Somatosensory profiles in acute herpes zoster and predictors of postherpetic neuralgia

8. Herpes zoster and post herpetic neuralgia

INTRODUCTION

Patients suffering from postherpetic neuralgia (PHN) report unilateral chronic pain in one or more dermatomes after an acute herpes zoster (HZ) infection. The incidence of acute HZ ranges between three and five patients per 1000 person-years. In one out of four patients, acute HZ-related pain will transition into PHN. PHN can be very disabling for patients and reduce quality of life. Additionally, the treatment of PHN is characterized by high failure rates. The aim of this review is to give an update on the previous practical guideline published in 2011 and revised in 2015 (published in 2019) and to provide an overview of current interventional treatment options for HZ infection and PHN.

METHODS

The literature on the diagnosis and treatment of HZ and PHN was systematically reviewed and summarized.

RESULTS

The most important treatment for acute HZ-related pain is antiviral therapy within 72 h of symptom onset. Additional symptomatic treatment options are analgesic drugs according to the WHO pain ladder, tricyclic antidepressants (eg, nortriptyline), and antiepileptic drugs (eg, gabapentin). If pain is not sufficiently reduced, interventional treatment such as an epidural injection with local anesthetics and corticosteroids or pulsed radiofrequency of the dorsal root ganglion (DRG) are options. Treatment for PHN is preferably transdermal capsaicin, lidocaine, or oral drugs such as antidepressants or antiepileptics.

CONCLUSIONS

Treatment of acute HZ-related pain especially PHN is challenging. Besides the conventional treatment for PHN, interventional management is considered a new treatment option. PRF of DRG seems to be the most promising interventional management.

Predictive Value of Current Perception Threshold for Prognosis of Pulsed Radiofrequency in Patients with Acute Herpetic Neuralgia

Objective

This study aimed to evaluate the prognostic accuracy of the Current Perception Threshold (CPT) in Acute Herpetic Neuralgia (AHN) patients receiving Pulsed Radiofrequency (PRF) therapy and to develop a corresponding prognostic model.

Methods

We retrospectively analyzed data from 106 AHN patients treated with PRF between January 2022 and May 2023. The occurrence of Postherpetic Neuralgia (PHN) after treatment categorized patients into non-PHN and PHN groups. The predictive role of CPT indices for PRF outcomes was assessed using the Receiver Operating Characteristic (ROC) curve and Area Under Curve (AUC). Then the dataset was split into a training set (n=74) and a validation set (n=32). Factors associated with PHN development were identified using univariate and multivariate logistic regression. A nomogram model was developed using significant predictors and internal validation was performed using valid set data.

Results

Among the 106 patients, 45 had a poor prognosis. Significant differences in age, preoperative Numerical Rating Scale (NRS) score, and 5Hz CPT ratio were observed between the groups (p<0.05). Logistic regression identified these factors as independent predictors for PRF prognosis (p<0.05). The 5Hz CPT ratio demonstrated predictive value (AUC= 0.764, 95% CI: 0.674-0.855). The nomogram model, incorporating these predictors, showed high AUC in both the training (0.863, 95% CI: 0.776-0.950) and validation sets (0.859, 95% CI: 0.721-0.998). Calibration curves indicated good model fit, and the Hosmer-Lemeshow test confirmed this (p>0.05). Decision Curve Analysis (DCA) highlighted the model's predictive advantage.

Conclusion

The 5Hz CPT ratio can predict the prognosis of PRF in AHN patients. The nomogram model has high precision and clinical utility. It can help identify AHN patients with a poor PRF prognosis at an early stage and assist in clinical decision-making.

Identifying and Evaluating Biological Markers of Postherpetic Neuralgia: A Comprehensive Review

Postherpetic neuralgia (PHN) manifests as persistent chronic pain that emerges after a herpes zoster outbreak and greatly diminishes quality of life. Unfortunately, its treatment efficacy has remained elusive, with many therapeutic efforts yielding less than satisfactory results. The research to discern risk factors predicting the onset, trajectory, and prognosis of PHN has been extensive. However, these risk factors often present as nonspecific and diverse, indicating the need for more reliable, measurable, and objective detection methods. The exploration of potential biological markers, including hematological indices, pathological insights, and supportive tests, is increasing. This review highlights potential biomarkers that are instrumental for the diagnosis, management, and prognosis of PHN while also delving deeper into its genesis. Drawing from prior research, aspects such as immune responsiveness, neuronal injury, genetic makeup, cellular metabolism, and pain signal modulation have emerged as prospective biomarkers. The immune spectrum spans various cell subtypes, with an emphasis on T cells, interferons, interleukins, and other related cytokines. Studies on nerve injury are directed toward pain-related proteins and the density and health of epidermal nerve fibers. On the genetic and metabolic fronts, the focus lies in the detection of predisposition genes, atypical protein manifestations, and energy-processing dynamics, with a keen interest in vitamin metabolism. Tools such as functional magnetic resonance imaging, electromyography, and infrared imaging have come to the forefront in the pain signaling domain. This review compiles the evidence, potential clinical implications, and challenges associated with these promising biomarkers, paving the way for innovative strategies for predicting, diagnosing, and addressing PHN.

Characterization of the neuropathic pain component contributing to myalgia in patients with myotonic dystrophy type 1 and 2

Introduction

Chronic muscle pain is common in myotonic dystrophies (DM). Little is known about its pathophysiology. We aimed to investigate the characteristics of the neuropathic pain component contributing contributes to the pathogenesis of chronic pain in DM.

Methods

Twenty-one DM1 and 32 DM2 patients completed pain questionnaires (Brief pain inventory-BPI, PAIN-DETECT, pain disability index-PDI) and underwent neurological examination, nerve conduction studies (NCS), quantitative sensory testing (QST, dorsum of the right hand and right thigh) and skin biopsy to determine the intraepidermal nerve fiber density (IENFD, distal and proximal site of lower extremity). NCS and QST results at the thigh were compared to 27 healthy controls and IENFD and QST at the dorsum of the hand to published reference values.

Results

The sensory profile of DM2 patients was characterized by a loss in thermal and mechanical detection, while DM1 patients showed reduced mechanical and heat pain thresholds and higher mechanical pain sensitivity. Both DM groups showed pressure hyperalgesia. IENFD was reduced in 63% of DM1 patients and 50% of DM2. The slightly higher pain interference and disability found in DM2 was rather due to age difference than disease.

Conclusion

Similar pain mechanisms likely occur in both DM1 and DM2, even though a tendency toward more pain sensitivity was observed in DM1 and more sensory loss in DM2. Both QST and reduced IENFD highlight the presence of peripheral nerve damage in DM. This must be considered for the best pain management strategies.

HSV-1 reactivation results in post-herpetic neuralgia by upregulating Prmt6 and inhibiting cGAS-STING

Chronic varicella zoster virus (VZV) infection induced neuroinflammatory condition is the critical pathology of post-herpetic neuralgia (PHN). The immune escape mechanism of VZV remains elusive. As to mice have no VZV infection receptor, herpes simplex virus type 1 (HSV-1) infection is a well established PHN mice model. Transcriptional expression analysis identified that the protein arginine methyltransferases 6 (Prmt6) was upregulated upon HSV-1 infection, which was further confirmed by immunofluorescence staining in spinal dorsal horn. Prmt6 deficiency decreased HSV-1-induced neuroinflammation and PHN by enhancing antiviral innate immunity and decreasing HSV-1 load in vivo and in vitro. Overexpression of Prmt6 in microglia dampened antiviral innate immunity and increased HSV-1 load. Mechanistically, Prmt6 methylated and inactivated STING, resulting in reduced phosphorylation of TANK binding kinase-1 (TBK1) and interferon regulatory factor 3 (IRF3), diminished production of type I interferon (IFN-I) and antiviral innate immunity. Furthermore, intrathecal or intraperitoneal administration of the Prmt6 inhibitor EPZ020411 decreased HSV-1-induced neuroinflammation and PHN by enhancing antiviral innate immunity and decreasing HSV-1 load. Our findings revealed that HSV-1 escapes antiviral innate immunity and results in PHN by upregulating Prmt6 expression and inhibiting the cGAS-STING pathway, providing novel insights and a potential therapeutic target for PHN.

Genetics of causal relationships between circulating inflammatory proteins and postherpetic neuralgia: a bidirectional Mendelian randomization study

Objective

According to data from several observational studies, there is a strong association between circulating inflammatory cytokines and postherpetic neuralgia (PHN), but it is not clear whether this association is causal or confounding; therefore, the main aim of the present study was to analyze whether circulating inflammatory proteins have a bidirectional relationship with PHN at the genetic inheritance level using a Mendelian randomization (MR) study.

Methods

The Genome-Wide Association Study (GWAS) database was used for our analysis. We gathered data on inflammation-related genetic variation from three GWASs of human cytokines. These proteins included 91 circulating inflammatory proteins, tumor necrosis factor-alpha (TNF-α), macrophage inflammatory protein 1b (MIP-1b), and CXC chemokine 13 (CXCL13). The PHN dataset was obtained from the FinnGen biobank analysis round 5, and consisted of 1,413 cases and 275,212 controls. We conducted a two-sample bidirectional MR study using the TwoSampleMR and MRPRESSO R packages (version R.4.3.1). Our main analytical method was inverse variance weighting (IVW), and we performed sensitivity analyses to assess heterogeneity and pleiotropy, as well as the potential influence of individual SNPs, to validate our findings.

Results

According to our forward analysis, five circulating inflammatory proteins were causally associated with the development of PHN: interleukin (IL)-18 was positively associated with PHN, and IL-13, fibroblast growth factor 19 (FGF-19), MIP-1b, and stem cell growth factor (SCF) showed reverse causality with PHN. Conversely, we found that PHN was closely associated with 12 inflammatory cytokines, but no significant correlation was found among the other inflammatory factors. Among them, only IL-18 had a bidirectional causal relationship with PHN.

Conclusion

Our research advances the current understanding of the role of certain inflammatory biomarker pathways in the development of PHN. Additional verification is required to evaluate the viability of these proteins as targeted inflammatory factors for PHN-based treatments.

Pain in the Context of Sensory Deafferentation

Pain that accompanies deafferentation is one of the most mysterious and misunderstood medical conditions. Prevalence rates for the assorted conditions vary considerably but the most reliable estimates are greater than 50% for strokes involving the somatosensory system, brachial plexus avulsions, spinal cord injury, and limb amputation, with controversy surrounding the mechanistic contributions of deafferentation to ensuing neuropathic pain syndromes. Deafferentation pain has also been described for loss of other body parts (e.g., eyes and breasts) and may contribute to between 10% and upwards of 30% of neuropathic symptoms in peripheral neuropathies. There is no pathognomonic test or sign to identify deafferentation pain, and part of the controversy surrounding it stems from the prodigious challenges in differentiating cause and effect. For example, it is unknown whether cortical reorganization causes pain or is a byproduct of pathoanatomical changes accompanying injury, including pain. Similarly, ascertaining whether deafferentation contributes to neuropathic pain, or whether concomitant injury to nerve fibers transmitting pain and touch sensation leads to a deafferentation-like phenotype can be clinically difficult, although a detailed neurologic examination, functional imaging, and psychophysical tests may provide clues. Due in part to the concurrent morbidities, the physical, psychologic, and by extension socioeconomic costs of disorders associated with deafferentation are higher than for other chronic pain conditions. Treatment is symptom-based, with evidence supporting first-line antineuropathic medications such as gabapentinoids and antidepressants. Studies examining noninvasive neuromodulation and virtual reality have yielded mixed results.

Comprehensive quantitative sensory testing shows altered sensory function in women with chronic pelvic pain: results from the Translational Research in Pelvic Pain (TRiPP) Study

ABSTRACT

Chronic pelvic pain (CPP), despite its high prevalence, is still relatively poorly understood mechanistically. This study, as part of the Translational Research in Pelvic Pain (TRiPP) project, has used a full quantitative sensory testing (QST) paradigm to profile n = 85 women with and without CPP (endometriosis or bladder pain specifically). We used the foot as a control site and abdomen as the test site. Across 5 diagnostically determined subgroups, we found features which are common across different aetiologies, eg, gain of function in pressure pain threshold (PPT) when assessing responses from the lower abdomen or pelvis (referred pain site). However, disease-specific phenotypes were also identified, eg, greater mechanical allodynia in endometriosis, despite there being large heterogeneities within diagnostic groups. The most common QST sensory phenotype was mechanical hyperalgesia (>50% across all the groups). A "healthy' sensory phenotype was seen in <7% of CPP participants. Specific QST measures correlated with sensory symptoms assessed by the painDETECT questionnaire (pressure-evoked pain [painDETECT] and PPT [QST] [ r = 0.47, P < 0.001]; mechanical hyperalgesia (painDETECT) and mechanical pain sensitivity [MPS from QST] [ r = 0.38, P = 0.009]). The data suggest that participants with CPP are sensitive to both deep tissue and cutaneous inputs, suggesting that central mechanisms may be important in this cohort. We also see phenotypes such as thermal hyperalgesia, which may be the result of peripheral mechanisms, such as irritable nociceptors. This highlights the importance of stratifying patients into clinically meaningful phenotypes, which may have implications for the development of better therapeutic strategies for CPP.

Analysis of the Risk Factors for Mechanical Allodynia in Herpetic Neuralgia: A Retrospective Cross-Sectional Study

Purpose

Mechanical allodynia is reportedly common during herpetic neuralgia. The purpose of this study was to establish a risk prediction model to predict the individual risk of allodynia in herpetic neuralgia.

Methods

Three hundred and eighty-six patients with trunk herpetic neuralgia were divided into two regions, T2-5 and T6-11. The causality between allodynia and other factors was analyzed by a binary logistic regression model.

Results

42.2% of subjects had allodynia, 137 suffered from dynamic allodynia, and 110 with dynamic allodynia experienced local sweating. The following 5 items as predictors determined this model: local sweating (Odd Ratio = 27.57, P<0.001), lesion location (Odd Ratio=2.46, P =0.017), pain intensity (Odd Ratio=1.38, P =0.020), pain duration (Odd Ratio=0.94, P =0.006), and local scars (Odd Ratio=0.07, P<0.001). The presence and development of allodynia are associated with local sweating. The positive proportion of the Iodine-starch test between the T2-5 (50.0%) with the T6-11 (23.7%) had a statistically significant difference (χ2=5.36, P=0.021). 29.5% of patients at the T2-6 had obvious sweating, which was different from only sticky feelings at the T6-11 (70.5%, χ2=10.88, P=0.001). 19.2% of patients with residual scars and allodynia was significantly lower than 48.5% of patients without allodynia (χ2=15.28, P<0.001).

Conclusion

This analysis suggests that local sweating is a concomitant symptom in dynamic allodynia, which imply the sympathetic nerves innervating the sweat glands of the skin were also involved during herpetic neuralgia. This may assist in the evaluation of dynamic allodynia and prove the role of sympathetic nerve intervention for herpetic neuralgia.

Evaluation of the correlation of dorsal root ganglia and spinal nerves with clinical symptoms in patients with postherpetic neuralgia using magnetic resonance neurography

Purpose

To assess changes of dorsal root ganglia (DRG) and spinal nerves in patients with postherpetic neuralgia (PHN), and investigate the correlation between DRG morphology and clinical symptoms in PHN patients using magnetic resonance neurography (MRN).

Methods

In this case-control study, forty-nine lesioned DRG in 30 patients and 49 normal DRG in 30 well-matched (age, sex, height, weight) healthy controls were assessed. Clinical symptoms of patients (pain, allodynia, itching, and numbness) were assessed. MRN features (DRG volume (VDRG), the largest diameter (Dmax) of spinal nerves, signal intensity of DRG and spinal nerves (M-value)) were measured in all participants. Multilinear regression analysis was used to evaluate the relationship between the DRG morphology and clinical symptoms in patients.

Results

The volume and relative M-value of lesioned DRG in patients were significantly higher than those on the same side of healthy controls (p = 0.013, p < 0.001, respectively). The mean Dmax and relative M-value of spinal nerves on the lesioned side were significantly higher than those on the contralateral and same side of healthy controls (p < 0.0001, p = 0.0001, p = 0.0011, p = 0.0053, respectively). No difference was found between the mean VDRG of the lesioned and contralateral sides. Multiple linear regression analysis revealed that disease duration was independent risk factor for the maximum rate of VDRG differences (p = 0.013).

Conclusions

DRG and spinal nerves on the lesioned side are swollen during PHN. Disease duration is an independent risk factor for morphological differences in the lesioned DRG of PHN patients. This study provides important guidance for individualized treatments of PHN.

Top 100 Most-Cited Papers in Herpes Zoster from 2000 to 2022: A Bibliometric Study

Background

In recent years, the incidence of herpes zoster has risen steeply, the exact pathogenesis of the acute pain and the transformation into postherpetic neuralgia are still obscure, and the absence of effective management remains a major therapeutic challenge. The purpose of this study was to perform a qualitative and quantitative bibliometric analysis of the 100 most cited papers on herpes zoster.

Materials and methods

Related literature were retrieved from the Web of Science Core Collection. Excel and VOSviewer software were applied to quantitatively analyze, and construct the bibliometric network charts.

Results

The Top 100 most-cited papers published between 2000 and 2018 showed a fluctuating downward trend. The most studies were published in the year of 2000 (n = 12). The article entitled "A vaccine to prevent herpes zoster and postherpetic neuralgia in older adults" from Oxman MN, was the most-cited publication. The United States was the most contributing country, followed by the United Kingdom, and Italy. Finland occupied the highest citations per publication (CPP). The University of Colorado topped the list of institutions with the most publications with 18 articles and also had the most citations (average citations: 281.78 per article). Myron J Levin from the University of Colorado School of Medicine is the most published and most cited researcher overall, whereas Duke University's John W Gnann tops the list in terms of average CPP.

Conclusion

In terms of the quantity of T100 articles, researchers, and organizations, the US is the predominant country. The most T100 papers were published in the special journal Clinical Infectious Diseases. The most academic focus remain the remedies for postherpetic neuralgia and vaccine development for individualized groups.

Investigating the Therapeutic Effect of Intradermal Acupuncture for Acute Herpes Zoster and Assessing the Feasibility of Infrared Thermography for Early Prediction of Postherpetic Neuralgia: Study Protocol for a Randomized, Sham-Controlled, Clinical Trial

INTRODUCTION

Herpes zoster (HZ) can adversely influence patients' quality of life and sometimes it can develop postherpetic neuralgia (PHN). To date, it remains challenging to be managed by currently available therapies. Intradermal acupuncture (IDA) has the potential to be an adjunctive therapy for acute HZ and infrared thermography (IRT) may be useful for predicting PHN; however, current evidence remains inconclusive. Therefore, the purposes of this trial are to 1) evaluate the efficacy and safety of IDA as an adjunctive therapy for acute HZ; 2) to explore the feasibility of IRT for early prediction of PHN and as an objective tool to aid in subjective pain assessment in acute HZ.

METHODS

This study is designed as a randomized, parallel-group, sham-controlled, and patient-assessor-blinded trial, including 1-month treatment and 3-month follow-ups. Seventy-two qualified participants will be randomly split into the IDA or sham IDA group in a ratio of 1:1. Apart from standard pharmacological treatments in both groups, the two groups will receive 10 sessions of IDA or sham IDA, respectively. Primary outcome measures are the visual analog scale (VAS), indicators of herpes lesions' recovery, the temperature of the pain area, and the incidence rate of PHN. The secondary outcome is the 36-item Short Form Health Survey (SF-36). Indicators of herpes lesions' recovery will be assessed at each visit and follow-ups. The remaining outcomes will be assessed at baseline, 1 month after intervention, and 3-month follow-up. Safety evaluation will be determined by adverse events during the trial.

CONCLUSION

Expected results will determine whether IDA can enhance therapeutic effectiveness of pharmacotherapy for acute HZ with acceptable safety profile. In addition, it will verify the accuracy of IRT for early prediction of PHN and as an objective tool of subjective pain for acute HZ.

TRIAL REGISTRATION

Clinicaltrials.gov (identification number: NCT05348382; Registered 27 April 2022, https://clinicaltrials.gov/ct2/show/NCT05348382).

Pain Fluctuations of Women with Subacute Herpetic Neuralgia During Local Methylcobalamin in Combination with Lidocaine Treatment: A Single-Blinded Randomized Controlled Trial

Purpose

To evaluate the efficacy and pain fluctuations of methylcobalamin in combination with lidocaine local injection treatment for subacute herpetic neuralgia (SHN).

Methods

Seventy-nine women (60.4 ± 2.7 years) with thoracic SHN were enrolled and randomized to receive a combination of methylcobalamin and lidocaine local injection (MI, N=40), or a combination of lidocaine patch 5% and oral methylcobalamin (PO, N=39) for four weeks. Repeated-measures analyses of variance were used to evaluate the effect on pain levels. Generalized estimation equations were used to analyze the cause-effect relationship between pain fluctuations and influencing factors.

Results

At the treatment endpoint, the group, treatment time, and group interacted with treatment time effects of the pain scores and area were statistically significant (P<0.001), The pain scores were 2.9 ±0.9 (MI) and 4.3 ± 1.5 (PO). 80.00% (MI) or 28.21% (PO) of patients had pain scores ≤ 3, the odds ratio was 2.84 (95% CI: 1.68 to 4.79). The incidence of postherpetic neuralgia was 5.0% (2/40) at 3 months. Pain fluctuated repeatedly during treatment. The pain fluctuation increased from 8.75 log folds in the afternoon, to 79.85 log folds at night. With the ADLs level increasing from 1 to 3, the pain fluctuated from 4.28 to 17.70 log folds. Allodynia, itching, sleep quality, and ADLs were the significant influencing factors (P<0.05).

Conclusion

This study validated the efficacy of methylcobalamin combined with lidocaine for SHN, and confirmed that pain levels in patients with SHN had an obvious circadian rhythm. ADLs were an important cause of pain fluctuations.

RNA-seq analysis revealed genes associated with neuropathic pain induced by chronic compressive injury in interferon regulatory factors 4 knockout mice

OBJECTIVE

To explore the differential expression of genes between wild-type chronic compressive injury (CCI) mice (WT-CCI) and interferon regulatory factors 4 (IRF4) knockout CCI mice (KO-CCI) by RNA-seq analysis of the mouse spinal cord.

METHODS

RNA-seq analysis of the spinal cord tissue of the chronic sciatic nerve ligation mice and Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses were used.

RESULTS

A total of 104 genes were up-regulated and 116 genes were down-regulated in spinal cord of the mice in IRF4 knockout (KO-CCI) group compared with that in the wild-type CCI (WT-CCI) group. There were 1472 differentially expressed genes in the biological process group, 62 differentially expressed genes in the cellular component group, and 163 differentially expressed genes in the molecular function group in KO-CCI mice. A total of 14 genes related to inflammatory reactions were differentially expressed. Real-time PCR results confirmed that Pparg and Grpr mRNA expression was up-regulated and Arg 1 and Ccl11 mRNA expression was down-regulated in the KO-CCI group.

CONCLUSION

IRF4 is involved in neuropathic pain in CCI mice, IRF4 may participate in neuropathic pain by regulating Grpr, Mas1, Galr3, Nos2, Arg1, Ccl11, Ptgs2, S100a8, Pparg, Cd40, Has2, Gpr151, Il123a, Capns2, Ankrd1, Ccnb1, and Nppb genes.

Similarities in the Neuropathy Phenotype of Cancer Survivors Who Received Different Classes of Chemotherapy Drugs

With the advent of platinum and taxane compounds used as single agents or in combination regimens, survival rates for some of the most common cancers have improved substantially. However, information on differences in the chemotherapy-induced peripheral neuropathy (CIPN) phenotype among single and combination regimens is limited. Study's purposes were to evaluate for differences in demographic and clinical characteristics; subjective and objective measures of CIPN; as well as the severity of common symptoms and quality of life among survivors who received platinum- (n = 95), taxane- (n = 200), or platinum and taxane-containing (n = 131) regimens. Patients completed self-report questionnaires (ie, duration of CIPN, pain intensity, pain qualities, pain interference) and underwent a physical examination that evaluated light touch, pain, and cold sensations and balance. For most of the subjective and objective measures of CIPN, as well as symptom severity and quality of life scores, no differences were found among the 3 chemotherapy groups. In all 3 chemotherapy treatment groups, CIPN was a painful, small fiber, and length dependent neuropathy. These findings support the hypothesis that CIPN induced by different classes of chemotherapy, as single agents or in combination, produce a similar CIPN phenotype which raises the possibility that CIPN induced by diverse chemotherapy protocols has the same underlying mechanism. PERSPECTIVE: In this study, that compared patients who received only platinum, only taxane, or both platinum and taxane containing regimens, no differences were found among the 3 groups in the CIPN phenotype. Findings raise the possibility that CIPN induced by diverse chemotherapy protocols has the same underlying mechanism.

Risk Factors for Poor Pain Control in Zoster-Associated Pain: A Retrospective Study

INTRODUCTION

The objective was to investigate the risk factors for poor pain control in patients with herpes zoster (HZ)-associated neuropathic pain treated with drugs combined with nerve block therapy. Neuropathic pain commonly follows HZ. Nerve block therapy is the most commonly used clinical treatment for such pain, combining anti-inflammation and analgesia to prevent peripheral sensitization of nerve.

METHODS

Using clinical practice data from a cohort study at our research center, we established a multivariate logistic regression model to investigate potential risk factors for poor control of zoster-associated pain (ZAP) treated with drugs plus nerve block therapy, including demographic characteristics, complications, laboratory tests, and characteristics of HZ attacks.

RESULTS

Of the 429 patients with ZAP who received drugs plus nerve block therapy, 95 (22.14%) had poor pain control after treatment. The risk of poor pain control was closely related to presence of cancer (odds ratio (OR) 4.173, 95% confidence interval (CI) 1.342-12.970), numerical rating scale score on admission (OR 1.929, 95% CI 1.528-2.434), and red blood cell count (OR 0.560, 95% CI 0.328-0.954). Area under the receiver operator characteristic curve was 0.730. Goodness of fit (Hosmer-Lemeshow) was 0.874.

CONCLUSIONS

The risk of poor pain control in patients with ZAP increased as a result of certain patient characteristics and complications, especially severe pain before treatment and cancer.

Patient-reported quality of life in patients suffering from acute herpes zoster-a systematic review with meta-analysis

Objectives

Herpes Zoster (HZ) is a common painful, debilitating condition caused by reactivation of the varicella-zoster virus. It is characterized by a painful skin eruption which is very complex to treat. Studies have reported that HZ negatively affects Quality of Life (QoL), but no large systematic review on this topic has been published to date. This systematic review aims to summarize the current data on patient-reported QoL amongst patients diagnosed with HZ.

Methods

We searched Medline, Embase, Cochrane Library, CINAHL, and PsycINFO. The primary outcome was the change in percent impairment of QoL compared to normative data. Secondary outcomes were meta-analyses comparing reported QoL to a control group or normative data.

Results

We assessed a total of 536 studies for inclusion. Thirteen studies were included in the systematic review and five studies in the meta-analyses. The total number of patients was 5472.

Conclusions

This systematic review and meta-analysis found lower reported QoL amongst patients diagnosed with acute herpes zoster compared to normative values. Our data show that acute herpes zoster significantly reduces the quality of life of the patients affected.

Fire Needling Acupuncture for Adult Patients with Acute Herpes Zoster: Protocol of a Systematic Review and Meta-Analysis

Background

Acute herpes zoster (HZ) is characterized as a vesicular rash with unilateral distribution produced by the reactivation of varicella zoster virus. It can induce various comorbidities that can adversely influence the quality of life of patients. The purpose of this systematic review is to assess the effect and safety of fire needling acupuncture on acute HZ.

Methods

Three English databases (PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials) and four Chinese Databases (China National Knowledge Infrastructure, Wanfang database, Chongqing VIP database, and China Biology Medicine database) will be searched from their inceptions to July 2022. Randomized controlled trials investigating fire needling acupuncture therapy for acute HZ will be included, regardless of publication status. Two reviewers will independently conduct the study screening, data extraction, and research quality assessments. The primary outcome measures are the Pain Visual Analogue Scale and the occurrence of postherpetic neuralgia. Secondary outcomes measures are the evaluation of skin lesions, time to resolution of pain, tolerance evaluation, total effective rate, adverse events and changes in inflammatory and immune suppression markers in peripheral plasma. All included studies will be assessed for methodological quality via the Cochrane Collaboration’s bias risk assessment tool. Meta-analyses will be undertaken using Review Manager V.5.3 software. The findings will be reported as the risk ratio of the binary data and the mean difference (MD) or standardized MD of the continuous data. Subgroup analyses and sensitivity analyses will be conducted where appropriate. The Grading of Recommendations Assessment, Development, and Evaluation will be used to assess evidence certainty.

Results

From the study, we will ascertain the effects and safety of fire needling acupuncture on acute HZ.

Conclusion

This study will validate the effects and safety of fire needling acupuncture in the management of acute HZ, generating new evidence to guide acupuncture interventions for acute HZ in the future.

Registration Number

PROSPERO CRD42020199047.

When cooling of the skin is perceived as warmth: Enhanced paradoxical heat sensation by pre-cooling of the skin in healthy individuals

A paradoxical heat sensation (PHS) is the misperception of warmth when the skin is cooled. PHS is uncommon in healthy individuals but common in patients with neuropathy and is associated with reduced thermal sensitivity. Identifying conditions that contribute to PHS may indirectly help us understand why some patients experience PHS. We hypothesized that pre-warming increased the number of PHS and that pre-cooling had minimal effect on PHS. We tested 100 healthy participants' thermal sensitivity on the dorsum of their feet by measuring detection and pain thresholds to cold and warm stimuli and PHS. PHS was measured using the thermal sensory limen (TSL) procedure from the quantitative sensory testing protocol of the German Research Network on Neuropathic Pain and by using a modified TSL protocol (mTSL). In the mTSL we examined the participants' thermal detection and PHS after pre-warming of 38°C and 44°C and pre-cooling of 26°C and 20°C. Compared to a baseline condition, the number of PHS responders was significantly increased after pre-cooling (20°C: RR = 1.9 (1.1; 3.3), p = 0.023 and 26°C: RR = 1.9 (1.2; 3.2), p = 0.017), but not significantly after pre-warming (38°C: RR = 1.5 (0.86; 2.8), p = 0.21 and 44°C: RR = 1.7 (.995; 2.9), p = 0.078). Pre-warming and pre-cooling increased the detection threshold of both cold and warm temperatures. We discussed these findings in relation to thermal sensory mechanisms and possible PHS mechanisms. In conclusion, PHS and thermosensation are closely related and pre-cooling can induce PHS responses in healthy individuals.

Efficacy of Internal Heat Acupuncture Combined with High-Voltage Long-Duration Pulsed Radiofrequency on Subacute Postherpetic Neuralgia: A Retrospective Study

Objectives

This study aims at investigating the internal heat acupuncture (IHA) combined with the high-voltage long-duration pulsed radiofrequency (PRF) therapeutic effect on subacute postherpetic neuralgia (PHN).

Methods

This retrospective study comprised 81 cases with PHN. They were divided into three groups: IHA combined with the high-voltage long-duration PRF group (IHA-PRF), intradermal injection combined with the high-voltage long-duration PRF group (II-PRF), and the high-voltage long-duration PRF group. The pain numerical rating score (NRS), IL-6, Gal-3, and blood glucose levels were recorded before and after treatment.

Results

Compared with before treatment, NRS scores of the three groups were all decreased at each time point. NRS scores of the IHA-PRF group patients decreased significantly in comparison to the PRF group at 1, 4, 8, and 12 weeks following treatment, while group II-PRF only decreased significantly at one week following treatment. Compared with groups II-PRF and PRF, respectively, IL-6 and Gal-3 levels in plasma of patients in group IHA-PRF were significantly decreased at 4 and 12 weeks after treatment. The effective rate of group IHA-PRF was 88.9%, which was considerably more than the other groups, II-PRF (63.0%) and PRF (63.0%). Compared with group II-PRF, patients' blood glucose levels in IHA-PRF and PRF groups significantly decreased three days and one week after treatment.

Conclusion

Internal heat acupuncture combined with high-voltage long-duration pulsed radiofrequency has a satisfactory therapeutic effect on subacute PHN and has no obvious adverse reactions, which is especially suitable for patients with poor blood glucose control.

Research Trends and Hotspots on Herpes Zoster: A 10-Year Bibliometric Analysis (2012-2021)

Purpose

Herpes zoster infection, with its considerable burden to individuals and society, remains a challenge around the world. However, to the knowledge of the authors, little bibliometric quantitative or qualitative analysis has been carried out to evaluate herpes zoster research. This study aimed to use a bibliometric analysis to evaluate current publication trends and hotspots on herpes zoster research worldwide, in order to advance research in this field.

Methods

Relevant publications from January 2012 to December 2021 were collected from the Web of Science Core Collection database. Citespace (V5.8.R3) was used to analyze the research points, including publication countries, institutions and authors, cited author, cited reference and their clustering, and keyword co-occurrence, and burst keyword to acquire research trends and hotspots.

Results

A total of 9,259 publications were obtained, with a steady increase in the number of annual publications during the decade. Articles were the main type of publication. The United States is the leading country in this research, and the University of Colorado has the highest influence in this field. Oxman is the most representative author, with a main research interest in herpes zoster vaccines. The top five cited authors' publications focused on herpes zoster vaccines, molecular mechanisms, and postherpetic neuralgia. A co-citation map resulted 19 main clusters, and revealed that vaccines, postherpetic neuralgia, treatments, varicella zoster virus and its mechanisms, and epidemiology of herpes zoster were the current research focus after clustering co-cited publications. Human herpesviruses, antiviral prophylaxis, rheumatoid arthritis, recombinant zoster vaccine, varicella vaccination and postherpetic neuralgia were the top clusters after co-occurrence keywords analysis. Moreover, burst keywords detection showed that the subunit vaccine was the new hotspot in the field of herpes zoster.

Conclusion

This bibliometric study defined the overall prospects in the field of herpes zoster and provided valuable instruction for the ongoing research. The keyword "subunit vaccine" indicated that a vaccine for herpes zoster prevention was the hotspot. Efforts to prevent varicella zoster virus infection will be essential to improve herpes zoster outcomes.

A Comparison Between Effects of Amenamevir and Famciclovir on Intensities of Acute Pain and the Incidence of Postherpetic Neuralgia in Adult Patients with Herpes Zoster

Objective

Herpes zoster (HZ) is a common disease, whose most common complication is postherpetic neuralgia (PHN). We conducted this study to compare effects of amenamevir (AMNV) and famciclovir (FCV) on intensities of acute HZ pain and the incidence of PHN, which have not been compared yet.

Methods

After approval by the Ethics Committee, we retrospectively investigated adult patients with HZ treated with AMNV or FCV at Juntendo University Hospital between October, 2018 and February, 2020. We compared, between 143 AMNV-treated and 131 FCV-treated patients, pain scores of acute HZ pain evaluated on an 11-point numerical rating scale (NRS) and the incidence of PHN with the Mann-Whitney U test and Pearson's chi-square test, respectively. The univariate logistic regression analysis was used to identify predictors of PHN.

Results

Pain scores during the acute HZ period remained significantly lower in AMNV-treated patients than FCV-treated patients (p = 0.049, 0.011, and 0.016 for Day 3-4, Day 7, and Week 2-3, respectively), although the pain score at Day 0 before treatment didn't differ between them (p > 0.05). The incidence of PHN didn't differ between them (9.8% vs. 11.5%, p > 0.05). In the total cohort, the pain score at Week 2-3 was significantly associated with the development of PHN (r 2 = 0.180, p < 0.00001).

Conclusions

Compared with FCV, AMNV was more effective in reducing acute HZ pain, possibly reflecting its unique mechanism of action. However, AMNV didn't reduce the incidence of PHN possibly due to the multifactorial etiology of PHN.

Safety and Efficacy of CT-Guided Pulsed Radiofrequency Combined with Steroid and Ozone Injection-Treated Cervical 3-8 Herpes Zoster Neuralgia Using a Posterior and Upper Quarter of the Cervical Foramina Puncture Approach

Background

Herpes zoster neuralgia has a considerable impact on people’s quality of life, especially after the development of postherpetic neuralgia. There are many clinical reports on the treatment of herpes zoster neuralgia, but there have been no special reports on the treatment of herpes zoster involving the neck. Our research focuses on a posterior and upper quarter of the cervical foramina puncture approach for herpes zoster involving the cervical 3–8 (C3-8) nerve region and to consider the safety and efficacy of pulsed radiofrequency combined with steroid injection and ozone injection in this puncture path under CT guidance.

Materials and Methods

A total of 104 patients with herpes zoster neuralgia involved in the cervical 3–8 nerve region use a posterior and upper quarter of the cervical foramina puncture approach received pulsed radiofrequency combined with steroid and ozone injection to the dorsal root ganglion. The total number of injection procedures, complications, NRS collection (preprocedure, postprocedure at once, two, four and 12 weeks) and drug dose decreases were documented.

Results

During a total of 257 procedures, 254 procedures successfully completed PRF (3 cases failed to reach the C8 aim points), and the rate of puncture failure was 1.17%. Drug injection was successfully performed in 252 procedures (the injection success rate was 99.21%); the NRSs (preprocedure, postprocedure at once, two, four and twelve weeks) were 5.75 ± 0.682, 2.6 ± 1.023, 2.21 ± 0.925, 1.89 ± 1.162, and 1.43 ± 1.369, and the difference among them was statistically significant. Drug dosages decreased before and after operation and showed statistically significant differences.

Conclusion

Pulsed radiofrequency combined with steroid and ozone injection for herpes zoster neuralgia involving the C3-8 nerves under CT guidance through a posterior superior quarter approach showed safety and efficacy and had a high success rate, and the NRS decreased significantly.

Efficacy of Electroacupuncture Therapy in Patients With Postherpetic Neuralgia: Study Protocol for a Multicentre, Randomized, Controlled, Assessor-Blinded Trial

Introduction: The efficacy of conventional treatments for treating postherpetic neuralgia (PHN) remains unsatisfactory. Thus, this multicentre, randomized controlled, assessor-blinded trial aims to investigate the efficacy and safety of electroacupuncture (EA) therapy in patients with PHN. Methods and Analysis: This multicentre randomized controlled trial will enroll 132 patients with PHN from 3 hospitals. All patients will be randomly assigned to either the EA combined with medication group or medication group through a computerized central randomization system in a 1:1 ratio. Outcome measures will be assessed before intervention, at 2, 4, 6 weeks after intervention and at the end of 8-week follow-up. Primary outcomes will be sensory thresholds and pain intensity. Secondary outcomes will include dosage of analgetic, quality of life, anxiety, and depression severity and sleep quality. All adverse effects will be assessed during the trial. Conclusions: This study will provide evidence to ascertain whether EA is effective and safe for treating PHN. Ethics and Dissemination: Ethics approval (No.ZSLL-KY-2017-025) has been obtained from the Ethics Committee of The Third Affiliated Hospital of Zhejiang Chinese Medical University. Informed consent will be signed prior to subject enrolment. The results will be submitted to international peer-reviewed journals and presented at international conferences. Trial Registration Number: The study protocol has been registered in the clinicaltrials registry with the identification code NCT04594226.

AAAPT Diagnostic Criteria for Acute Neuropathic Pain

OBJECTIVE

Acute neuropathic pain is a significant diagnostic challenge, and it is closely related to our understanding of both acute pain and neuropathic pain. Diagnostic criteria for acute neuropathic pain should reflect our mechanistic understanding and provide a framework for research on and treatment of these complex pain conditions.

METHODS

The Analgesic, Anesthetic, and Addiction Clinical Trial Translations, Innovations, Opportunities, and Networks (ACTTION) public-private partnership with the U.S. Food and Drug Administration (FDA), the American Pain Society (APS), and the American Academy of Pain Medicine (AAPM) collaborated to develop the ACTTION-APS-AAPM Pain Taxonomy (AAAPT) for acute pain. A working group of experts in research and clinical management of neuropathic pain was convened. Group members used literature review and expert opinion to develop diagnostic criteria for acute neuropathic pain, as well as three specific examples of acute neuropathic pain conditions, using the five dimensions of the AAAPT classification of acute pain.

RESULTS

AAAPT diagnostic criteria for acute neuropathic pain are presented. Application of these criteria to three specific conditions (pain related to herpes zoster, chemotherapy, and limb amputation) illustrates the spectrum of acute neuropathic pain and highlights unique features of each condition.

CONCLUSIONS

The proposed AAAPT diagnostic criteria for acute neuropathic pain can be applied to various acute neuropathic pain conditions. Both the general and condition-specific criteria may guide future research, assessment, and management of acute neuropathic pain.

How Do Neurons Signal Itch?

Mechanistic theories of itch are based on neuronal specificity, stimulus intensity, and temporal or spatial discharge patterns. Traditionally, these theories are conceptualized as mutually exclusive, assuming that finding evidence for one theory would exclude the others and could sufficiently explain itch. Current experimental data primarily support the specificity or pattern theory of itch. However, in contrast to an assumed inherent exclusivity, recent results have shown that even within itch-specific pathways in the spinal cord, temporal discharge patterns are important as sustained pruriceptor is required to allow successful transsynaptic signal progression. Also, optogenetic activation of pruriceptors suggest that the combination of neuronal specificity and temporal pattern determines the sensory effect: tonic activation of pruriceptors is required to induce scratching behavior whereas short-lasting stimulation rather causes withdrawal. In addition to the mere duration of discharge, also the temporal pattern or spatial aspects could critically contribute to elicit pruritus instead of pain. Basic neurophysiological studies trying to validate neuronal theories for pruritus in their pure form provide unitary concepts leading from neuronal discharge to the itch sensation. However, the crucial clinical questions have the opposite perspective: which mechanisms explain the chronic itch in a given patient or a given disease? In trying to solve these clinical problems we should not feel bound to the mutual exclusive nature of itch theories, but rather appreciate blending several theories and also accept combinations of itch and pain. Thus, blended versions of itch theories might better suffice for an explanation of chronic itch in patients and will improve the basis for mechanistic treatment options.

Application and Therapeutic Effect of Puncturing of the Costal Transverse Process for Pulsed Radiofrequency Treated T1-T3 Herpes Zoster Neuralgia

Purpose

In CT-guided dorsal root ganglion puncture, especially T1–T3, it is often difficult to reach the target due to obstruction of the lamina, transverse process, and ribs. Therefore, a safe and effective puncture method with high success rate is urgently needed to guide us in our clinical work.

Patients and Methods

A total of 44 patients with dorsal root ganglion underwent pulsed radiofrequency therapy for pain T1–T3 herpes zoster neuralgia at the pain department of Affiliated Hospital of Jiaxing University from January 2019 to February 2020 were retrospectively reviewed. Each patient underwent the same surgical method. The patient’s operation time, CT filming times, nerve electrophysiological tests, the NRS scores before and after operation at one, four, eight, and 12 weeks, Pittsburgh Sleep Disorder Index (PSQI), dosage of gabapentin capsules and tramadol hydrochloride sustained-release tablets, surgical complications and incidence of postherpetic neuralgia (PHN) were recorded.

Results

The success rate of 44 patients who underwent puncturing of the costal transverse process to T1 target was 88.46%, to T2 target was 90.68%, and to T3 target was 90.68%, respectively. The NRS score of patients before surgery was 5.48±0.59, and those at one, four, eight, and 12 weeks after surgery were 3 (3,3), 1 (1,2), 0 (0, 1), and 0 (0, 0). The difference of NRS score between preoperation and postoperation is statistically significant. No intraoperative and postoperative complications occurred. Two patients developed PHN after standard treatment, and the incidence of it was 4.55%.

Conclusion

CT-guided puncturing of the costal transverse process in the dorsal root ganglion of patients who underwent pulsed radiofrequency treatment of T1–T3 herpes zoster neuralgia showed a high success rate and is considered to be safe and effective.

[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.

Analgesic effect of gum chewing in patients with burning mouth syndrome

The cause of burning mouth syndrome (BMS) is unknown. Although no effective treatment has been established, BMS patients frequently chew gum to alleviate pain. To identify the cause and new treatments for BMS, this study investigated the psychophysical and pharmacological properties of gum chewing to better understand its pain-relieving effects. In this prospective, blinded study, plasma catecholamine and serotonin levels and Profile of Mood States (POMS) scores were assessed after gum chewing or simulated chewing in 40 women (20 BMS patients and 20 age-matched controls). Visual analogue scale (VAS) scores for pain decreased significantly in BMS patients after gum chewing and simulated chewing. Moreover, resting VAS scores of BMS patients were significantly positively correlated with plasma adrenaline level. Furthermore, gum chewing was significantly correlated with lower plasma adrenaline level, VAS score, and tension-anxiety score. These results suggest that adrenaline is important in the pathogenesis of BMS pain and that the analgesic effect of gum chewing is induced through the potential effects of anxiety reduction, although this effect might not be specific to BMS. In addition, the analgesic effect of gum chewing was not induced solely by chewing motion.

Efficacy of extracorporeal shockwave therapy in the treatment of postherpetic neuralgia: A pilot study

Established conventional treatments for postherpetic neuralgia (PHN) and postherpetic itch (PHI) are difficult and often disappointing. In this study, the authors investigated the effect and mechanisms of extracorporeal shockwave therapy (ESWT) on pain and itch associated with PHN and PHI.Thirteen patients, 50 to 80 years of age, with symptoms associated with PHN or PHI (duration of persistent pain >3 months) and complaints of pain or itch rated >4 on a numerical rating scale (NRS), were included. ESWT was administered using a shockwave device (Piezo Shockwave, Richard Wolf GmbH, Knittlingen, Germany) to skin areas affected by pain or itch. An energy flux density of 0.09 to 0.16 mJ/mm at a frequency of 5 Hz and 2000 impulses was administered at 3-day intervals for 6 sessions. The NRS, 5D-Itch Scale, and Patients Global Impression of Change (PGIC) scale were used to evaluate the efficacy of ESWT.NRS scores of pain and itch and 5D-Itch Scale scores decreased significantly compared with before treatment and at the end of the treatment sessions (P < .0001, P = .001, P = .0002, respectively). There was a statistically significant difference between PGIC scores, which were checked every 2 sessions (P < .0001).ESWT is a noninvasive modality that significantly reduced PHN-associated pain and itch.

Somatosensory changes in Chinese patients after coronectomy vs. total extraction of mandibular third molar: a prospective study

Objectives

This study aimed to quantitatively compare the somatosensory function changes of inferior alveolar nerve (IAN) after mandibular third molar extraction with a surgery protocol of coronectomy, as opposed to the conventional method.

Materials and methods

Patients with a lower third molar directly contacting IAN were recruited and assigned either to a test group (coronectomy group) or a control group (conventional extraction). A standardized quantitative sensory testing (QST) battery was performed for four times: one week before surgery and the second, seventh, and 28th days after surgery. Z-scores and the loss/gain coding system were applied for each participant.

Results

A total of 140 molars (test group: n = 91, control group: n = 49) were enrolled. The sensitivity of the mechanical detection threshold (MDT) and pressure pain threshold (PPT) significantly increased after surgery more than before surgery in both groups (P ≤ 0.001). After the surgery, the sensitivities of the cold detection threshold (CDT), cold pain threshold (CPT), and heat pain threshold (HPT) were significantly higher in the test group than in the control group (P ≤ 0.027). The risk of IANI was significantly larger (P = 0.041) in the test group than in the control group.

Conclusions

QST was a sensitive way to detect somatosensory abnormalities even with no subjective complaint caused by surgery. Coronectomy had less influence on IAN function than conventional total extraction.

Clinical relevance

The somatosensory function changes after mandibular third molar extraction were quantitatively studied, and coronectomy was proved a reliable alternation to reduce IAN injury rate.

Test-Retest and Inter-Examiner Reliability of a Novel Bedside Quantitative Sensory Testing Battery in Postherpetic Neuralgia Patients

In health and disease, the somatosensory system has been interrogated with standardized research techniques, collectively referred to as quantitative sensory testing (QST). In neuropathic pain, QST has been used to characterize multiple sensory derangements. However, the use of QST outside the lab has been limited by several factors, including a lack of standardization, variability in procedural technique, and duration of testing that would be unacceptable for clinic. To address these shortcomings, the Neuropathic Pain Research Consortium designed an easy and low-cost "bedside" QST procedure. To test the hypothesis that this procedure would be clinically reliable over time and across different examiners, a multisite, blinded study was performed in subjects with postherpetic neuralgia. Generally, agreement between 2 examiners and over 2 study visits with 1 examiner was high. Additionally, intraclass correlation coefficients and Kappa statistics calculated showed that the battery of QST tests included were highly reliable. Interestingly, mechanical modalities (light brush, pinprick, pressure, and vibration) showed the highest reliability. The least reliable modalities were cool (room temperature) and warmth (38°C). These data demonstrate that the Neuropathic Pain Research Consortium beside QST protocol is reliable across examiner and over time, providing a validated QST tool for use in clinical practice and clinical trials. PERSPECTIVE: This blinded, multicenter trial in 32 patients with postherpetic neuralgia demonstrates bedside QST is reliable and suitable as a clinical trial outcome. The novel bedside battery could be used in clinical trials or in clinical practice over time given the reliability data presented in this article.

Itch Processing in the Skin

Itching can result from activity of specialized primary afferent neurons (“pruriceptors”) that have been shown to express certain molecular markers such as B-type natriuretic peptide and several members of the Mrgpr-family in rodents. On the other hand, neurons involved in pain processing (“nociceptors”) can also provoke itching when the activation site is restricted to an isolated tiny spot within the epidermis. Individuals classified as having sensitive skin report increased itching and pain sensations upon weak external stimuli that are not painful or itchy in the control group. Numerous possible factors could contribute to sensitive skin along the pathway of transduction of the external stimuli into peripheral neuronal signals, followed by neuronal processing, finally resulting in the perception: (a) reduced local protective factors leading to impaired skin barrier function, (b) increased production of excitatory skin mediators, (c) sensitized peripheral neurons, (d) facilitated spinal and central processing, and (e) reduced descending inhibition from the central nervous system. For all of those pathophysiological mechanisms there are clinical examples such as atopic dermatitis (a,b,c), neuropathic itching (c,e), and restless leg syndrome (d,e). However, none of these factors have been directly linked to the occurrence of sensitive skin. Moreover, individuals reporting sensitive skin are heterogeneous and a subpopulation with defined pathophysiology has not yet been identified. Given that the condition is reported in about 50% of women, and thereby includes many healthy individuals, it appears problematic to assign a definitive pathophysiological mechanism to it.

Neuropathic itch

Neuropathic itch is clinically important but has received much less attention as compared to neuropathic pain. In the past decade, itch-specific pathways have been characterized on a cellular and molecular level, but their exact role in the pathophysiology of neuropathic itch is still unclear. Traditionally, mutually exclusive theories for itch such as labeled line, temporal/spatial pattern, or intensity theory have been proposed, and experimental studies in mice mainly favor the specificity theory of itch. By contrast, results in humans also suggest a role for spatial and temporal patterns in neuropathic itch. Rarefication of skin innervation in neuropathy could provide a "spatial contrast" discharge pattern, and axotomy could induce de novo expression of the itch-specific spinal neuropeptide, gastrin-releasing peptide, in primary afferent nociceptors, thereby modulating itch processing in the dorsal horn. Thus, clinical neuropathy may generate itch by changes in the spatial and temporal discharge patterns of nociceptors, hijacking the labeled line processing of itch and abandoning the canonical scheme of mutual exclusive itch theories. Moreover, the overlap between itch and pain symptoms in neuropathy patients complicates direct translation from animal experiments and, on a clinical level, necessitates collaboration between medical specialities, such as dermatologists, anesthesiologists, and neurologists.