frustrating for both dermatologists and patients. The evidence for the effectiveness of a readily available treatment like cryotherapy is limited. To compare the efficacy of cryotherapy vs 0.05% clobetasol propionate in PN patients attending the RDTC, Northern Tanzania, from October 2018 to July 2019. Based on previous year data, it was expected to enroll nine patients. Assent and consent were obtained. Fourteen patients were enrolled, 11 analyzed; intra-subject control done each one-half of the body received either intervention randomly. The cryotherapy was given in two cycles from 5 to 10 s in one session and clobetasol propionate was applied twice daily for 4 weeks. The patients were followed-up weekly by telephone reminded them to apply clobetasol. Data entry and analysis was done in SPSS version 20. Ethical considerations were observed. Eleven patients were analyzed; four (36%) males and seven (64%) females. Cryotherapy had nodule clearance in the 11 patients of 75% to 100% in 11 (100%) and clobetasol propionate only in three of the patients. Seven patients (63.6%) preferred cryotherapy. Cryotherapy preferred above clobetasol propionate.

A prospective study examining the effect of selected topical and systemic drugs on pruritus grading system score and stat 6 expression in patients of prurigo nodularis

Background:

Prurigo nodularis (PN) is a chronic dermatologic condition presenting as multiple papulonodular lesions occurring with intense pruritus. Though numerous agents (topical, systemic, phototherapy and biological drugs) have been tried, the outcomes are variable.

Objectives:

The aim of this study was to assess the role of topical and systemic therapies in primary PN by comparing the Pruritus Grading System (PGS) score at baseline and 1 month post-therapy.

Materials and Methods:

Of 86 diagnosed cases of PN, 49 cases of primary PN were clinically graded by Pruritus Grading System Score (PGSS), and assessed histopathologically by IHC staining (STAT-1, 3, and 6). Apart from topical agents, oral nortriptyline (mild grade), methotrexate (moderate grade) and thalidomide (severe grade) were administered, whereas doxepin was administered for itching. The PGSS was assessed after 1 month of therapy.

Results:

Among 49 patients of PN, the majority of patients showed a significant decrease in PGSS (P = <0.001) in 1 mont, which correlated with STAT-6 expression. The combination of different topical and oral agents resulted in a statistically significant change in severity, though individual drugs did not achieve statistically significant results.

Conclusion:

A combination of selected oral and topical agents can effectively control the severity of PN within one month, and this was found to correlate with STAT 6 expression.

Pathophysiology, diagnosis, and pharmacological treatment of prurigo nodularis

Introduction: Prurigo nodularis (PN) is a chronic inflammatory skin disease characterized by intensely pruritic, hyperkeratotic nodules distributed on the trunk and extensor surfaces of the extremities. PN has a profoundly negative impact on sleep and quality of life in patients with PN. There are currently no U.S. Food and Drug Administration-approved agents and patients are often recalcitrant to current therapies, highlighting the importance of further research into this severely debilitating condition. Areas covered: A PubMed search was conducted to find available literature on the pathophysiology and clinical management of PN. In this review article, we discuss the current understanding of the pathophysiology, recommended diagnostic approach, and treatment options available for PN. Expert opinion/commentary: PN is an extremely difficult condition to treat, because there is a lack of effective therapies available due to our limited understanding of its pathophysiology. Currently, available treatment options are often multimodal due to the intersection of neuroimmune etiologic factors in the pathogenesis of PN. Fortunately, as our knowledge of PN expands, novel treatments targeting specific molecular biomarkers of PN are emerging, providing hope to this long-suffering patient population.

Practical approaches for diagnosis and management of prurigo nodularis: United States expert panel consensus

BACKGROUND

Prurigo nodularis (PN) is a chronic disease characterized by intensely pruritic, raised, nodular lesions. Because there are currently no United States Food and Drug Administration-approved therapies specifically for PN, management is highly variable, and no consensus exists on treatment regimens.

OBJECTIVE

To provide practical guidance to help United States dermatologists diagnose and effectively treat patients with PN.

METHODS

We participated in a roundtable discussion to develop consensus recommendations on diagnosis and treatment of PN from a United States perspective.

RESULTS

The core findings in PN are the presence of firm, nodular lesions; pruritus lasting at least 6 weeks; and a history or signs, or both, of repeated scratching, picking, or rubbing. The diagnostic workup involves a complete review of systems, considering potential systemic diseases, and assessment of disease severity, including disease burden and pruritus intensity. Treatment should be selected based on a patient's clinical presentation, comorbidities, and response to prior treatments and should address both neural and immunologic components of pruritus.

LIMITATIONS

Data on PN are from anecdotal or small clinical trials, and all treatments are currently used off-label.

CONCLUSION

An effective treatment approach for patients with PN should be based on clinical judgment and tailored to the individual needs of the patient.

Topical methotrexate in dermatology: a review of the literature

Background: Systemic methotrexate (MTX) is a useful treatment for many dermatologic conditions, however, the risk of adverse events prevents its use in patients with minimal or localized disease. Topical application of MTX may be an option to avoid the systemic adverse effects of oral MTX.Objective: To assess what is known about the efficacy and safety of topical methotrexate.Methods: A search on Pubmed was conducted. There were no limits on publication date.Results: A total of 963 articles were discovered. Using our exclusion criteria, 916 articles were excluded; 47 articles were used for full text assessment. Topical MTX has been used primarily in psoriasis but also in mycosis fungoides, lymphomatoid papulosis, and oral precancerous lesions. Optimal delivery system and formulation for adequate penetration is still under investigation.Conclusion: The quality of evidence for the utility of topical methotrexate in psoriasis is good, however, for other dermatologic diseases, the quality is poor. Topical MTX with improved delivery methods may be a viable tool against certain localized dermatologic conditions for patients who do not tolerate oral MTX. Further double-blinded randomized controled studies are needed to substantiate the utility of topical methotrexate.

Prurigo nodularis: Pathogenesis and management

Prurigo nodularis is a chronic skin condition characterized by severely pruritic nodules that cause a profound negative impact on quality of life. The second article in this 2-part continuing medical education series focuses on reviewing the pathogenesis of prurigo nodularis and exploring management algorithms for this condition. In addition, we discuss some emerging and novel therapies for treating prurigo nodularis. The first article in this 2-part series describes the broader epidemiology, patient demographics, physical examination findings, and symptoms to aid in the timely recognition and diagnosis of prurigo nodularis.

Association between Prurigo Nodularis and Etiologies of Peripheral Neuropathy: Suggesting a Role for Neural Dysregulation in Pathogenesis

Background: Prurigo nodularis (PN) is an intensely pruritic skin condition of considerable morbidity. However, the pathogenesis of PN and its association with underlying neuropathy is unclear. Objective: We sought to investigate the association between PN and etiologies of peripheral neuropathy. Methods: A cross-sectional analysis of adult patients (≥18-year-old) with PN, AD, and Psoriasis at the Johns Hopkins Health System over a six-year period (January 2013–January 2019) was performed. The strength of association with etiologies of peripheral neuropathy were compared to a control cohort of individuals without PN, as well as those with AD or psoriasis. Results: A total of 1122 patients with PN were compared to 10,390 AD patients, 15,056 patients with psoriasis, and a control cohort of 4,949,017 individuals without PN, with respect to 25 comorbidities associated with peripheral neuropathies. Limitations: Comparisons between peripheral neuropathies and PN represent associations but are not causal relationships. Conclusion: Prurigo nodularis is strongly associated with peripheral neuropathies, suggesting a role for neural dysregulation in pathogenesis.

Treatment-resistant prurigo nodularis: challenges and solutions

Prurigo nodualris (PN) is a chronic condition with highly pruritic, hyperkeratotic papules or nodules arising in the setting of chronic pruritus. While PN may serve as a phenotypic presentation of several underlying conditions such as atopic dermatitis, chronic kidney disease-related pruritus, and neurological diseases, it represents a distinct clinical entity that may persist despite the removal of the underlying cause, if one is identified. Neuronal proliferation, eosinophils, mast cells, and small-fiber neuropathy play a role in the production of pruritus in PN, although the exact mechanism has not yet been established. Identifying an underlying cause, if present, is essential to prevent recurrence of PN. Due to often present comorbidities, treatment is typically multimodal with utilization of topical and systemic therapies. We performed a PubMed/MEDLINE search for PN and present a review of recent developments in the treatment of PN. Treatment typically relies on the use of topical or intralesional steroids, though more severe or recalcitrant cases often necessitate the use of phototherapy or systemic immunosuppressives. Thalidomide and lenalidomide can both be used in severe cases; however, their toxicity profile makes them less favorable. Opioid receptor antagonists and neurokinin-1 receptor antagonists represent two novel families of therapeutic agents which may effectively treat PN with a lower toxicity profile than thalidomide or lenalidomide.

A systematic review of evidence-based treatments for prurigo nodularis

Prurigo nodularis is a chronic dermatologic condition involving the development of multiple cutaneous nodules in the setting of intractable pruritus. Given emerging treatment options for this difficult-to-treat condition, a current review of therapeutics is needed. A systematic review was performed for clinical studies investigating prurigo nodularis treatment published from 1990 to present including ≥5 subjects. A total of 35 articles were assigned a level of evidence according to the Oxford Center for Evidence-based Medicine. All 5 studies investigating topical agents, including corticosteroids, calcineurin inhibitors, calcipotriol, and capsaicin, conveyed some beneficial effect with level of evidence 2b or higher. Six of 8 reports investigating photo- and photochemotherapy achieved levels of evidence 2b or greater and showed good partial response rates. Thalidomide was studied by 6 reports providing evidence of good symptom response, only 2 of which were rated level 2b or greater. Cyclosporine and methotrexate have demonstrated benefit in 4 combined studies, albeit with level 4 evidence. Pregabalin, amitriptyline, paroxetine, fluvoxamine, and neurokinin-1 receptor antagonists have demonstrated promising evidence in 5 level 2b studies. Higher-powered studies and additional randomized controlled trials are needed for the evaluation of safe and efficacious systemic treatment options for prurigo nodularis.

[Chronic prurigo]

Chronic prurigo is a disease characterized by the presence of chronic pruritus and singular or multiple usually hyperkeratotic symmetrically distributed itchy papules, nodules, and/or plaques. This condition is difficult to treat and leads to a substantial impairment of the quality of life. It may originate from dermatological, systemic, neurological, psychiatric/psychosomatic, multifactorial or unknown conditions causing itch, which lead to prolonged scratching behavior and sensitization mechanisms and ultimately to the development of pruriginous lesions. Thorough diagnostic efforts, including a detailed clinical history and physical examination, as well as targeted complementary examinations should be initiated as soon as possible. The German guideline recommends topical steroids and phototherapy as first-choice options. Pimecrolimus and capsaicin (topical), as well as antihistamines, anticonvulsants, and immunosuppressive drugs (systemic) should be considered as valid alternatives.

Low-Dose Systemic Methotrexate Therapy for Recalcitrant Alopecia Areata

Background

Alopecia areata (AA) is an autoimmune skin disease difficult to manage and treat. The pathogenesis of AA features a T-cell-associated autoimmune process, and systemic immunosuppressive therapy is prescribed widely for AA.

Objective

To evaluate the efficacy and tolerance of systemic low-dose methotrexate (LD-MTX) therapy in treatment of recalcitrant AA multiplex.

Methods

In a retrospective, non-controlled study, we evaluated 29 patients with recalcitrant AA treated with LD-MTX and assessed the therapeutic response according to severity of disease, disease duration, cumulative dose of MTX, and drug safety.

Results

MTX was administered twice weekly, and the mean maximum weekly dose was 14.48 mg. The response was A5 (regrowth=100.0%) in 14 (48.3%) patients and A4 (regrowth of 75%~90%) in 12 (41.4%) patients. Three patients had poor response to LD-MTX treatment (A2: n=2 [6.9%], A1: n=1 [3.4%]). All three of the patients showing a poor response had disease durations exceeding 24 months. Relapse was observed in 31% of patients with more than 75% regrowth. Common side-effects were elevated liver enzyme levels and gastrointestinal discomfort.

Conclusion

LD-MTX appears to be an effective and well-tolerated treatment for recalcitrant AA multiplex.

Dermoscopy of prurigo nodularis

The diagnosis of prurigo nodularis is mainly clinical, based on its distinctive features. However, in some cases it may be difficult to differentiate it from other nodular dermatoses only on the clinical basis, thus requiring histopathological examination to reach a definitive diagnosis. The aim of this study was to describe for the first time the dermoscopic features of prurigo nodularis and the useful contribution of dermoscopy in the differential diagnosis of such dermatoses. Fourteen patients with histopathologically proven prurigo nodularis were included in the study. The results of our study suggest that the detection of a "white starburst pattern" surrounding brown-reddish/brown-yellowish crust(s), erosion(s) and/or hyperkeratosis/scales is a useful clue to support the clinical diagnosis of prurigo nodularis, distinguishing it from the other main differential diagnoses.