Neuropathic pruritus

The neuroscience of itch in relation to transdiagnostic psychological approaches

The experience of itch and its associated chronic conditions (i.e., atopic dermatitis) form a significant burden of disease. Knowledge of how the brain processes itch, that might occur uniquely for chronic itch populations, could be used to guide more effective psychotherapeutic interventions for these groups. To build the evidence base for such approaches, we conducted a series of coordinates-based fMRI analyses, to identify the shared neural mechanisms for itch across the published literature. Upon so doing, we identified a core "itch network" that spans the Basal Ganglia/Thalamus, Claustrum and Insula. Additionally, we found evidence that the Paracentral Lobule and Medial Frontal Gyrus, regions associated with cognitive control and response inhibition, deactivate during itch. Interestingly, a separate analysis for chronic itch populations identified significant recruitment of the Left Paracentral Lobule, potentially suggesting the recruitment of cognitive control mechanisms to resist the urge to scratch. We position these results in light of further integrative studies that could use neuroimaging alongside clinical studies, to explore how transdiagnostic psychological approaches-such as mindfulness and compassion training-might help to improve quality of life for individuals who experience chronic itch.

Managing Symptoms of Systemic Sclerosis for the Allergist-Immunologist

PURPOSE OF REVIEW

Systemic sclerosis (SSc) is a chronic, multisystem, autoimmune disease characterized by fibrosis, vasculopathy and immune system dysregulation. We provide a comprehensive review of features of systemic sclerosis that can potentially present to the allergist.

RECENT FINDINGS

A thorough understanding of the management options is crucial for clinicians involved in the care of patients with SSc to optimize clinical outcomes. Management of systemic sclerosis has drastically changed in the last decade and continues to evolve. This review provides an overview of management strategies for the various symptoms including skin, upper and lower airway, gastrointestinal and vascular manifestations. Institution of treatment early in the disease, including referral to rheumatology or specialized scleroderma centers, can help to both prevent and manage disease complications, and improve patient quality-of-life. While the landscape of systemic sclerosis management has evolved, we continue to recognize that there is still a need for better biomarkers and targeted therapies.

[Neuropathy in pruritus medicine : Recommended diagnostics and therapy]

Chronic itch is a frequent and debilitating condition that greatly affects the quality of life of those affected. In a subset of patients, damage to the peripheral or central nervous system constitutes the cause of the itch. Small-fiber neuropathy, nerve compression syndromes, post-herpetic neuralgia, scars and burns are possible conditions affecting the peripheral nervous system potentially causing itch, whereas space-occupying lesions affecting the spinal cord and stroke are examples of conditions that may induce central itch. Neuropathic itch starts on normal appearing skin, is often accompanied by pain sensations and other dysesthesias, and usually relieved by local cold application. Its distribution depends on the affected site of the somatosensory system. A comprehensive medical history is paramount to reach the diagnosis, while complementary diagnostics with skin biopsies for the investigation of cutaneous neuromorphological alterations or medical imaging to rule out nerve impingement may be advised in selected cases. Topical agents such as capsaicin or local anesthetics as well as systemic drugs such as gabapentinoids, antidepressants and opioid receptor modulators are used in the treatment of neuropathic itch. This review article provides an overview of the clinical features, underlying causes, diagnostic workup and therapeutic approach in neuropathic itch.

The COL6A5-p.Glu2272* mutation induces chronic itch in mice

Pruritus is a common irritating sensation that provokes the desire to scratch. Environmental and genetic factors contribute to the onset of pruritus. Moreover, itch can become a major burden when it becomes chronic. Interestingly, the rare Collagen VI alpha 5 (COL6A5) gene variant p.Glu2272* has been identified in two families and an independent patient with chronic neuropathic itch. These patients showed reduced COL6A5 expression in skin and normal skin morphology. However, little progress has been made until now toward understanding the relationships between this mutation and chronic itch. Therefore, we developed the first mouse model that recapitulates COL6A5-p.Glu2272* mutation using the CRISPR-Cas technology and characterized this new mouse model. The mutant mRNA, measured by RT-ddPCR, was expressed at normal levels in dorsal root ganglia and was decreased in skin. The functional exploration showed effects of the mutation with some sex dysmorphology. Mutant mice had increased skin permeability. Elevated spontaneous scratching and grooming was detected in male and female mutants, with increased anxiety-like behavior in female mutants. These results suggest that the COL6A5-p.Glu2272* mutation found in patients contributes to chronic itch and induces in mice additional behavioral changes. The COL6A5-p.Glu2272* mouse model could elucidate the pathophysiological mechanisms underlying COL6A5 role in itch and help identify potential new therapeutic targets.

Impact of neurofibromatosis type 1 on quality of life using the Skindex-29 questionnaire quality of life in NF1

BACKGROUND

Neurofibromatosis type 1 (NF1) is one of the most common RASopathies predisposing affected patients to melanic lesions and benign tumors. NF1 is associated with considerable esthetic and functional burden negatively affecting the patient's quality of life (QoL). This study aims to assess the clinical features of NF1 patients and evaluate their impact on QoL. We identified NF1 patients from a public health database of a region in Spain. All patients underwent clinical and ophthalmological evaluation for NF1 features. We measured QoL using the Spanish version of the Skindex-29.

RESULTS

Forty patients fulfilled the NF1 National Institute of Health criteria when we recruited patients. The median age was 42.00 years (IQR 26.5 -53.75). The median total Skindex-29 score was 12.3 (IQR 5.9-22.4); (emotion: 15.0, IQR 5.0-37.5; symptoms 8.9, IQR 0.0-17.9 and functioning 8.3; IQR 0.5-18.3). Women and NF1 patients with lower educational levels were associated with poorer QoL scores. We identified itching and sleep troubles to influence NF1 patients' QoL negatively.

CONCLUSION

NF1 considerably influences the psychological well-being of NF1 patients. We observed that female and low-educated patients scored higher on the emotional dimension of the Skindex-29 and could, therefore, be more at risk of depression. We also pointed out some "minor symptoms" that negatively impact NF1 patients' QoL such, as itching and sleep troubles which doctors could treat if sought by doctors.

Aetiology, pathogenesis and management of neuropathic itch: A narrative review with recent updates

Neuropathic itch is a relatively common yet under-reported cause of systemic pruritus. It is a debilitating condition often associated with pain, which impairs the patient's quality of life. Although much literature exists about renal and hepatic pruritus, there is a dearth of information and awareness about neuropathic itch. The pathogenesis of neuropathic itch is complex and can result from an insult at any point along the itch pathway, ranging from the peripheral receptors and nerves until the brain. There are several causes of neuropathic itch, many of which do not produce any skin lesions and are thus, often missed. A detailed history and clinical examination are necessary for the diagnosis, while laboratory and radiologic investigations may be needed in select cases. Several therapeutic strategies currently exist involving both non-pharmacological and pharmacological measures, the latter including topical, systemic, and invasive options. Further research is ongoing to clarify its pathogenesis and to design newer targeted therapies with minimal adverse effects. This narrative review highlights the current understanding of this condition, focusing on its causes, pathogenesis, diagnosis, and management, along with newer investigational drugs.

Metameric pruritus as the sole manifestation of an intramedullary tumor in a toddler

An 18-month-old child presented with persistent pruritus and excoriation involving the right T9 and T10 dermatomes. She did not exhibit any other dermatological or neurological anomalies. Based on magnetic resonance imaging investigation of the spine, T8 ganglioglioma was diagnosed and surgically removed resulting in resolution of the pruritus within a few days. This observation underlines the importance of neuroimaging in patients presenting with metameric pruritus without specific skin lesions, especially in young children.

Psychogenic and neurogenic components in patients with psychogenic or neuropathic pruritus: PRURINEURO: A non-interventional single-centre prospective assay

Background

The causes of pruritus are multiple and commonly classified into six different categories: dermatological, systemic, neuropathic, psychogenic, mixed and idiopathic. In clinical practice, psychogenic and neurogenic mechanisms tend to be separated in the etiological diagnosis of neuropathic or psychogenic disorders; nevertheless, studies investigating the respective psychogenic and neurogenic components are lacking.

Objective

The main objective of this work was to highlight the differences and potential common characteristics between psychogenic pruritus and neuropathic pruritus.

Methods

This study was a noninterventional single-centre prospective assay. Patients with neuropathic (NP) or psychogenic (PP) pruritus were proposed to participate. The psychogenic and neurogenic components of pruritus in these patients were evaluated using six validated questionnaires or criteria, namely, the diagnosis criteria of psychogenic pruritus, the NP5 questionnaire, the Brest Pruritus Qualitative Assessment Questionnaire, Hospital Anxiety and Depression Scale, Toronto Alexithymia Scale, and DN4i.

Results

Twenty-five patients with NP and 15 with PP were included. A difference between the two groups was observed for NP5, with mean scores of 2.8 ± 0.9 and 1.4 ± 1 for the NP and PP groups, respectively (p < 0.0001). For depression, the average score was 3.5 ± 3.9 for the NP group and 7.5 ± 5.1 for the PP group (p < 0.02).

Conclusion

While neuropathic and psychogenic disorders are different diagnoses, neuropathic and psychogenic components may exist simultaneously in patients with NP or PP.

Alleviation of neuropathic pain with neuropeptide Y requires spinal Npy1r interneurons that coexpress Grp

Neuropeptide Y targets the Y1 receptor (Y1) in the spinal dorsal horn (DH) to produce endogenous and exogenous analgesia. DH interneurons that express Y1 (Y1-INs; encoded by Npy1r) are necessary and sufficient for neuropathic hypersensitivity after peripheral nerve injury. However, as Y1-INs are heterogenous in composition in terms of morphology, neurophysiological characteristics, and gene expression, we hypothesized that a more precisely defined subpopulation mediates neuropathic hypersensitivity. Using fluorescence in situ hybridization, we found that Y1-INs segregate into 3 largely nonoverlapping subpopulations defined by the coexpression of Npy1r with gastrin-releasing peptide (Grp/Npy1r), neuropeptide FF (Npff/Npy1r), and cholecystokinin (Cck/Npy1r) in the superficial DH of mice, nonhuman primates, and humans. Next, we analyzed the functional significance of Grp/Npy1r, Npff/Npy1r, and Cck/Npy1r INs to neuropathic pain using a mouse model of peripheral nerve injury. We found that chemogenetic inhibition of Npff/Npy1r-INs did not change the behavioral signs of neuropathic pain. Further, inhibition of Y1-INs with an intrathecal Y1 agonist, [Leu31, Pro34]-NPY, reduced neuropathic hypersensitivity in mice with conditional deletion of Npy1r from CCK-INs and NPFF-INs but not from GRP-INs. We conclude that Grp/Npy1r-INs are conserved in higher order mammalian species and represent a promising and precise pharmacotherapeutic target for the treatment of neuropathic pain.

Basic mechanisms of itch

Pruritus (or itch) is an unpleasant sensation leading to a desire to scratch. In the epidermis, there are selective C or Aδ epidermal nerve endings that are pruriceptors. At their other ends, peripheral neurons form synapses with spinal neurons and interneurons. Many areas in the central nervous system are involved in itch processing. Although itch does not occur solely because of parasitic, allergic, or immunologic diseases, it is usually the consequence of neuroimmune interactions. Histamine is involved in a minority of itchy conditions, and many other mediators play a role: cytokines (eg, IL-4, IL-13, IL-31, IL-33, and thymic stromal lymphopoietin), neurotransmitters (eg, substance P, calcitonin gene-related peptide, vasoactive intestinal peptide, neuropeptide Y, NBNP, endothelin 1, and gastrin-releasing peptide), and neurotrophins (eg, nerve growth factor and brain-derived neurotrophic factor). Moreover, ion channels such as voltage-gated sodium channels, transient receptor potential vanilloid 1, transient receptor ankyrin, and transient receptor potential cation channel subfamily M (melastatin) member 8 play a crucial role. The main markers of nonhistaminergic pruriceptors are PAR-2 and MrgprX2. A notable phenomenon is the sensitization to pruritus, in which regardless of the initial cause of pruritus, there is an increased responsiveness of peripheral and central pruriceptive neurons to their normal or subthreshold afferent input in the context of chronic itch.

Pruritus and brain tumours: A prospective and descriptive study

Background

Pruritus, especially localised to the nostrils, has been reported as a specific sign of brain tumours.

Objectives

The main goal of this study was to estimate the prevalence of pruritus in a group of patients with brain tumours. The second outcome was to better characterise this pruritus with a specific questionnaire and a skin examination.

Methods

From June 2020 to September 2021, all patients with a diagnosis of brain tumour were included in this prospective, monocentric study. If the patient suffered from pruritus, a dermatological examination was performed.

Results

Two hundred patients with brain tumours were included. Thirty-five of them suffered from pruritus (17.5%). Among them, 15 patients did not present with any skin disease, and 8 could have neuropathic pruritus according to the NP5 questionnaire. No patients presented with pruritus of the nostrils.

Discussion

This study did not show clear evidence of specifically localised pruritus induced by brain tumours.

Conclusion

Pruritus observed in patients with brain tumours seems not to be caused by the brain malignancies in most cases. The specific localization to the nostrils cannot be considered a specific marker.

Odevixibat: A Review of a Bioactive Compound for the Treatment of Pruritus Approved by the FDA

Odevixibat is synthesized through chemical modification of Benzothiazepine's structure. It is a tiny chemical that inhibits the ileal bile acid transporter and is used to treat a variety of cholestatic illnesses, including progressive familial intrahepatic cholestasis (PFIC). For cholestatic pruritus and liver disease development, bile acid transporter inhibition is a unique treatment strategy. Odevixibat reduces enteric bile acid reuptake. Oral odevixibat was also studied in children with cholestatic liver disease. Odevixibat received its first approval in the European Union (EU) in July 2021 for the treatment of PFIC in patients aged 6 months, followed by approval in the USA in August 2021 for the treatment of pruritus in PFIC patients aged 3 months. Bile acids in the distal ileum can be reabsorbed by the ileal sodium/bile acid cotransporter, a transport glycoprotein. Odevixibat is a sodium/bile acid co-transporter reversible inhibitor. An average 3 mg once-daily dose of odevixibat for a week resulted in a 56% reduction in the area under the curve of bile acid. A daily dose of 1.5 mg resulted in a 43% decrease in the area under the curve for bile acid. Odevixibat is also being evaluated in many countries for the treatment of other cholestatic illnesses, including Alagille syndrome and biliary atresia. This article reviews the updated information on odevixibat with respect to its clinical pharmacology, mechanism of action, pharmacokinetics, pharmacodynamics, metabolism, drug-drug interactions, pre-clinical studies, and clinical trials.

Role of GRPR in Acupuncture Intervention in the "Itch-scratch Vicious Cycle" Spinal Circuit of Chronic Pruritus

Many previous studies have shown the potential antipruritic effect of acupuncture. This paper reviews the antipruritic mechanisms of acupuncture according to these aspects: sample characteristics, detail of intervention, and effects evaluation. The majority of research on acupuncture's antipruritic effect has focused on primary afferents of the peripheral mechanism. Relatively few studies, however, have addressed the central mechanisms. Combination the latest research achievements of chronic itch, gastrin-releasing peptide receptor (GRPR) in the dorsal horn of the spinal cord may represent the first molecule identified that is dedicated to mediating the itch response and may provide an important therapeutic target for the treatment of chronic pruritic conditions. Therefore, GRPR may be a new target for acupuncture to relieve itch in the future and provide new ideas for acupuncture intervention in the mechanisms of the spinal level of the "itch-scratch vicious cycle" of chronic itch.

Successful treatment of notalgia paresthetica with lidocaine 5% medicated plaster: a case report

Notalgia paresthetica (NP) is a sensory neuropathy characterized by chronic, localized pruritus in a circumscribed area on the upper back. Pruritus, frequently resistant to treatment, may be accompanied by pain, paresthesia, allodynia and alloknesis. There is a paucity of data in the NP literature about the use of lidocaine 5% medicated plaster. This case involves a 75-year-old woman with NP and a history of many unsuccessful local or systemic treatments. The patient was treated with lidocaine 5% medicated plaster, while other therapies were progressively retired. After 11 weeks of therapy, a significant reduction in the intensity of itching was achieved and the itching area was reduced. The patient also reported an associated improvement in her quality of life throughout therapy. In conclusion, lidocaine 5% medicated plaster was successful in relieving itching and other symptoms in this case of NP.

Altered resting-state functional connectivity of default mode network in brachioradial pruritus

BACKGROUND

Patients with chronic pruritus (CP) have a low quality of life, thus it is important to gain a better understanding of the underlying processes. Previous functional magnetic resonance imaging studies at rest (rs-fMRI) have shown that mainly areas associated with the default mode network (DMN), sensorimotor (SMN), frontoparietal (FPN) and salience networks (SN) are involved in the processing of itch in patients with chronic pruritus (CP), as well as the cortico-striatal circuit, which is involved in the motoric preparation of scratching. rs-fMRI studies on functional connectivity (FC) patterns of resting-state networks (RSNs) in patients with inflammatory atopic dermatitis (AD) or with neuropathic brachioradial pruritus (BRP) compared to healthy controls (HC) are lacking.

OBJECTIVES

The main goals of this study were to investigate whether functional connectivity within networks and areas associated with itch detection and processing are altered in patients with AD and BRP compared to matched healthy controls by rsfMRI, respectively.

METHODS

Patients with AD (n = 28) and with BRP (n = 28) were compared to corresponding matched healthy controls by rsfMRI. Group specific RSNs were identified by independent component analysis (ICA) and between-group differences in the RSNs were analyzed by dual regression technique. Seed-based functional connectivity was analyzed in several itch-related brain regions belonging to the DMN, SN and FPN, respectively.

RESULTS

ICA and seed-based analyses revealed decreased functional connectivity in BRP compared to HC specially within the DMN including the precuneus and cingulate cortex. For AD patients in comparison to HC, as well as when BRP and AD patients when compared directly, no significant FC differences at rest were seen.

CONCLUSIONS

Our findings point towards decreased FC particularly in the DMN at rest in patients with BRP. These results seem to indicate that central connectivity patterns at rest differentially encode itch in BRP and AD.

In Vitro Sensitive Skin Models: Review of the Standard Methods and Introduction to a New Disruptive Technology

The skin is a protective organ, able to decode a wide range of tactile, thermal, or noxious stimuli. Some of the sensors belonging to the transient receptor potential (TRP) family, for example, TRPV1, can elicit capsaicin-induced heat pain or histamine-induced itching sensations. The sensory nerve fibers, whose soma is located in the trigeminal or the dorsal root ganglia, are able to carry signals from the skin’s sensory receptors toward the brain via the spinal cord. In some cases, in response to environmental factors, nerve endings might be hyper activated, leading to a sensitive skin syndrome (SSS). SSS affects about 50% of the population and is correlated with small-fiber neuropathies resulting in neuropathic pain. Thus, for cosmetical and pharmaceutical industries developing SSS treatments, the selection of relevant and predictive in vitro models is essential. In this article, we reviewed the different in vitro models developed for the assessment of skin and neuron interactions. In a second part, we presented the advantages of microfluidic devices and organ-on-chip models, with a focus on the first model we developed in this context.

Mechanisms and therapeutic targets for neuropathic itch

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

Dorsal horn volume loss and pain pathway changes in Cavalier King Charles Spaniels with syringomyelia, signs of pain, and phantom scratching

ABSTRACT

Central neuropathic pain is a core clinical sign of syringomyelia in humans and Cavalier King Charles Spaniel (CKCS) dogs. This histopathological study used spinal cords from CKCS with syringomyelia to investigate: 1) whether specific structural cervical spinal cord entities involved in nociception are affected by loss of neuroparenchyma or other pathological changes in CKCS with pain-related behaviour and phantom scratching, 2) if pain related behaviour or phantom scratching correlated with loss of a specific anatomical entity or upregulation of glia cells, and 3) if syringomyelia-related lesions affected specific functional spinal cord units of nociception.Spinal cord segments C1-C8 from CKCS with MRI-confirmed syringomyelia and clinical signs of pain and phantom scratch (n=8) were compared to CKCS without syringomyelia (n=4). Dogs with unilateral scratching (n=7) had a volume loss (P=0.043) of the dorsal horn laminae I-III in the ipsilateral side compared to the contralateral dorsal horn. A clear pattern of ipsilateral changes in the dorsal root entry zone characterised by deafferentation and reorganization of first-order axons into deeper laminae was found in cases with lateralised scratching. Significant changes in cell number density were not found for astrocytes or microglia, suggesting that the dogs represented cases of end-stage syringomyelia and thus could not reveal astrogliosis and microgliosis, which may be involved in the early phases of syrinx development and phantom scratch.The present relationship between clinical findings and dorsal horn and pain pathway pathology in CKCS suggests that these dogs may be of interest as a supplement to experimental model pain research.

Sensitive Skin Syndrome: A Low-Noise Small-Fiber Neuropathy Related to Environmental Factors?

Background and Objectives

Patients frequently complain of mild, transient, unpleasant skin sensations that cannot be diagnosed as common neuropathies. Dermatologists have termed these symptoms “sensitive skin syndrome.” This narrative review was performed for a better knowledge by other specialists.

Databases and Data Treatment

Publications on pain in sensitive skin syndrome were obtained from PubMed.

Results

There is a growing body of data supporting the concept that sensitive skin is a type of small-fiber neuropathy. The arguments are based on clinical data, a decrease in intra-epidermal nerve fiber density, quantitative sensory testing abnormalities and an association with irritable bowel syndrome and sensitive eyes. Sensitive skin is triggered by environmental factors. Sensitive skin is a frequent condition, with a lifetime prevalence of ~50% according to self-reports.

Conclusions

Mild levels of skin pain or itch are frequently experienced by patients, who rarely report them. There is a need for a better knowledge of sensitive skin because it can be the first level of small-fiber neuropathies.

Satellite Glial Cells and Neurons in Trigeminal Ganglia Are Altered in an Itch Model in Mice

Itch (pruritus) is a common chronic condition with a lifetime prevalence of over 20%. The mechanisms underlying itch are poorly understood, and its therapy is difficult. There is recent evidence that following nerve injury or inflammation, intercellular communications in sensory ganglia are augmented, which may lead to abnormal neuronal activity, and hence to pain, but there is no information whether such changes take place in an itch model. We studied changes in neurons and satellite glial cells (SGCs) in trigeminal ganglia in an itch model in mice using repeated applications of 2,4,6-trinitro-1-chlorobenzene (TNCB) to the external ear over a period of 11 days. Treated mice showed augmented scratching behavior as compared with controls during the application period and for several days afterwards. Immunostaining for the activation marker glial fibrillary acidic protein in SGCs was greater by about 35% after TNCB application, and gap junction-mediated coupling between neurons increased from about 2% to 13%. The injection of gap junction blockers reduced scratching behavior, suggesting that gap junctions contribute to itch. Calcium imaging studies showed increased responses of SGCs to the pain (and presumed itch) mediator ATP. We conclude that changes in both neurons and SGCs in sensory ganglia may play a role in itch.

Prescribing of Gabapentinoids with or without opioids after burn injury in the US, 2012-2018

Burn injury pain manifests as a combination of inflammatory, nociceptive, and neuropathic features. While opioids are the mainstay of burn pain management, non-opioid medications, such as gabapentinoids, have also been considered as they target the central nervous system. Increased opioid adverse events and overdose deaths in the United States led to the 2014 and 2016 guidelines to reduce opioid prescribing and consider alternatives, such as gabapentinoids. In the context of burn, the rate of gabapentinoid prescribing at the national level is unknown and it is unclear whether any shift has occurred in prescribing practices over time. We conducted a population level cohort study of adult burn patients from 2012 to 2018 to evaluate the rates and determinants of gabapentinoid prescribing, with and without opioids. Of 98,001 patients with burn, 22,521 (22.98%) received opioids and/or gabapentinoids (GABA). GABA represented 2.4% of prescriptions in 2012, but increased to 7.2% by 2018, while GABA-opioid co-prescriptions increased from 2.3% to 5.1%. The rate of increase in GABA prescriptions was higher for those aged 50-65 years or residing in the South. After adjustment, GABA was 44% more likely to be prescribed in 2017 and 2018 compared to 2012 and 2013, opioids were 38% less likely, while co-prescribing did not show a statistically significant change. Our study showed a modest increase in gabapentinoids' outpatient prescribing for burn patients after the 2014 and 2016 guidelines, indicating more opportunities for prescribers to expand non-opioid pain management in this population.

The Contribution of TSLP Activation to Hyperalgesia in Dorsal Root Ganglia Neurons of a Rat

Peripheral nerve injury involves divergent alterations within dorsal root ganglia (DRG) neurons sensitized by persistent inflammation. Thymic stromal lymphopoietin (TSLP) production is crucial in the development of chronic inflammatory responses. Herein, we investigate the changes of TSLP expression in rats’ DRG neurons between injured and uninjured sides in the same rat. Linalyl acetate (LA) was served as a TSLP inhibitor and given intraperitoneally. Rats were assigned to be group of chronic constriction injury (CCI) of the sciatic nerve and the group of CCI of the sciatic nerve administrated with LA. Over 14 days, the rats were measured for paw withdrawal thresholds. DRGs were collected to assess morphological changes via immunofluorescence study. After receiving CCI, the rats rapidly developed mechanical hyperalgesia. TSLP expression at DRG, on the ipsilateral injured side, was consistent with changes in pain behaviors. TSLP appeared in nerve fibers with both small diameters and large diameters. Additionally, TSLP was expressed mostly in transient receptor potential vanilloid-1 (TRPV1)-positive nociceptive neurons. Administration with LA can attenuate the pain behaviors and expression of TSLP in DRG neurons, and in apoptotic neurons at the injured side, but not in the contra-lateral uninjured side. Overall, these results imply that altered expressions of TSLP in nociceptive DRG neurons contributed to mechanical hyperalgesia in a CCI rat model.

The Role of Transient Receptor Potential A1 and G Protein-Coupled Receptor 39 in Zinc-Mediated Acute and Chronic Itch in Mice

Itching is a common symptom of many skin or systemic diseases and has a negative impact on the quality of life. Zinc, one of the most important trace elements in an organism, plays an important role in the regulation of pain. Whether and how zinc regulates itching is largely unclear. Herein, we explored the role of Zn²⁺ in the regulation of acute and chronic itch in mice. It is found that intradermal injection (i.d.) of Zn²⁺ dose-dependently induced acute itch and transient receptor potential A1 (TRPA1) participated in Zn²⁺-induced acute itch in mice. Moreover, the pharmacological analysis showed the involvement of histamine, mast cells, opioid receptors, and capsaicin-sensitive C-fibers in Zn²⁺-induced acute itch in mice. Systemic administration of Zn²⁺ chelators, such as N,N,N′,N′-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), pyrithione, and clioquinol were able to attenuate both acute itch and dry skin-induced chronic itch in mice. Quantitative polymerase chain reaction (Q-PCR) analysis showed that the messenger RNA (mRNA) expression levels of zinc transporters (ZIPs and ZnTs) significantly changed in the dorsal root ganglia (DRG) under dry skin-induced chronic itch condition in mice. Activation of extracellular signal-regulated kinase (ERK) pathway was induced in the DRG and skin by the administration of zinc or under dry skin condition, which was inhibited by systemic administration of Zn²⁺ chelators. Finally, we found that the expression of GPR39 (a zinc-sensing GPCR) was significantly upregulated in the dry skin mice model and involved in the pathogenesis of chronic itch. Together, these results indicated that the TRPA1/GPR39/ERK axis mediated the zinc-induced itch and, thus, targeting zinc signaling may be a promising strategy for anti-itch therapy.

Oncostatin M can sensitize sensory neurons in inflammatory pruritus

[Figure: see text].

Pruritus, Pain, and Depression Associated with the Most Common Skin Diseases: Data from the French Study "Objectifs Peau"

BACKGROUND

The prevalence and impact of pruritus, pain, and other sensory symptoms in skin diseases are poorly known.

OBJECTIVE

To assess the frequency of these symptoms with dermatoses and their association with depression using data from the "Objectifs Peau" survey.

METHODS

A representative sample of 20,012 French individuals was created using the usual quota method.

RESULTS

When patients suffered from both pruritus and skin pain, they had a higher relative risk of psychological suffering (2.9) than those who suffered only from pruritus (1.4) or skin pain (1.2). Pruritus was reported in 48.55% of patients with acne, 43.24% with mycoses, 44.35% with warts, and 36.51% with rosacea. For skin pain, the results were 11.22%, 27.59%, and 16.13% for atopic dermatitis, acne, and warts, respectively. Other unpleasant sensations, such as tingling or burning, were also frequently reported.

CONCLUSION

Pruritus, pain, or other sensory symptoms were found to be common not only in classic pruritic skin diseases but also in acne, rosacea, or warts. The association of pruritus and pain dramatically increased psychological suffering. These symptoms must be systematically searched for in patients, especially since new therapeutic possibilities are emerging for the symptomatic treatment of pruritus.

Chronic itch: emerging treatments following new research concepts

Until recently, itch pathophysiology was poorly understood and treatments were poorly effective in relieving itch. Current progress in our knowledge of the itch processing, the numerous mediators and receptors involved has led to a large variety of possible therapeutic pathways. Currently, inhibitors of IL-31, IL-4/13, NK₁ receptors, opioids and cannabinoids, JAK, PDE4 or TRP are the main compounds involved in clinical trials. However, many new targets, such as Mas-related GPCRs and unexpected new pathways need to be also explored.

Small Fiber Neuropathy in the Elderly

Small fiber neuropathy is common and prevalent in the elderly. The disease can be associated with many medical conditions. It often has a negative impact on quality of life due to painful paresthesia, dizziness, and sedative side effects of pain medications. Skin biopsy is the gold standard diagnostic test. Screening for associated conditions is important, because etiology-specific treatment can slow down disease progression and ameliorate symptoms. Adequate pain control can be challenging due to safety and tolerability of pain medications in the elderly. Treatment should be individualized with the goals of controlling underlying causes, alleviating pain, and optimizing daily function.

Pruritus in autoimmune connective tissue diseases

Pruritus is one of the most common and bothersome symptoms of skin disorders, and its clinical characteristics and related pathomechanisms have been well described in certain dermatologic conditions, such as atopic dermatitis and urticaria. Although pruritus is believed to be as common in cutaneous autoimmune connective tissue diseases (ACTDs) as in other inflammatory skin disorders, its true characteristics have not been elucidated either qualitatively or quantitatively. Pruritus is present in ACTDs with various prevalence rates, characteristics, and mechanisms depending on the disease types. Pruritus most frequently and severely affects the patients with dermatomyositis, in which itch is strongly correlated with disease activity and severity, thus increased itch could also indicate a disease flare. Patients with other ACTDs, including lupus erythematosus (LE), Sjögren syndrome (SS), morphea, and systemic sclerosis (SSc), also suffer from their fair share of pruritus. Unfortunately, the currently available treatments for ACTDs seem to have only limited and unsatisfactory effects to control pruritus. The extensive impact of pruritus on the patients’ quality of life (QOL) and functioning warrants more targeted and individualized approaches against pruritus in ACTDs. This review will address the prevalence, suggested pathogenesis based on currently available evidences, and potential treatment options of pruritus in various ACTDs of the skin.

Neuropathic Itch: Routes to Clinical Diagnosis

Neuropathic itch occurs due to damage of neurons of the peripheral or central nervous system. Several entities, including metabolic, neurodegenerative, orthopedic, infectious, autoimmune, malignant, and iatrogenic conditions, may affect the somatosensory system and induce neuropathic itch. Due to the complex nature of neuropathic itch, particularly concerning its clinical presentation and possible etiological factors, diagnostic work-up of this condition is challenging. A detailed medical history, especially in regard to the itch, and a comprehensive physical examination are relevant to detect characteristic signs and symptoms of neuropathic itch and to rule out other possible causes for chronic itch. Complementary diagnostic exams, especially laboratory tests, determination of the intraepidermal nerve fiber density via a skin biopsy and radiological examinations may be indicated to confirm the diagnosis of neuropathic itch and to identify underlying etiological factors. Functional assessments such as quantitative sensory testing, nerve conduction studies, evoked potentials, or microneurography may be considered in particular cases. This review article provides a comprehensive overview of the diagnostic work-up recommended for patients with neuropathic itch.

Pruriplastic Itch-A Novel Pathogenic Concept in Chronic Pruritus

The International Association for the Study of Pain (IASP) defined three descriptors for pain: nociceptive pain is “pain that arises from actual or threatened damage to non neural tissue and is due to the activation of nociceptors”; neuropathic pain is “pain caused by a lesion or disease of the somatosensory nervous system”; and nociplastic pain is “pain that arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain.” Based on clinical and pathophysiological arguments, a similar definition of “pruriplastic pruritus” should be made. Pruriplastic pruritus would include psychogenic pruritus, as well as some cases of pruritus ani, vulvar pruritus, sensitive skin or other poorly understood cases of pruritus. This new descriptor of itch could serve as systematic screening for altered pruriceptive function in patients who suffer from chronic itch and it may also help in defining better tailored treatment by identifying patients who are likely to respond better to centrally rather than to peripherally targeted therapies.

Pruritus in psoriasis and atopic dermatitis: current treatments and new perspectives

Psoriasis and atopic dermatitis (AD) are two common chronic inflammatory skin diseases. Although showing different etiology and clinical manifestations, patients with either disease suffer from low health-related quality of life due to pruritus (dermal itch). Recent studies have revealed that more than 85% of psoriasis patients suffer from pruritus, and it is also the dominating symptom of AD. However, as this is a non-life treating symptom, it was partly neglected for years. In this review, we focus on current findings as well as the impact and potential treatments of pruritus in these two skin diseases. We first distinguish the type of itch based on involved mediators and modulators. This clear delineation between the types of pruritus based on involved receptors and pathways allows for precise treatment. In addition, insights into recent clinical trials aimed to alleviate pruritus by targeting these receptors are presented. We also report about novel advances in combinatorial treatments, dedicated to the type of pruritus linked to a causal disease. Altogether, we suggest that only a focused treatment tailored to the primary disease and the underlying molecular signals will provide fast and sustained relief of pruritus associated with psoriasis or AD.

Google search trends for itch in Europe: a retrospective longitudinal study

BACKGROUND

Itch is a common symptom in the general population. Affected individuals often do not seek medical consultation and rely on Internet searches to obtain information regarding their itch.

OBJECTIVES

The aim of this study was to attain insights into common concerns of the general population regarding itch can by analysing itch-related Internet search behaviour.

METHODS

Google AdWords Keyword Planner was used to assess search volumes for itch-related terms in 15 European countries between September 2014 and August 2018. All identified keywords were qualitatively categorized. Itch-related terms were descriptively analysed and are shown as number of searches/100 000 inhabitants.

RESULTS

The search volume for the keyword 'itch' per 100 000 inhabitants was highest in Northern Europe, followed by Eastern, Central and Southern Europe. In 4/15 countries, itch was searched for more often in the autumn/winter months compared to in the spring/summer months. Most itch-related terms were related to dermatological conditions such as inflammatory skin diseases (e.g. psoriasis, atopic dermatitis), allergic or immunologic conditions (e.g. urticaria), and infectious diseases or infestations (e.g. scabies). In terms of body location, genitoanal itch dominated the searches. Symptoms and signs related to itch, possible non-dermatological aetiologies, and treatment options were also among the most searched terms.

CONCLUSIONS

These analyses provided for the first time insights into the search behaviour patterns related to itch across Europe. People from Northern and Eastern Europe are more likely to seek online information regarding itch. Causes for the itch, especially dermatological conditions, and genitoanal itch are the most important concerns for Internet users. This unconventional and inexpensive method identifies medical needs of people beyond the medical setting, including people who do not seek medical consultation. Accordingly, the data could be used to guide public health interventions and manage respective inhabitants' medical needs.

Mechanisms Underlying the Skin-Gut Cross Talk in the Development of IgE-Mediated Food Allergy

Immune-globulin E (IgE)-mediated food allergy is characterized by a variety of clinical entities within the gastrointestinal tract, skin and lungs, and systemically as anaphylaxis. The default response to food antigens, which is antigen specific immune tolerance, requires exposure to the antigen and is already initiated during pregnancy. After birth, tolerance is mostly acquired in the gut after oral ingestion of dietary proteins, whilst exposure to these same proteins via the skin, especially when it is inflamed and has a disrupted barrier, can lead to allergic sensitization. The crosstalk between the skin and the gut, which is involved in the induction of food allergy, is still incompletely understood. In this review, we will focus on mechanisms underlying allergic sensitization (to food antigens) via the skin, leading to gastrointestinal inflammation, and the development of IgE-mediated food allergy. Better understanding of these processes will eventually help to develop new preventive and therapeutic strategies in children.

Itch processing in the brain

Itch is a sensation defined as the urge to scratch. The central mechanisms of itch are being increasingly studied. These studies are usually based on experimental itch induction methods, which can be classified into the following categories: histamine-induced, induction by other non-histamine chemicals (e.g. cowhage), physically induced (e.g. electrical) and mentally induced (e.g. audio-visual). Because pain has been more extensively studied, some extrapolations to itch can be proposed and verified by experiments. Recent studies suggest that the itch-processing network in the brain could be disrupted in certain diseases. This disruption could be related to the implication of new regions or the exclusion of already engaged brain regions from itch-processing network in the brain.

Itching Caused by TRPV3 (Transient Receptor Potential Vanilloid-3) Activator Application to Skin of Burn Patients

Background and objectives: Postburn pruritus is a common complication of scars in burn patients. In our previous study, we discovered increased expression of TRPV3, TRPV4, and TRPA1. Among them, TRPV3, in particular, is predominantly expressed in the epidermis of the tissue of pruritic burn scars. We sought to evaluate the correlation between the expression of TRPV3 activators and itching after application of TRPV3 activator carvacrol over burn scars. Materials and Methods: Design: This was a double-blind clinical trial with non-randomized distribution. Setting: This study was performed in a hospital setting. Patients or participants: Patients with itching of burn scars (numerical rating scale (NRS), <3; n = 8; Group 1 and NRS, ≥3; n = 16, Group 2) and healthy volunteers (n = 18, Group 3) were included. Interventions: The investigational drug carvacrol (100%, 75%, and 50%) and control drug (10% ethanol) were applied over the scars using IQ Ultimate™ 1 × 1 cm chamber sheets. Main variables of interest: The presence of pruritus, erythema, edema, and other skin lesions was evaluated. The verbal NRS scores were also compared. Results: Carvacrol induced more itching in Group 2 than in Groups 1 and 3. In Group 2, 100%, 75%, and 50% carvacrol caused significantly more itching (NRS score, 5.18 ± 3.04, 5.18 ± 3.04, and 4.93 ± 2.96, respectively) than that in Group 1 (NRS score, 1.00 ± 1.80, 1.00 ± 1.80, and 1.00 ± 1.80, respectively) and Group 3 (NRS score, 2.38 ± 1.94, 1.27 ± 1.32, respectively). Conclusions: The TRPV3 activator carvacrol can cause itching if applied over burn scars. This study can help understand the mechanism and prognosis of post-burn itching and contribute to the development of its treatment.

The etiology of notalgia paresthetica: a descriptive study of 117 patients

BACKGROUND

Notalgia paresthetica (NP) is a neuropathic itching condition unilaterally localized in the midscapular area. It is a common but an underdiagnosed disease, and only a few studies investigating NP etiology with a limited number of patients have been reported in the literature.

OBJECTIVE

We aimed to evaluate the demographic, clinical, histopathological, neurological, and radiological findings of NP patients and investigate correlations between them and symptoms of NP to elucidate the etiology of NP.

METHODS

One hundred and seventeen consecutive patients diagnosed with NP were included and assessed in a multidisciplinary and prospective manner. We recorded demographic and clinical data and obtained a skin biopsy from the pruritic or hyperpigmented region. Pruritus severity was assessed by visual analogue scale (VAS). All patients were evaluated neurologically with magnetic resonance imaging.

RESULTS

The mean age of the patients was 47.08 ± 12.28 years. The disease was more common in females (87.2%). Statistical analysis revealed that VAS scores were independent of the age, gender, and skin type of the patient. We found no significant difference in VAS scores between NP patients with or without comorbidities. Vertebral pathologies detected by MRI and amyloid deposition revealed in histopathology were not among the main factors affecting VAS scores.

STUDY LIMITATION

Since consecutive patients enrolled into the study, we could not include equal number of male and female patients.

CONCLUSION

We found no correlation between symptom severity and findings from neurological and histopathological evaluations. Further microneurological studies should be carried out to elucidate the etiology of NP.

[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.

PAR2, Keratinocytes, and Cathepsin S Mediate the Sensory Effects of Ciguatoxins Responsible for Ciguatera Poisoning

Ciguatera fish poisoning is caused by the consumption of fish contaminated with ciguatoxins (CTXs). The most distressing symptoms are cutaneous sensory disturbances, including cold dysesthesia and itch. CTXs are neurotoxins known to activate voltage-gated sodium channels, but no specific treatment exists. Peptidergic neurons have been critically involved in ciguatera fish poisoning sensory disturbances. Protease-activated receptor-2 (PAR2) is an itch- and pain-related G protein‒coupled receptor whose activation leads to a calcium-dependent neuropeptide release. In this study, we studied the role of voltage-gated sodium channels, PAR2, and the PAR2 agonist cathepsin S in the cytosolic calcium increase and subsequent release of the neuropeptide substance P elicited by Pacific CTX-2 (P-CTX-2) in rat sensory neurons and human epidermal keratinocytes. In sensory neurons, the P-CTX-2‒evoked calcium response was driven by voltage-gated sodium channels and PAR2-dependent mechanisms. In keratinocytes, P-CTX-2 also induced voltage-gated sodium channels and PAR2-dependent marked calcium response. In the cocultured cells, P-CTX-2 significantly increased cathepsin S activity, and cathepsin S and PAR2 antagonists almost abolished P-CTX-2‒elicited substance P release. Keratinocytes synergistically favored the induced substance P release. Our results demonstrate that the sensory effects of CTXs involve the cathepsin S-PAR2 pathway and are potentiated by their direct action on nonexcitable keratinocytes through the same pathway.

Advances in Understanding the Initial Steps of Pruritoceptive Itch: How the Itch Hits the Switch

Pruritoceptive (dermal) itch was long considered an accompanying symptom of diseases, a side effect of drug applications, or a temporary sensation induced by invading pruritogens, as produced by the stinging nettle. Due to extensive research in recent years, it was possible to provide detailed insights into the mechanism of itch mediation and modulation. Hence, it became apparent that pruritus is a complex symptom or disease in itself, which requires particular attention to improve patients’ health. Here, we summarize recent findings in pruritoceptive itch, including how this sensation is triggered and modulated by diverse endogenous and exogenous pruritogens and their receptors. A differentiation between mediating pruritogen and modulating pruritogen seems to be of great advantage to understand and decipher the molecular mechanism of itch perception. Only a comprehensive view on itch sensation will provide a solid basis for targeting this long-neglected adverse sensation accompanying numerous diseases and many drug side effects. Finally, we identify critical aspects of itch perception that require future investigation.

Prevalence and Severity of Dermatological Condition-Associated Skin Pain in the Chinese

BACKGROUND/AIM

Although the characteristics of cutaneous sensory symptoms in the general population have been documented, dermatological condition-associated skin pain has not been characterized yet. In the present study, we aimed to characterize dermatological condition-associated skin pain in the Chinese.

SUBJECTS AND METHODS

A questionnaire was given to outpatients to identify self-proclaimed skin pain at our dermatology clinic. The severity of skin pain was assessed using pain scale 0-10. Prevalence and pain severity were compared between males and females.

RESULTS

A total of 2144 patients, including 1254 females and 890 males aged 13-94 years, were included in this study. The overall prevalence of skin pain was 9.93% in this cohort. The prevalence of skin pain varied greatly with dermatological conditions (p<0.0001). Moreover, a higher prevalence of skin pain was observed in males than in females (p<0.05). Among the dermatological conditions reported, higher skin pain scales were found in subjects with either glucocorticoid-induced dermatitis (4.20 ± 0.73) or herpes zoster (4.00 ± 0.29). While the overall pain scales were comparable between males and females (2.38 ± 0.13 versus 2.68 ± 0.13), pain scales in patients with eczematous dermatitis were higher in females than in males (p<0.05). Furthermore, pain scales correlated positively with age. However, pain scales did not differ between subjects with versus without a family history of cutaneous sensory symptoms. These results demonstrate that the prevalence and severity of dermatological condition-associated skin pain vary with dermatological conditions and gender in the Chinese.

CONCLUSION

Patients with some dermatological conditions may experience skin pain. Although the pain is moderate, it can negatively impact the quality of patients' lives. Alleviation of skin pain should be considered when treating patients with certain dermatological conditions.

Chronic nodular prurigo: clinical profile and burden. A European cross-sectional study

BACKGROUND

Chronic nodular prurigo (CNPG) is a condition characterized by chronic itch, a prolonged scratching behaviour and the presence of pruriginous nodules. A comprehensive understanding of this condition, especially regarding its clinical characteristics and impact on quality of life is still lacking.

OBJECTIVES

Aim of this pan-European multicentre cross-sectional study was to establish the clinical profile of CNPG, including its associated burden.

METHODS

Fifteen centres from 12 European countries recruited CNPG patients presenting at the centre or using the centres' own databases. Patients were asked to complete a questionnaire in paper or electronic format. Demography, current co-morbidities, underlying disease, itch intensity, additional sensory symptoms, quality of life, highest burden and emotional experience of itch were assessed.

RESULTS

A total of 509 patients (210 male, median age: 64 years [52; 72]) were enrolled. Of these, 406 reported itch and CNPG lesions in the previous 7 days and qualified to complete the whole questionnaire. We recorded moderate to severe worst itch intensity scores in the previous 24 h. Scores were higher in patients with lower educational levels and those coming from Eastern or Southern Europe. Most patients experience itch often or always (71%) and report that their everyday life is negatively affected (53%). Itch intensity was considered to be the most burdensome aspect of the disease by 49% of the patients, followed by the visibility of skin lesions (21%) and bleeding of lesions (21%). The majority of patients was unaware of an underlying condition contributing to CNPG (64%), while psychiatric diseases were the conditions most often mentioned in association with CNPG (19%).

CONCLUSIONS

This multicentre cross-sectional study shows that itch is the dominant symptom in CNPG and reveals that the profile of the disease is similar throughout Europe.

Generalized chronic itch induced by small-fibre neuropathy: clinical profile and proposed diagnostic criteria

BACKGROUND

Small-fibre neuropathy (SFN) is a known cause for pain, however, it may be also associated with chronic itch. The clinical profile of chronic itch due to SFN is poorly defined and accordingly under-diagnosed in clinical care.

OBJECTIVES

To establish the clinical profile of patients with SFN and to propose diagnostic criteria for this patient population.

METHODS

Clinical data from patients diagnosed with SFN [chronic generalized itch and reduced intraepidermal nerve fibre density (IENFD)] were analysed retrospectively.

RESULTS

A total of 142 patients (60 females, median age: 62.5 years) were included. Patients reported daily, moderate to severe itch intensity scores occurring mostly in attacks (62.5%). Only 11 patients experienced exclusively itch, while the remaining patients (92%) reported pruralgia (itch along with painful sensations). Burning (50%), a sensation like needle pricks (46%) and tingling (45%) were the sensory symptoms reported by most patients. Cold or ice application led to an alleviation of the symptoms. The IENFD did not correlate with itch intensity; however, patients with a severely reduced IENFD (<30% of the normative cut-off value) reported more frequently sharp, spiky and drilling sensations compared to the remaining patients. The quality of life was moderately impaired and correlated with itch intensity, whereas anxiety and depression scores were low.

CONCLUSIONS

Onset of pruralgia on normal appearing skin, occurrence in attacks and symptomatic alleviation with cold/ice application should alert physicians for a possible neuropathic SFN-related origin of itch. A reduced IENFD can confirm the diagnosis of SFN.