New aspects of itch pathophysiology: component analysis of atopic itch using the 'Eppendorf Itch Questionnaire'

[Assessment of pruritus - current standards and implications for clinical practice : consensus paper of the Action Group Pruritus Parameter of the International Working Group on Pruritus Research (AGP)]

With a prevalence of 20%, chronic pruritus is a symptom of many diseases with major impact on healthcare costs. The lack of specific therapeutic measures makes the development of new drugs and their testing in clinical trials urgent. It is not possible to measure pruritus in an objective way. For these reasons, it is necessary to have a series of standardized measures to characterize pruritus in a reliable way. Intensity scales such as the visual analog scale (VAS) are most frequently used to document the course of the symptoms. However, for assessing pruritus intensity, VAS is not an optimal instrument, although it cannot be dispensed with. The VAS should be combined with other scales in clinical studies in order to internally test the consistency of data. Other instruments for assessing intensity and course of pruritus are in the process of development. Presently scratch activity and scratch-associated lesions can be documented in a descriptive fashion. There are some studies that have employed devices to document scratch activity; however, methodological studies are not yet available. The patient-benefit index is an indispensable tool in clinical trials. A questionnaire for gathering data on the history and some pruritus-specific parameters has been developed and published. Questionnaires on patient quality of life, anxiety and depression are helpful in obtaining data on other cost-relevant parameters. A questionnaire on the quality of life, for instance, can provide important help in the assessment of the burden of the disease. The results of these questionnaires can be correlated with data on pruritus intensity scales. The relevant questionnaires have been partially digitalized so that they are available immediately as part of patient care. Additional methodological developments and studies are required in order to define a robust set of instruments for measuring pruritus in daily practice and in clinical studies.

Pathogenesis and management of pruritus in cholestatic liver disease

Patients with cholestatic liver diseases such as primary biliary cirrhosis, primary sclerosing cholangitis and intrahepatic cholestasis of pregnancy commonly complain of pruritus. The underlying pathogenesis remains obscure with several mediators possibly playing an important role; these include lysophosphatidic acid, bile salts, opioids, histamine and progesterone metabolites. We describe in this review novel insights into the pathogenesis and management of pruritus in patients with cholestasis.

Chronic pruritus--more than a symptom: a qualitative investigation into patients' subjective illness perceptions

AIM

This article is a report of a study exploring the subjective illness perceptions of patients with chronic pruritus (>6 weeks).

BACKGROUND

Pruritus is a common symptom of dermatological as well as other conditions. This pervasive symptom has a substantial impact on quality of life. Little is known about how patients with chronic pruritus construct the symptom, what causes they ascribe, consequences they endure, how they control the symptom and experience the healthcare system.

DESIGN

A qualitative design taking a constructivist inquiry perspective.

METHODS

Semi-structured interviews with 16 patients were conducted between September 2008-February 2009 and analysed by qualitative content analysis.

RESULTS

Many patients find it very difficult to adequately describe the symptom to others resulting sometimes in bizarre accounts of the symptom that provoke irritation in lay people and health professionals. This irritation frequently leaves the sufferer feeling misunderstood. Patients often feel their burden is not taken seriously by health professionals. This and various other reasons contribute to difficulties in accepting a given diagnosis. This can leave patients unsatisfied with their current health care and the system. They respond with frequent doctor changes and consideration of complementary and alternative therapeutic methods.

CONCLUSION

Assisting patients with chronic pruritus in their efforts to adequately describe the symptom along with unconditional regard and empathy are key factors that can help enhance the provider-patient relationship and subsequent acceptance of a given diagnosis. A stronger emphasis on the perspectives of these patients may also improve the quality of healthcare provision.

Acupuncture compared with oral antihistamine for type I hypersensitivity itch and skin response in adults with atopic dermatitis: a patient- and examiner-blinded, randomized, placebo-controlled, crossover trial

BACKGROUND

Itch is the major symptom of atopic dermatitis (AD). Acupuncture has been shown to exhibit a significant effect on experimental itch in AD. Our study evaluated acupuncture and antihistamine itch therapy (cetirizine) on type I hypersensitivity itch and skin reaction in AD using a patient and examiner-blinded, randomized, placebo-controlled, crossover trial.

METHODS

Allergen-induced itch was evaluated in 20 patients with AD after several interventions in separate sessions: preventive (preceding) and abortive (concurrent) verum acupuncture (VAp and VAa), cetirizine (10 mg, VC), corresponding placebo interventions (preventive, PAp, and abortive, PAa, placebo acupuncture; placebo cetirizine pill, PC) and a no-intervention control (NI). Itch was induced on the forearm and temperature modulated over 20 min, using our validated model. Outcome parameters included itch intensity, wheal and flare size and the D2 attention test.

RESULTS

Mean itch intensity (SE: 0.31 each) was significantly lower following VAa (31.9) compared with all other groups (PAa: 36.5; VC: 36.8; VAp: 37.6; PC: 39.8; PAp: 39.9; NI: 45.7; P < 0.05). There was no significant difference between VAp and VC (P > 0.1), although both therapies were significantly superior to their respective placebo interventions (P < 0.05). Flare size following VAp was significantly smaller (P = 0.034) than that following PAp. D2 attention test score was significantly lower following VC compared with all other groups (P < 0.001).

CONCLUSIONS

Both VA and cetirizine significantly reduced type I hypersensitivity itch in patients with AD, compared with both placebo and NI. Timing of acupuncture application was important, as VAa had the most significant effect on itch, potentially because of counter-irritation and/or distraction. Itch reduction following cetirizine coincided with reduced attention.

Psychoneuroimmunology of psychological stress and atopic dermatitis: pathophysiologic and therapeutic updates

Atopic dermatitis is a chronic inflammatory skin disease characterized by impaired epidermal barrier function, inflammatory infiltration, extensive pruritus and a clinical course defined by symptomatic flares and remissions. The mechanisms of disease exacerbation are still poorly understood. Clinical occurrence of atopic dermatitis is often associated with psychological stress. In response to stress, upregulation of neuropeptide mediators in the brain, endocrine organs, and peripheral nervous system directly affect immune and resident cells in the skin. Lesional and non-lesional skin of patients with atopic dermatitis demonstrates increased mast cells and mast cell-nerve fiber contacts. In the setting of stress, sensory nerves release neuromediators that regulate inflammatory and immune responses, as well as barrier function. Progress towards elucidating these neuroimmune connections will refine our understanding of how emotional stress influences atopic dermatitis. Moreover, psychopharmacologic agents that modulate neuronal receptors or the amplification circuits of inflammation are attractive options for the treatment of not only atopic dermatitis, but also other stress-mediated inflammatory skin diseases.

Itch: association with chronic venous disease, pain, and quality of life

PURPOSE

The purpose of the study was to examine the symptom of itch and its relationship with chronic venous disease, pain, and quality of life.

DESIGN

The study used an exploratory, cross-sectional design.

METHODS

One hundred and sixty-one participants completed demographic, health, substance abuse, itch, and pain questionnaires and the SF-12v2 Health Survey to measure health related quality of life.

RESULTS

Participants were mostly men (n=95, 59%), African American (113, 70.2%), and had a mean age of 44.19 years. A history of injection drug use was reported by 91.4%. Using the clinical score of the Clinical-Etiology-Anatomy-Pathophysiology (CEAP) Classification of the worst leg, the most common classification was Class 3, edema without skin changes (45.9%); 18.6% had severe venous disease (Classes 5 and 6). Eighty-eight participants (54.7%) reported itch somewhere on their body with 74 of them (45.9%) reporting itch on the legs or feet. Fourteen participants who reported itch of their legs or feet had wounds on the legs or feet. A positive correlation between magnitude of reported itch and CEAP clinical classification was noted (0.26, P =.025). This relationship was not strictly linear with itch increasing at a faster rate at higher levels of the CEAP classification. Persons with leg or feet itch had poorer health related quality of life, more comorbidities, and higher leg pain than those without itch. Because the SF-12v2 Health Survey is norm based, persons with itch were more than 1 standard deviation below the mean for the United States for their mental and physical health scores.

CONCLUSIONS

Itch on the legs or feet is a clinically relevant problem that is related to the level of venous disease. Persons with lower extremity itch have higher pain ratings and lower quality of life.

Influence of acupuncture on type I hypersensitivity itch and the wheal and flare response in adults with atopic eczema - a blinded, randomized, placebo-controlled, crossover trial

BACKGROUND

Itch is a major symptom of allergic skin disease. Acupuncture has been shown to exhibit a significant effect on histamine-induced itch in healthy volunteers. We investigated the effect of acupuncture on type I hypersensitivity itch and skin reaction in a double-blind, randomized, placebo-controlled, crossover trial.

METHODS

An allergen stimulus (house dust mite or grass pollen skin prick) was applied to 30 patients with atopic eczema before (direct effect) and after (preventive effect) two experimental approaches or control observation: acupuncture at points Quchi and Xuehai [verum acupuncture (VA), dominant side], 'placebo-point' acupuncture (PA, dominant side), no acupuncture (NA). Itch intensity was recorded on a visual analogue scale. After 10 min, wheal and flare size and skin perfusion (via LASER-Doppler) were measured at the stimulus site, and the validated Eppendorf Itch Questionnaire (EIQ) was answered.

RESULTS

Mean itch intensity was significantly lower in VA (35.7 +/- 6.4) compared to NA (45.9 +/- 7.8) and PA (40.4 +/- 5.8) regarding the direct effect; and significantly lower in VA (34.3 +/- 7.1) and PA (37.8 +/- 5.6) compared to NA (44.6 +/- 6.2) regarding the preventive effect. In the preventive approach, mean wheal and flare size were significantly smaller in VA (0.38 +/- 0.12 cm(2)/8.1 +/- 2.0 cm(2)) compared to PA (0.54 +/- 0.13 cm(2)/13.5 +/- 2.8 cm(2)) and NA (0.73 +/- 0.28 cm(2)/15.1 +/- 4.1 cm(2)), and mean perfusion in VA (72.4 +/- 10.7) compared to NA (84.1 +/- 10.7). Mean EIQ ratings were significantly lower in VA compared to NA and PA in the treatment approach; and significantly lower in VA and PA compared to NA in the preventive approach.

CONCLUSIONS

Acupuncture at the correct points showed a significant reduction in type I hypersensitivity itch in patients with atopic eczema. With time the preventive point-specific effect diminished with regard to subjective itch sensation, whereas it increased in suppressing skin-prick reactions.

Temperature modulated histamine-itch in lesional and nonlesional skin in atopic eczema - a combined psychophysical and neuroimaging study

BACKGROUND

Itch is the major symptom of many allergic diseases; yet it is still difficult to measure objectively. The aim of this study was to use an evaluated itch stimulus model in lesional (LS) and nonlesional (NLS) atopic eczema (AE) skin and to characterize cerebral responses using functional magnetic resonance imaging (fMRI).

METHODS

Thermal modulation was performed on a histamine stimulus in randomized order on LS or NLS in rapid alternating order from 32 degrees C (warm) to 25 degrees C (cold). Subjective itch ratings were recorded. Additionally, fMRI measurements were used to analyze the cerebral processing (n = 13). Healthy skin (HS) of age-matched volunteers served as control (n = 9).

RESULTS

Mean VAS itch intensity was significantly (P < 0.0001) higher during the relative cold [55.2 +/- 8.3% (LS); 48.6 +/- 8.2% (NLS)] compared to the relative warm blocks [36.0 +/- 7.3% (LS); 33.7 +/- 7.6% (NLS)]. Compared to HS, the itch response was delayed in LS and NLS. Itch intensity was perceived highest in LS, followed by NLS and HS. For NLS, fMRI revealed at the beginning of the itch provocation a cerebral deactivation pattern in itch processing structures (thalamus, prefrontal, cingulate, insular, somatosensory and motor cortex). During the course of stimulation, the cerebral deactivation was reduced with time and instead an activation of the basal ganglia occurred. In contrast LS showed an activation instead of deactivation pattern already at the beginning of the stimulation in the above mentioned structures.

CONCLUSIONS

Moderate short-term temperature modulation led to a reproducible, significant enhancement of histamine-induced itch with the strongest effect in LS. The differences in itch perception and itch kinetics between healthy volunteers and NLS in patients point towards an ongoing central inhibitory activity patients with AE, especially at the beginning of the itch provocation.

The 5-D itch scale: a new measure of pruritus

BACKGROUND

Itching is a subjective and multidimensional experience which is difficult to quantify. Most methodologies to assess itching suffer from being unidimensional, for example only measuring intensity without impact on quality of life, or only measuring scratching activity. None has actually been demonstrated to be able to detect change over time, which is essential to using them as an outcome measure of response to an intervention. The 5-D itch scale was developed as a brief but multidimensional questionnaire designed to be useful as an outcome measure in clinical trials. The five dimensions are degree, duration, direction, disability and distribution.

OBJECTIVES

To study the 5-D with respect to validity, reliability and response to change.

METHODS

The 5-D was administered to 234 individuals with chronic pruritus due to liver disease (n = 63), kidney disease (n = 36), dermatological disorders (n = 56), HIV/AIDS (n = 28) and burn injuries (n = 51). The 5-D was administered at baseline and after a 6-week follow-up period. A subset of 50 untreated patients was retested after 3 days to assess test-retest reliability.

RESULTS

The 5-D score correlated strongly with a visual analogue score: r = 0.727 at baseline (P < 0.0001), r = 0.868 at the 3-day repeat (P < 0.0001), and r = 0.892 at the 6-week follow-up (P < 0.0001). There was no change in mean 5-D score between day 1 and day 3 in untreated individuals (intraclass correlation coefficient = 0.96, P < 0.0001). The 5-D did, however, detect significant changes in pruritus over the 6-week follow-up period (P < 0.0001). Subanalysis of the different patient groups revealed similar response patterns and scores, with the exception of lower total scores for the burn victims due to lower scores on the distribution domain because they itched only at the site of their burn.

CONCLUSIONS

The 5-D, therefore, is a reliable, multidimensional measure of itching that has been validated in patients with chronic pruritus to able to detect changes over time. The 5-D should be useful as an outcome measure in clinical trials.

Pathogenesis and treatment of pruritus in cholestasis

Pruritus is an enigmatic, seriously disabling symptom accompanying cholestatic liver diseases and a broad range of other disorders. Most recently, novel itch-specific neuronal pathways, itch mediators and their relevant receptors have been identified. In addition, new antipruritic therapeutic strategies have been developed and/or are under evaluation. This review highlights recent experimental and clinical findings focusing on the pathogenesis and actual treatment of pruritus in cholestatic liver disease. Evidence-based therapeutic recommendations, including the use of anion exchange resins cholestyramine, colestipol and colesevelam, the microsomal enzyme inducer rifampicin, the opioid receptor antagonists naltrexone and naloxone, and the serotonin reuptake inhibitor sertraline, are provided.

Urinary eosinophil-derived neurotoxin concentrations in patients with atopic dermatitis: a useful clinical marker for disease activity

BACKGROUND

It has been reported that measurements of eosinophil-derived neurotoxin (EDN) may be useful for identifying eosinophil activities in allergic diseases including atopic dermatitis.

METHODS

EDN concentrations in the urine were measured by enzyme-linked immunosorbent assay, and the number of eosinophils in the peripheral blood was counted in 30 patients with atopic dermatitis. The severity of atopic dermatitis was graded on the criteria proposed by Rajka and Langeland. The disease activity was assessed by each patient on a visual analogue scale (VAS).

RESULTS

Urinary concentrations of EDN in patients with atopic dermatitis showed a significant positive correlation with disease severity. Urine EDN concentrations also correlated with VAS scores for itching, skin condition, overall skin symptoms and total VAS score, but not with the VAS score for skin dryness. Urinary EDN concentrations did not correlate with the number of eosinophils in the peripheral blood.

CONCLUSIONS

The urinary EDN concentration in patients with atopic dermatitis is a useful clinical marker for monitoring disease activity.

TRP channels as novel players in the pathogenesis and therapy of itch

Itch (pruritus) is a sensory phenomenon characterized by a (usually) negative affective component and the initiation of a special behavioral act, i.e. scratching. Older studies predominantly have interpreted itch as a type of pain. Recent neurophysiological findings, however, have provided compelling evidence that itch (although it indeed has intimate connections to pain) rather needs to be understood as a separate sensory modality. Therefore, a novel pruriceptive system has been proposed, within which itch-inducing peripheral mediators (pruritogens), itch-selective receptors (pruriceptors), sensory afferents and spinal cord neurons, and defined, itch-processing central nervous system regions display complex, layered responses to itch. In this review, we begin with a current overview on the neurophysiology of pruritus, and distinguish it from that of pain. We then focus on the functional characteristics of the large family of transient receptor potential (TRP) channels in skin-coupled sensory mechanisms, including itch and pain. In particular, we argue that - due to their expression patterns, activation mechanisms, regulatory roles, and pharmacological sensitivities - certain thermosensitive TRP channels are key players in pruritus pathogenesis. We close by proposing a novel, TRP-centered concept of pruritus pathogenesis and sketch important future experimental directions towards the therapeutic targeting of TRP channels in the clinical management of itch.

Psychosomatic cofactors and psychiatric comorbidity in patients with chronic itch

BACKGROUND

While psychosomatic factors may be involved in eliciting as well as coping with chronic itch, psychiatric comorbidity often goes unrecognized in dermatological patients.

AIM

To record psychiatric illness, psychiatric and psychotherapeutic pretreatment, and psychotherapy indication in dermatology inpatients with pruritus.

METHODS

A consecutive sample of 109 dermatology inpatients with the symptom of pruritus were examined by interviews with consecutive ratings by experts (using psychiatric ICD-10 diagnoses, the Global Assessment of Functioning Scale and the Impairment Score) and self-assessment using the the Eppendorf Itch Questionnaire.

RESULTS

In > 70% of the pruritus patients, 1-6 psychiatric diagnoses could be demonstrated. In > 60%, psychotherapeutic or psychiatric treatment was recommended. In contrast, almost 90% of the patients had had no previous psychotherapeutic experience.

CONCLUSION

As psychiatric comorbidity in dermatology inpatients suffering from chronic itch is high, dermatology departments should aim for an improvement of their psychosomatic consultation and liaison services.

Itch Severity Scale: a self-report instrument for the measurement of pruritus severity

BACKGROUND

Assessing pruritus severity is difficult because of its subjective nature. A questionnaire that takes into account how the symptom is perceived by the patient may provide a more accurate representation of the pruritus. However, recently developed questionnaires do not specifically quantify severity of the symptom.

OBJECTIVES

To develop a self-report questionnaire to measure pruritus severity and to provide initial evidence of its validity and reliability.

METHODS

We modified a previously developed interview for the characterization and evaluation of pruritus, which was completed along with the RAND-36 Health Status Inventory and Dermatology Life Quality Index by patients with psoriasis-associated pruritus. Exploratory factor analysis, studies of internal consistency, and correlation analyses with health-related quality of life scores were used to help determine which components of the modified pruritus interview to include in the new questionnaire, the Itch Severity Scale (ISS). The ISS was then assessed for construct validity, internal consistency reliability and test-retest reliability.

RESULTS

Seven of the initial 11 components of the modified pruritus interview were included in the ISS. ISS scores correlated moderately with physical (r=-0 x 483) and mental (r=-0 x 492) health composite scores of the RAND-36 and strongly with Dermatology Life Quality Index scores (r=0 x 628), evidence of construct validity. It had an internal consistency reliability of 0 x 80 and a test-retest reliability of 0 x 95.

CONCLUSIONS

Based on this preliminary evidence of validity and reliability, this new seven-item ISS may be useful in comparing pruritus severity among different disease populations or in assessing pruritus treatment effectiveness.

Short-Term Alternating Temperature Enhances Histamine-Induced Itch: A Biphasic Stimulus Model

Itch is the major symptom of many allergic or inflammatory skin diseases; yet it is still difficult to measure objectively. Human studies on the physiology and pathophysiology of the itch sensation (e.g. functional magnetic resonance imaging studies) have been hampered by the lack of an efferent and manageable "on-off" stimulus. Here, a short-term temperature-modulated human histamine itch model is presented. In nine healthy right-handed male volunteers (age 29+/-2.6 years), 1% histamine dihydrochloride was used in the skin prick model as standard itch stimulus on the right forearm with subsequent thermal modulation of the target skin area using a Medoc TSA II NeuroSensory Analyzer thermode. Modulation occurred in rapid alternating order from 32 degrees C (neutral) to 25 degrees C (slight cold) and vice versa; each temperature block lasted 20 seconds. Subjective itch ratings were recorded using a computerized visual analog scale (VAS) and - for qualitative assessment - the Eppendorf Itch Questionnaire (EIQ). All subjects reported localized itch sensations without pain; mean VAS itch intensity was 50.6+/-3.5% during the 25 degrees C blocks and 33.8+/-3.9% during the 32 degrees C blocks (P<0.0001). Also, mean EIQ ratings were significantly higher related to the 25 degrees C blocks. In spite of the common knowledge that intensive cold can inhibit itch sensation, a reproducible, significant enhancement of histamine-induced itch by short-term moderate temperature decrease could be shown. This effect might be explained by peripheral and central adaptation processes triggered by alternating afferent activity patterns and might be used - owing to its "on/off" characteristics-in future itch physiology studies such as functional magnetic resonance imaging.

Neuronal Control of Skin Function: The Skin as a Neuroimmunoendocrine Organ

This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.

Pruritus as a leading symptom: clinical characteristics and quality of life in German and Ugandan patients

BACKGROUND

Pruritus is the most frequent and distressing symptom associated with dermatoses and various internal and neurological diseases.

OBJECTIVES

To investigate two different populations of patients with pruritus, one in Germany and one in Uganda, with a particular focus on clinical characteristics, aetiology and quality of life.

METHODS

We investigated by questionnaire 132 patients (59 men, 73 women, mean age 54.5 years) who were referred to the Department of Dermatology at the University Hospital of Magdeburg, Germany, with the diagnosis of pruritus as a leading symptom. The questionnaire was also applied in 84 patients who consulted the Dermatology Clinic at Mbarara, Uganda for pruritus. The questions referred to personal data and disease history of the individual, history and present occurrence of concomitant diseases, present and past therapy, quality, frequency and triggers of itching and scratching, other disorders and complaints, quality of life and impact on work and disability.

RESULTS

Seventy-five (57%) of the German patients had pruritus due to dermatoses, 47 patients (36%) had pruritus due to a systemic disease and in 10 patients (8%) pruritus was of unknown origin. Most had a history of pruritus of several months up to years. Pruritus associated with dermatoses mostly affected the whole body and was permanent with an undulatory character. Affective reactions such as aggression and depression occurred more frequently in dermatological patients compared with those with systemic pruritus. The former group felt that pruritus had a greater impact on their lives. Almost all Ugandan patients had pruritus due to dermatoses except for three patients with pruritus of unknown origin. Eczema and prurigo were the most frequently observed dermatoses in both German and Ugandan patients. Patients with pruritus in both populations showed an impaired quality of life. There was no pronounced difference between the populations with regard to feelings of depression and suicidal thoughts.

CONCLUSIONS

A great deal of helpful information in this complex group of patients can be obtained using this questionnaire. Pruritus has a major impact on quality of life and especially impairs those patients with pruritus associated with dermatoses and pruritus of unknown origin.

The neurobiology of itch

The neurobiology of itch, which is formally known as pruritus, and its interaction with pain have been illustrated by the complexity of specific mediators, itch-related neuronal pathways and the central processing of itch. Scratch-induced pain can abolish itch, and analgesic opioids can generate itch, which indicates an antagonistic interaction. However, recent data suggest that there is a broad overlap between pain- and itch-related peripheral mediators and/or receptors, and there are astonishingly similar mechanisms of neuronal sensitization in the PNS and the CNS. The antagonistic interaction between pain and itch is already exploited in pruritus therapy, and current research concentrates on the identification of common targets for future analgesic and antipruritic therapy.

Frontiers in pruritus research: scratching the brain for more effective itch therapy

This Review highlights selected frontiers in pruritus research and focuses on recently attained insights into the neurophysiological, neuroimmunological, and neuroendocrine mechanisms underlying skin-derived itch (pruritogenic pruritus), which may affect future antipruritic strategies. Special attention is paid to newly identified itch-specific neuronal pathways in the spinothalamic tract that are distinct from pain pathways and to CNS regions that process peripheral pruritogenic stimuli. In addition, the relation between itch and pain is discussed, with emphasis on how the intimate contacts between these closely related yet distinct sensory phenomena may be exploited therapeutically. Furthermore, newly identified or unduly neglected intracutaneous itch mediators (e.g., endovanilloids, proteases, cannabinoids, opioids, neurotrophins, and cytokines) and relevant receptors (e.g., vanilloid receptor channels and proteinase-activated, cannabinoid, opioid, cytokine, and new histamine receptors) are discussed. In summarizing promising new avenues for managing itch more effectively, we advocate therapeutic approaches that strive for the combination of peripherally active antiinflammatory agents with drugs that counteract chronic central itch sensitization.

Chronic itch and pain--similarities and differences

Both, pruritus and pain are aversive, but clearly distinct sensations originating in the peripheral and central nervous system. During the last years, many interactions between itch and pain in acute transmission and sensitization processes have been identified. It is common experience that the itch sensation can be reduced by the painful sensations caused by scratching. Vice versa analgesia may reduce this inhibition and thus enhance itch. This phenomenon is particularly relevant to spinally administered mu-opioid receptor agonists, which induce segmental analgesia often combined with segmental pruritus. The peripheral and central sensitization to pain and to itch exhibits striking similarities. Classical inflammatory mediators such as bradykinin have been shown to sensitize nociceptors for both itch and pain. Also regulation of gene expression induced by trophic factors, such as NGF, plays a major role in persistently increased neuronal sensitivity for itch and pain. Finally, itch and pain exhibit corresponding patterns of central sensitization. The knowledge of antagonistic interaction, but also of similar sensitization processes has major implication for antipruritic therapeutic approaches.

Atopy Patch Test – Reproducibility and Elicitation of Itch in Different Application Sites

We evaluated the reproducibility of atopy patch test reactions and the quality and quantity of itch in 16 patients with atopic eczema and a history of a positive atopy patch test reaction, comparing three different application sites. The allergen was re-applied simultaneously on both forearms and the back. Intensity and quality of pruritus were evaluated using a visual analogue scale and the Eppendorf itch questionnaire, respectively. The atopy patch test reaction was highly reproducible, occurring in 15/16 (94%) patients. Pruritus was reported by 14/16 (88%) patients. There was no significant difference in either the intensity or quality of itch between the two forearms and the back (p>0.05). The mean peak visual analogue scale itch score was comparable across all three test sites (range 28.3-31.9). Regarding quantification of test reactions, a positive reaction was more frequent on the back (94% versus 69% on the arms) and the peak atopy patch test score was higher on the back compared with the arms (right forearm, p=0.0018 and left forearm, p=0.0683). Allergens should preferably be applied on the back for the atopy patch test. However, the atopy patch test can induce atopic itch irrespective of the application site.

Itch: More than Skin Deep

Recent research in neurophysiology of itch has indicated the existence of itch-dedicated nociceptor neurones. The perception of itch is regulated by tonically inhibitory descending neuronal pathways and nociceptor spinal neuronal circuits. There is at present no convincing evidence of an 'itch centre' in the brain. A classification of itch has been proposed, based on neurophysiological considerations, which stresses the importance of neurogenic and neuropathic itch, and assists in differential diagnosis and selection of treatment. However, more than one class of itch can occur concurrently in the same patient. The importance of cross- talk between dermal mast cells and nociceptor nerve terminals, involving cleavage of proteinase-activated receptor 2 by mast cell tryptase, is highlighted. The pruritus of cholestasis is mediated at least in part by opioid peptides synthesized by the liver, and elevated levels of these mediators are found in the plasma and skin of patients with itch due to cholestasis. The combined use of both mu-receptor antagonists and kappa-receptor agonists (anti-pruritic) is worth exploring.

Pruritus in adult dermatomyositis

Dermatomyositis has a significant clinical component of pruritus that has not yet been studied. Pruritus can significantly affect the life of patients. The aim of the present work was to study the degree of pruritus experienced by patients. A four-question survey was sent to patients with documented dermatomyositis. The survey used a 100-mm Visual Analogue Scale (VAS) to describe current, worst and daily pruritus, and the effect this has on daily activities. Twenty-six subjects returned completed questionnaires: four had no pruritus; the majority had a significant amount with means above 50 on the VAS. A mean of 44.6 was found for the effect on daily life. Further studies should be performed to examine the prevalence and severity of pruritus in this population and it's effect on their quality of life. Clinicians must be aware of the significant pruritus and provide adequate therapy to improve quality of life.

Itch

Itch is a common skin sensation, with substantial effects on behaviour. Neurophysiological research has permitted accurate definition of neural pathways of itch, and has confirmed the distinctiveness of itch pathways in comparison with pain. A clinical classification of itch, based on such improved understanding, describes the difference between peripheral (pruritoceptive) and central (neurogenic or neuropathic) itch. New specific and sensitive investigational methods in people and animals enable us to better understand this bothersome symptom, and have important clinical implications. We describe the clinical classification of itch, new findings on neuropathophysiology of itch, methods for assessment, and improved treatments.