Allodynia and pinprick hypesthesia in acute herpes zoster, and the development of postherpetic neuralgia

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.

A Guide to Preclinical Models of Zoster-Associated Pain and Postherpetic Neuralgia

Reactivation of latent varicella-zoster virus (VZV) causes herpes zoster (HZ), which is commonly accompanied by acute pain and pruritus over the time course of a zosteriform rash. Although the rash and associated pain are self-limiting, a considerable fraction of HZ cases will subsequently develop debilitating chronic pain states termed postherpetic neuralgia (PHN). How VZV causes acute pain and the mechanisms underlying the transition to PHN are far from clear. The human-specific nature of VZV has made in vivo modeling of pain following reactivation difficult to study because no single animal can reproduce reactivated VZV disease as observed in the clinic. Investigations of VZV pathogenesis following primary infection have benefited greatly from human tissues harbored in immune-deficient mice, but modeling of acute and chronic pain requires an intact nervous system with the capability of transmitting ascending and descending sensory signals. Several groups have found that subcutaneous VZV inoculation of the rat induces prolonged and measurable changes in nociceptive behavior, indicating sensitivity that partially mimics the development of mechanical allodynia and thermal hyperalgesia seen in HZ and PHN patients. Although it is not a model of reactivation, the rat is beginning to inform how VZV infection can evoke a pain response and induce long-lasting alterations to nociception. In this review, we will summarize the rat pain models from a practical perspective and discuss avenues that have opened for testing of novel treatments for both zoster-associated pain and chronic PHN conditions, which remain in critical need of effective therapies.

Varicella-zoster virus early infection but not complete replication is required for the induction of chronic hypersensitivity in rat models of postherpetic neuralgia

Herpes zoster, the result of varicella-zoster virus (VZV) reactivation, is frequently complicated by difficult-to-treat chronic pain states termed postherpetic neuralgia (PHN). While there are no animal models of VZV-induced pain following viral reactivation, subcutaneous VZV inoculation of the rat causes long-term nocifensive behaviors indicative of mechanical and thermal hypersensitivity. Previous studies using UV-inactivated VZV in the rat model suggest viral gene expression is required for the development of pain behaviors. However, it remains unclear if complete infection processes are needed for VZV to induce hypersensitivity in this host. To further assess how gene expression and replication contribute, we developed and characterized three replication-conditional VZV using a protein degron system to achieve drug-dependent stability of essential viral proteins. Each virus was then assessed for induction of hypersensitivity in rats under replication permissive and nonpermissive conditions. VZV with a degron fused to ORF9p, a late structural protein that is required for virion assembly, induced nocifensive behaviors under both replication permissive and nonpermissive conditions, indicating that complete VZV replication is dispensable for the induction of hypersensitivity. This conclusion was confirmed by showing that a genetic deletion recombinant VZV lacking DNA packaging protein ORF54p still induced prolonged hypersensitivities in the rat. In contrast, VZV with a degron fused to the essential IE4 or IE63 proteins, which are involved in early gene regulation of expression, induced nocifensive behaviors only under replication permissive conditions, indicating importance of early gene expression events for induction of hypersensitivity. These data establish that while early viral gene expression is required for the development of nocifensive behaviors in the rat, complete replication is dispensable. We postulate this model reflects events leading to clinical PHN, in which a population of ganglionic neurons become abortively infected with VZV during reactivation and survive, but host signaling becomes altered in order to transmit ongoing pain.

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.

Can self-reported pain characteristics and bedside test be used for the assessment of pain mechanisms? An analysis of results of neuropathic pain questionnaires and quantitative sensory testing

Hyperalgesia and allodynia are frequent in neuropathic pain. Some pain questionnaires such as the Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) and the Neuropathic Pain Scale (NPS) include self-assessment or bedside testing of hyperalgesia/allodynia. The aim of this study was to determine to what extent LANSS and NPS data are congruent with findings on quantitative sensory testing (QST). Self-reported presence of dynamic mechanical allodynia (DMA) and descriptors of hot, cold, or deep ongoing pain (the NPS and LANSS) as well as bedside findings of mechanical allodynia (LANSS) were compared with signs of DMA and thermal hyperalgesia on QST in 617 patients with neuropathic pain. Self-reported abnormal skin sensitivity (LANSS) showed a moderate concordance with DMA during bedside test (67.9%, κ = 0.391) or QST (52.8%, κ = 0.165). Receiver operating curve analysis for self-reported DMA yielded similar area-under-the-curve values for the LANSS (0.65, confidence interval: 0.59%-0.97%) and NPS (0.71, confidence interval: 0.66%-0.75%) with high sensitivity but low specificity. Self-reported deep pain intensity was higher in patients with blunt pressure hyperalgesia, but not in patients with DMA or thermal hyperalgesia. No correlations were observed between self-reported hot or cold pain quality and thermal hyperalgesia on QST. Self-reported abnormal skin sensitivity has a high sensitivity to identify patients with DMA, but its low specificity indicates that many patients mean something other than DMA when reporting this symptom. Self-reported deep pain is related to deep-tissue hypersensitivity, but thermal qualities of ongoing pain are not related to thermal hyperalgesia. Questionnaires mostly evaluate the ongoing pain experience, whereas QST mirrors sensory functions. Therefore, both methods are complementary for pain assessment.

Neuropathic Pain: From Mechanisms to Treatment

Neuropathic pain caused by a lesion or disease of the somatosensory nervous system is a common chronic pain condition with major impact on quality of life. Examples include trigeminal neuralgia, painful polyneuropathy, postherpetic neuralgia, and central poststroke pain. Most patients complain of an ongoing or intermittent spontaneous pain of, for example, burning, pricking, squeezing quality, which may be accompanied by evoked pain, particular to light touch and cold. Ectopic activity in, for example, nerve-end neuroma, compressed nerves or nerve roots, dorsal root ganglia, and the thalamus may in different conditions underlie the spontaneous pain. Evoked pain may spread to neighboring areas, and the underlying pathophysiology involves peripheral and central sensitization. Maladaptive structural changes and a number of cell-cell interactions and molecular signaling underlie the sensitization of nociceptive pathways. These include alteration in ion channels, activation of immune cells, glial-derived mediators, and epigenetic regulation. The major classes of therapeutics include drugs acting on α₂δ subunits of calcium channels, sodium channels, and descending modulatory inhibitory pathways.

Local Administration of Methylcobalamin for Subacute Ophthalmic Herpetic Neuralgia: A Randomized, Phase III Clinical Trial

OBJECTIVES

The ophthalmic branch of the trigeminal nerve is one of the most frequently involved sites of postherpetic neuralgia. A single-center randomized controlled study was conducted to evaluate the efficacy of local methylcobalamin injection for subacute ophthalmic herpetic neuralgia (SOHN).

METHODS

One hundred and five patients with a pain score of 4 or greater were randomized to receive a combination of methylcobalamin and lidocaine via local injection (LM group, n = 35), intramuscular methylcobalamin and local lidocaine injection (IM group, n = 35), and oral methylcobalamin tablet and lidocaine local injection (OM group, n = 35) for 4 weeks. Multilevel mixed modeling was employed to examine treatment responses.

RESULTS

Pain scores were reduced in all groups, but this reduction was significantly greater in the LM group (6.7 at baseline vs. 2.8 at endpoint) when compared with systemic administration (IM group 6.8 vs. 4.9, OM group 6.7 vs. 5.1). Clinically relevant reduction of pain (>30%) was seen in 91% of patients in the LM group, a significantly greater proportion than in the systemic groups (66% IM group, 57% OM group). Analgesic use reduced significantly in the LM group (94% at baseline vs. 6% at endpoint) but not in systemic groups (IM group 97% vs. 86%, OM group 94% vs. 80%). Health-related quality of life was higher in the LM group than in the systemic groups. In mixed modelling, increased age was associated with a lower response to methylcobalamin.

CONCLUSIONS

This study indicates that local injection of methylcobalamin produces significant pain relief from SOHN and is superior to systemic administration.

Somatosensory profiles in acute herpes zoster and predictors of postherpetic neuralgia

This prospective cohort study aimed to characterize the sensory profile during acute herpes zoster (AHZ) and to explore sensory signs as well as physical and psychosocial health as predictors for postherpetic neuralgia (PHN). Results of quantitative sensory testing of 74 patients with AHZ at the affected site and at the distant contralateral control site were compared to a healthy control group. Pain characteristics (Neuropathic Pain and Symptom Inventory and SES), physical functioning, and psychosocial health aspects (Pain Disability Index, SF-36, and STAI) were assessed by questionnaires. Patients with PHN (n = 13) at 6-month follow-up were compared to those without PHN (n = 45). Sensory signs at the affected site were thermal and vibratory hypesthesia, dynamic mechanical allodynia (DMA), pressure hyperalgesia, and high wind-up (18%-29%), as well as paradoxical heat sensations and pinprick hypalgesia (13.5%). The unaffected control site exhibited thermal and vibratory hypesthesia, DMA, and pressure hyperalgesia. Dynamic mechanical allodynia and pinprick hypalgesia were mutually exclusive. Postherpetic neuralgia was associated with DMA (38.5% vs 6.7%; P = 0.010) and vibratory hypesthesia (38.5% vs 11.1%; P = 0.036) at the control site, with mechanical gain and/or loss combined with normal thermal detection (affected site: 69.2% vs 31.1%; P = 0.023; control site: 53.8% vs 15.5%; P = 0.009). Pain Disability Index (P = 0.036) and SES affective pain perception scores (P = 0.031) were over 50% higher, and 6 of 8 SF-36 subscores were over 50% lower (P < 0.045) in PHN. Sensory profiles in AHZ indicate deafferentation and central but not peripheral sensitization. Sensory signs at distant body sites, strong affective pain perception, as well as reduced quality of life and physical functioning in the acute phase may reflect risk factors for the transition to PHN.

Dynamic of the somatosensory system in postherpetic neuralgia

Introduction:

In postherpetic neuralgia (PHN) different types of patients can be distinguished regarding their predominant peripheral nociceptor function.

Objective:

The aim was to examine somatosensory profiles in the course of disease with special regard to the different subtypes existing in PHN.

Methods:

Twenty patients with PHN (7 men and 13 women, age 67 ± 9.6 years) were examined at baseline (disease duration 18.1 ± 26 months) and follow-up (31.6 ± 23.8 months later) with quantitative sensory testing (protocol of the German Research Network on Neuropathic Pain).

Results:

Fourteen (70%) PHN patients presented with impaired (iPHN) and 6 (30%) with preserved (pPHN) C-fiber function. Groups did not differ regarding age, disease duration, or pain intensity at baseline. Both groups did not differ regarding change in pain intensity (−0.5 ± 2.3 vs −1.7 ± 2.6 numerical rating scale, P = n.s.) at follow-up. Impaired PHN improved in thermal and mechanical detection thresholds as well as allodynia independent from change in pain intensity. By contrast, pPHN showed an increase in mechanical pain sensitivity (1.4 ± 2.5 vs −0.4 ± 2.2, P < 0.05) and a trend towards a stronger loss of detection (66% vs 33%, P = n.s.) on follow-up.

Conclusion:

Results demonstrate that patients with preserved C-fiber function are more predisposed to develop signs of central sensitization as demonstrated by an increased mechanical pain sensitivity. Impaired C-fiber function is able to improve even in chronic cases, but a functional loss is unlikely to play a role here. The knowledge of development of somatosensory profiles in the course of the disease offers possibilities to optimize a mechanism-based treatment.

Other facial neuralgias

Premise In this article we review some lesser known cranial neuralgias that are distinct from trigeminal neuralgia, trigeminal autonomic cephalalgias, or trigeminal neuropathies. Included are occipital neuralgia, superior laryngeal neuralgia, auriculotemporal neuralgia, glossopharyngeal and nervus intermedius neuralgia, and pain from acute herpes zoster and postherpetic neuralgia of the trigeminal and intermedius nerves. Problem Facial neuralgias are rare and many physicians do not see such cases in their lifetime, so patients with a suspected diagnosis within this group should be referred to a specialized center where multidisciplinary team diagnosis may be available. Potential solution Each facial neuralgia can be identified on the basis of clinical presentation, allowing for precision diagnosis and planning of treatment. Treatment remains conservative with oral or topical medication recommended for neuropathic pain to be tried before more invasive procedures are undertaken. However, evidence for efficacy of current treatments remains weak.

A systematic review and meta-analysis of risk factors for postherpetic neuralgia

Supplemental Digital Content is Available in the Text.

Patients with herpes zoster can develop persistent pain after rash healing, a complication known as postherpetic neuralgia. By preventing zoster through vaccination, the risk of this common complication is reduced. We searched MEDLINE and Embase for studies assessing risk factors for postherpetic neuralgia, with a view to informing vaccination policy. Nineteen prospective studies were identified. Meta-analysis showed significant increases in the risk of postherpetic neuralgia with clinical features of acute zoster including prodromal pain (summary rate ratio 2.29, 95% confidence interval: 1.42-3.69), severe acute pain (2.23, 1.71-2.92), severe rash (2.63, 1.89-3.66), and ophthalmic involvement (2.51, 1.29-4.86). Older age was significantly associated with postherpetic neuralgia; for individual studies, relative risk estimates per 10-year increase ranged from 1.22 to 3.11. Evidence for differences by gender was conflicting, with considerable between-study heterogeneity. A proportion of studies reported an increased risk of postherpetic neuralgia with severe immunosuppression (studies, n = 3/5) and diabetes mellitus (n = 1/4). Systemic lupus erythematosus, recent trauma, and personality disorder symptoms were associated with postherpetic neuralgia in single studies. No evidence of higher postherpetic neuralgia risk was found with depression (n = 4) or cancer (n = 5). Our review confirms a number of clinical features of acute zoster are risk factors for postherpetic neuralgia. It has also identified a range of possible vaccine-targetable risk factors for postherpetic neuralgia; yet aside from age-associated risks, evidence regarding risk factors to inform zoster vaccination policy is currently limited.

Efficacy of continuous epidural block in acute herpes zoster: Incidence and predictive factors of postherpetic neuralgia, a retrospective single-center study

The aim of the present study was to investigate efficacy of continuous epidural block for prevent postherpetic neuralgia (PHN) progression in cases of acute herpes zoster with severe pain and also to identify predictive factors for PHN in such conditions.We retrospectively analyzed the clinical data of patients with herpes zoster who underwent continuous epidural block between March 2013 and October 2015. Time points were set as 1 month, 3 months, and 6 months after zoster onset. PHN was defined as the presence of pain with NRS ≥3 at certain time points.The incidence of developing PHN was 38.1%, 27.0%, and 19.0% 1 month, 3 months, and 6 months after zoster onset, respectively. Age and duration of catheterization were predictive factors for PHN at 1 month. Age, duration of catheterization, and NRS at first visit were identified as predictive factors for PHN at 3 months. Presence of diabetes, duration of catheterization, and NRS during catheterization were significant predictive factors for PHN at 6 months.The incidence of PHN is higher in zoster patients with severe pain that requires continuous epidural block compared to incidence in the general population. Advanced age and severe initial pain intensity were predictive factors of PHN development. Prolonged catheterization resulting from weak response to treatment strongly suggested progression to PHN.

Predictors of postherpetic neuralgia in patients with herpes zoster: a pooled analysis of prospective cohort studies from North and Latin America and Asia

OBJECTIVES

The most common complication of herpes zoster (HZ) is postherpetic neuralgia (PHN), a persistent pain that can substantially affect quality of life (QoL). This analysis aimed to evaluate predictors of PHN in HZ patients.

METHODS

A pooled analysis of prospective cohort studies of HZ patients aged ≥ 50 years from North America (Canada), Latin America (Brazil, Mexico, and Argentina), and Asia (Taiwan, South Korea, and Thailand) was performed. Patients within 14 days of rash onset were included. The incidence of PHN was defined as a worst pain score of ≥ 3, persisting/appearing at >90 days after rash onset. Socio-demographics, HZ disease characteristics, treatment, pain-related interference with activities of daily living, and health-related QoL were assessed.

RESULTS

Of 702 patients with HZ, 148 (21.1%) developed PHN. Similar risks of PHN were observed across geographic regions. On multivariate analysis, older age, greater severity of pain at rash onset, employment status, walking problems at enrollment, and pain interference affecting social relationships were significantly associated with the development of PHN.

CONCLUSIONS

In addition to older age and severe acute pain, this study suggests that impaired physical and social functioning from acute zoster pain may play a role in the development of PHN in this prospective cohort study of HZ patients from North and Latin America and Asia.

Thiamine, cobalamin, locally injected alone or combination for herpetic itching: a single-center randomized controlled trial

OBJECTIVES

The present study was designed to explore the efficacy of locally injected thiamine or cobalamin in relieving itch or pain and improving the daily living activities among patients with herpetic itching.

METHODS

Eighty eligible patients with herpetic itching with a worst itching score of ≥ 4 were randomized to receive locally injected thiamine (B1 group), cobalamin (B12 group), lidocaine (LD group), or combination of thiamine and cobalamin (COB group) for 4 weeks. The treatment efficacy was assessed based on the patients' pruritus and pain severity, global impression of change, and activities of daily living and quality of life.

RESULTS

After 7 days, thiamine yielded a significant itch relief, cobalamin yielded a significant pain relief, and their combination significantly relieved both pain and itch; which all continued till the endpoint (all Ps<0.001). However, lidocaine did not provide significant itch or pain relief than the other groups. Sixteen patients in the thiamine group achieved ≥ 30% itch reduction; 18 patients in the cobalamin group obtained ≥ 30% pain reduction; and 18 patients achieved ≥ 30% itch reduction and 19 patients obtained ≥ 30% pain reduction in the combination group. The activities of daily living and quality of life data at the endpoint were consistent with a significant benefit in the thiamine (P<0.05), cobalamin, and combination groups (both Ps<0.001).

DISCUSSION

Locally injected thiamine had a significant antipruritic effect, cobalamin had an analgesic effect, and their combination had the dual effect with no obvious synergies. This intervention was efficacious, tolerable, and safe for herpetic itching.

An overview of predictors for persistent neuropathic pain

Neuropathic pain (NP) is a pain arising as a direct consequence of a lesion or disease affecting the somatosensory system. A variety of factors associated with the development of persistent NP have been suggested. The goal of the present article is to provide an overview of current knowledge about prognostic factors for persistent NP. The International Classification of Functioning, Disability and Health model is used as a framework to categorize these predictors. Most reported predictors in the literature were found in the International Classification of Functioning, Disability and Health-category of personal factors, especially age and psychological factors, functions and structure, including sensory signs and symptoms. Predictors in the category of environmental factors, activities and participation were less frequently described.

Use of S-LANSS, a tool for screening neuropathic pain, for predicting postherpetic neuralgia in patients after acute herpes zoster events: a single-center, 12-month, prospective cohort study

Postherpetic neuralgia (PHN) is one of the most severe sequelae of herpes zoster events. Several risk factors have been reported for PHN, including old age, severe skin rash, and intense pain. This study therefore aims to evaluate the usefulness of the Self-completed Leeds Assessment of Neuropathic Symptoms and Signs pain scale (S-LANSS) in conjunction with previously reported risk factors for predicting PHN. A group of herpes zoster patients (N = 305) were included in the cohort study. Subjects were asked for their demographic information, clinical symptoms and signs, intensity of pain by visual analog scale (VAS), and S-LANSS. They were followed up in clinical visits or via telephone for 12 months. Nineteen patients (6.2%) suffered from PHN in this study. Using logistic regression, 3 risk factors for PHN were identified: age ≥70 years, high VAS scores, and high S-LANSS scores. Prediction of PHN using VAS (≥8) and S-LANSS (≥15) criteria achieved a sensitivity of 78.9% and specificity of 78.0%. Prediction of PHN in elderly patients (≥70 years), using the criteria of VAS (≥6) and S-LANSS (≥15) as well, achieved 100% sensitivity and 57.1% specificity. S-LANSS could be a useful prediction tool for PHN, particularly if combined with previously well-known risk factors and VAS.

PERSPECTIVE

Among acute herpes zoster patients, subjects with characteristics of neuropathic pain showed high frequency of PHN. The tools for screening neuropathic pain like S-LANSS could be helpful for predicting PHN and enabling early intervention of pain management.

Animal models of varicella zoster virus infection

Primary infection with varicella zoster virus (VZV) results in varicella (chickenpox) followed by the establishment of latency in sensory ganglia. Declining T cell immunity due to aging or immune suppressive treatments can lead to VZV reactivation and the development of herpes zoster (HZ, shingles). HZ is often associated with significant morbidity and occasionally mortality in elderly and immune compromised patients. There are currently two FDA-approved vaccines for the prevention of VZV: Varivax® (for varicella) and Zostavax® (for HZ). Both vaccines contain the live-attenuated Oka strain of VZV. Although highly immunogenic, a two-dose regimen is required to achieve a 99% seroconversion rate. Zostavax vaccination reduces the incidence of HZ by 51% within a 3-year period, but a significant reduction in vaccine-induced immunity is observed within the first year after vaccination. Developing more efficacious vaccines and therapeutics requires a better understanding of the host response to VZV. These studies have been hampered by the scarcity of animal models that recapitulate all aspects of VZV infections in humans. In this review, we describe different animal models of VZV infection as well as an alternative animal model that leverages the infection of Old World macaques with the highly related simian varicella virus (SVV) and discuss their contributions to our understanding of pathogenesis and immunity during VZV infection.

Natural history of herpes zoster: late follow-up of 3.9 years (n=43) and 7.7 years (n=10)

Postherpetic neuralgia (PHN) is a common complication after herpes zoster (HZ). Subjects who completed a longitudinal observational 6-month study (4 visits) of the natural history of HZ were recontacted for 2 additional follow-up visits that included pain and sensory symptom assessment, quantitative sensory testing, capsaicin response test, and 3-mm punch skin biopsies in HZ-affected, mirror-image, and control skin sites. Forty-three subjects (14 with PHN at 6 months) of the original 94 subjects in the cohort were comprehensively assessed at a median 3.9 years after HZ onset (visit 5), and 10 subjects underwent a final assessment at a median 7.7 years after HZ onset (visit 6). At 3.9 years, none of the 29 subjects who had been pain free at 6 months had a recurrence of pain. Only 2 of the 14 subjects with PHN at 6 months still had pain at 3.9 years. One subject with PHN at 6 months was free of symptoms at 3.9 years but had very mild pain at 7.7 years. Sensory function continued on a path toward normalization, but was still abnormal in many subjects, especially those who met criteria for PHN at 6 months. Even at 7.7 years, reinnervation of HZ-affected skin was not apparent.

Postherpetic neuralgia: New hopes in prevention with adult vaccination and in treatment with a concentrated capsaicin patch

Background and purpose

Postherpetic neuralgia (PHN) is a complication of acute herpes zoster (HZ). The evidence base for management of PHN has increased by recent publications. Therefore, we reviewed incidence of HZ, prevalence, risk factors, and mechanism of PHN pain, prevention and treatment of PHN with special interest in studies on adult vaccination and topical application of lidocaine and concentrated capsaicin patch.

Methods

We searched databases with an English language restriction: MEDLINE 1944–2011, EMBASE 1988–2011, PubMed, and the Cochrane Controlled Trial Register and Cochrane Library (2011). From retrieved publications, we selected studies focusing on our main goals, prevention and treatment of PHN in particular. The review was therefore systematic, but with a pragmatic approach to which studies to select for closer review.

Results

From the large number of abstracts retrieved we selected 65 papers for closer review and as evidence base for our conclusions and recommendations for prevention and treatment of HZ and PHN. The incidence of HZ and risks of having PHN after HZ increases markedly with age above 60–70. Severity of symptoms and their impact on quality of life is a major health problem of persons above 70 years of age. Adult vaccination with the reinforced varicella virus vaccine reduces the incidence of HZ and PHN by about 50%. This is an important health and quality of life gain for the elderly. Antiviral drugs given early in an episode of HZ reduce pain and duration of HZ and decrease the risk of PHN.

Pharmacological management of PHN are with nortriptyline (or amitriptyline in the younger patients), and or a gabapentinoid as first line drugs. Early treatment also is with topical lidocaine for immediate but short-lasting relief of burning hyperalgesia, and topical capsaicin relieving hypersensitivity for up to 12 weeks. A number of second and third line drugs have less evidence-base for effect, and often more adverse effects than the first line drugs: serotonin and noradrenaline uptake inhibitors (venlafaxin, duloxetin), antiepileptics (valproate), and opioid analgesics. Opioids are indicated for bridging in patients with severe PHN-symptoms while waiting for the more specific first line drugs to take effect. In these elderly patients, systemic pharmacological treatments are always a difficult balance between effects and adverse effects. It is important with close supervision of the patients, especially during start-up of systemically administered drugs, in order to prevent tragic complications from falls in sedated, dizzy, and confused elderly patients. Topical treatment with lidocaine and capsaicin patches does not have these problems.

Conclusions

Prevention of this significant health problem of the increasing elderly population is now possible through adult vaccination against varicella zoster virus (VZV) reactivation, as well as vigorous and early antiviral treatment during acute HZ. The evidence -base supports the oral use of tricyclic antidepressants, gabapentinoids, and opioids for bridging till the first line drugs take effect. Topical therapy with lidocaine and capsaicin patches is effective and well supported by evidence. A number of second and third line drugs and treatments are available, but have less evidence-base. All drug treatments, except topical lidocaine and capsaicin, have adverse effects that are often problematic and can be dangerous in the elderly patients. Close supervision of the patients is mandatory.

Implications

Recent advances in prevention and management of this serious health problem should be better known and implicated: Adult vaccination for prevention of varicella zoster virus reactivation, antiviral drugs and combinations of drugs can reduce the suffering from acute HZ and chronic PHN. Topical lidocaine and capsaicin are now evidence-based therapies that reduce suffering from hypersensitivity and hyperalgesia in patients with PHN. When properly applied, they have few complications.

Laser heat stimulation of tiny skin areas adds valuable information to quantitative sensory testing in postherpetic neuralgia

Patients suffering from postherpetic neuralgia often complain about hypo- or hypersensation in the affected dermatome. The loss of thermal sensitivity has been demonstrated by quantitative sensory testing as being associated with small-fiber (Aδ- and C-fiber) deafferentation. We aimed to compare laser stimulation (radiant heat) to thermode stimulation (contact heat) with regard to their sensitivity and specificity to detect thermal sensory deficits related to small-fiber dysfunction in postherpetic neuralgia. We contrasted detection rate of laser stimuli with 5 thermal parameters (thresholds of cold/warm detection, cold/heat pain, and sensory limen) of quantitative sensory testing. Sixteen patients diagnosed with unilateral postherpetic neuralgia and 16 age- and gender-matched healthy control subjects were tested. Quantitative sensory testing and laser stimulation of tiny skin areas were performed in the neuralgia-affected skin and in the contralateral homologue of the neuralgia-free body side. Across the 5 thermal parameters of thermode stimulation, only one parameter (warm detection threshold) revealed sensory abnormalities (thermal hypoesthesia to warm stimuli) in the neuralgia-affected skin area of patients but not in the contralateral area, as compared to the control group. In contrast, patients perceived significantly less laser stimuli both in the affected skin and in the contralateral skin compared to controls. Overall, laser stimulation proved more sensitive and specific in detecting thermal sensory abnormalities in the neuralgia-affected skin, as well as in the control skin, than any single thermal parameter of thermode stimulation. Thus, laser stimulation of tiny skin areas might be a useful diagnostic tool for small-fiber dysfunction.

Natural history of sensory function after herpes zoster

The natural history of sensory function in the first 6months after herpes zoster (HZ) was determined in a cohort of 94 subjects at elevated risk for developing post-herpetic neuralgia (PHN). All four visits included ratings of pain and sensory symptoms, mapping areas of altered sensation and allodynia, and quantitative thermal and mechanical sensory testing. The last three visits included the capsaicin response test. Sensory thresholds in distant control skin were stable. Mirror-image skin was persistently hyperesthetic to warming and mechanical stimuli and hyperalgesic to heat compared to distant control skin. HZ skin showed deficits in all thermal modalities. Sensory recovery was limited and selective. Allodynia area and severity, hyperalgesia to von Frey hair, and cold detection threshold improved, but deficits to warmth and heat pain did not. Capsaicin on HZ skin significantly aggravated pain and allodynia in the majority of subjects at 6-8weeks after HZ onset. At study entry, eventual PHN subjects had significantly more impairment in detecting warmth and cold, a larger area of altered sensation, a larger area of allodynia, and more severe allodynia. The results support the study hypothesis that severity of initial injury predicts PHN, especially impaired cold sensation in HZ skin. The hypothesis that PHN develops because of a failure to recover normal neural function was not supported. Sensory recovery proceeded at the same rate in eventual pain-free and eventual PHN subjects and is not a requirement for pain resolution. Early interventions that reduce neural injury or enhance recovery should be of benefit.

Postherpetic neuralgia: from preclinical models to the clinic

Postherpetic neuralgia (PHN), a common complication of herpes zoster, which results from reactivation of varicella zoster virus, is a challenging neuropathic pain syndrome. The incidence and severity of herpes zoster and PHN increases with immune impairment or age and may become a greater burden both in terms of health economics and individual suffering. A clearer understanding of the underlying mechanisms of this disease and translation of preclinical outcomes to the clinic may lead to more efficacious treatment options. Here we give an overview of recent findings from preclinical models and clinical research on PHN.

Incremental 1-year medical resource utilization and costs for patients with herpes zoster from a set of US health plans

BACKGROUND

Nearly 1 million new episodes of herpes zoster (HZ) occur annually in the US, yet little is known about the medical resource utilization (RU) and costs associated with HZ and its complications.

OBJECTIVES

To describe the medical RU and cost burden of HZ in the first 90 days and the first year after diagnosis from the health insurer perspective and to stratify this burden for patients diagnosed with post-herpetic neuralgia (PHN) and those who are immunocompromised. In addition, this study explores costs from the societal perspective as a result of work loss in the first year after diagnosis.

METHODS

The medical RU and cost data were obtained from the MarketScan Research Database for the years 1998-2003. This database contains inpatient, outpatient and prescription drug data for approximately 14 million individuals of all ages, covered under a variety of fee-for-service and capitated provider reimbursement arrangements, including those with Medicare and private insurance. The work loss estimates were based on the MarketScan Health and Productivity Management Database. Claims for services incurred between 1 January 1998 and 31 December 2003 were screened to identify a cohort of HZ patients based on the presence of at least one International Classification of Diseases, 9th Revision (ICD-9) diagnosis code 053.xx. Each patient was assigned an index date based on the earliest observed occurrence of an HZ diagnosis. A cohort of PHN patients was identified as a subset of the HZ cohort with ICD-9 codes 053.12, 053.13, 053.19 or 729.2x in the period of 90 days to 12 months after the index date. Multivariable regression was used to compare HZ cases with matched controls after adjusting for demographic characteristics, insurance status, co-morbidities and medical expenditure in the 6 months prior to diagnosis for each of the endpoints. Separate regression models were developed, in which age and immune status were stratified. All costs were adjusted to March 2008 values using the medical care component of the Consumer Price Index. The average per patient cost of all HZ cases was $US605 in the first 90 days after diagnosis and $US1052 at 1 year. For the subset with PHN, the average per patient cost of HZ at 1 year was $US3815. For the subset with an immunocompromising condition, the average HZ cost at 1 year was $US1745. The majority of the costs were the result of outpatient visits and prescription drugs. The subset of HZ cases that had both absence hour and short-term disability (STD) records available had 26.5 absence hours and 2.9 STD days. Healthcare utilization, medical care costs and work loss all increased with age for all HZ cases. Based on the results from the present study, the direct medical cost burden of HZ in the US is high, exceeding $US1000 per HZ patient. This direct medical cost may be nearly twice as high in immunocompromised patients and four times as high in the subset of HZ cases with PHN. The direct medical cost burden of HZ may exceed $US1 billion annually in the US. The majority of medical RU and cost burden is incurred by the elderly. Although many people with HZ may no longer be in the workforce, HZ does contribute to lost work time.

Pregabalin for postherpetic neuralgia: placebo-controlled trial of fixed and flexible dosing regimens on allodynia and time to onset of pain relief

Time to onset of pain relief and improvement in allodynia in 269 patients with postherpetic neuralgia was examined in a 4-week randomized trial comparing flexibly dosed pregabalin (150-600 mg/d), fixed-dose pregabalin (300 mg/d), and placebo. For each patient with clinically meaningful pain reduction (>or=30%) at end point, onset of pain relief was defined as the first study day on which a patient reported >or=1-point reduction in pain relative to baseline. Average dose achieved was 396 mg/d in the flexible-dose group compared with 295 mg/d in the fixed-dose group. Median pain relief onset times were 3.5 days (flexible-dose), 1.5 days (fixed-dose), and >4 weeks (placebo). Compared with placebo, significantly more patients in both pregabalin treatment groups achieved >or=30% and >or=50% pain reduction at end point. Almost 95% of patients had brush-evoked allodynia, with 68% having moderate to severe allodynia (>or=40/100 mm). At baseline, pain and allodynia were highly correlated. Independent of treatment assignment, improvement in pain and improvement in allodynia were significantly correlated. Allodynia could serve as a useful surrogate outcome measure in future studies. Pregabalin was significantly better than placebo in alleviating allodynia (flexible-dose reduction, 26 mm; fixed-dose, 21 mm; placebo, 12 mm). Discontinuation rates due to adverse events were more frequent in the fixed-dose group.

PERSPECTIVE

A flexible-dose regimen reduces discontinuations, facilitates higher final doses, and results in a slightly greater pain relief. Allodynia (touch-evoked pain) can be of disabling severity and is present in nearly all patients with postherpetic neuralgia. Allodynia severity is correlated with pain severity and improvement in allodynia is correlated with clinical response.

The impact of the varicella vaccination program on herpes zoster epidemiology in the United States: a review

Speculation that a universal varicella vaccination program might lead to an increase in herpes zoster (HZ) incidence has been supported by modeling studies that assume that exposure to varicella boosts immunity and protects against reactivation of varicella-zoster virus (VZV) as HZ. Such studies predict an increase in HZ incidence until the adult population becomes predominantly composed of individuals with vaccine-induced immunity who do not harbor wild-type VZV. In the United States, a varicella vaccination program was implemented in 1995. Since then, studies monitoring HZ incidence have shown inconsistent findings: 2 studies have shown no increase in overall incidence, whereas 1 study has shown an increase. Studies from Canada and the United Kingdom have shown increasing rates of HZ incidence in the absence of a varicella vaccination program. Data suggest that heretofore unidentified risk factors for HZ also are changing over time. Further studies are needed to identify these factors, to isolate possible additional effects from a varicella vaccination program. Untangling the contribution of these different factors on HZ epidemiology will be challenging.

Natural history and treatment of herpes zoster

The objective of this article is to provide an overview of the natural history and treatment of herpes zoster, with a focus on pain management. Herpes zoster has the highest incidence of all neurological diseases, occurring annually in approximately 1 million people in the United States. A basic feature of herpes zoster is a marked increase in incidence with aging and with diseases and drugs that impair cellular immunity. Herpes zoster begins with reactivation of varicella zoster virus in dorsal root or cranial nerve ganglia, which is often accompanied by a prodrome of dermatomal pain or abnormal sensations. Varicella zoster virus spreads in the affected primary afferent nerve to the skin and produces a characteristic dermatomal maculopapular and vesicular rash and pain. Herpes zoster acute pain lowers quality of life and interferes with activities of daily living. Antiviral therapy and scheduled analgesics form the pharmacotherapeutic foundation for herpes zoster acute pain reduction. If moderate to severe herpes zoster pain is not adequately relieved by antiviral agents in combination with oral analgesic medications, then corticosteroids, anticonvulsants (eg, gabapentin or pregabalin), tricyclic antidepressants (eg, nortriptyline or desipramine), or neural blockade can be considered.

PERSPECTIVE

This article presents information on the clinical features and treatment of herpes zoster. This information will help clinicians diagnose and manage herpes zoster pain.

Postherpetic neuralgia: epidemiology, pathophysiology and management

Postherpetic neuralgia (PHN) is a neuropathic pain syndrome and is the most common complication of herpes zoster (HZ; shingles). PHN occurs mainly in HZ patients 60 years of age and older, in particular in those suffering from more severe acute pain and rash. Administration of antiviral drugs reduces the duration of pain associated with HZ. The pathophysiology of PHN may be distinctly different between patients with either reduced or increased skin sensitivity. Therapy is with tricyclic drugs (e.g., nortriptyline), alpha 2 delta-ligands (e.g., gabapentin) or opiates with adjunctive topical lidocaine or capsaicin. Mechanism-based therapy is a desirable goal but so far proves elusive. The incidence of HZ, and therefore that of PHN, is likely to increase as a result of greater longevity and increasing numbers of patients receiving treatment that compromises cell-mediated immunity. A zoster vaccine for administration to adults reduces the incidence of HZ and PHN, as well as the burden of illness associated with these conditions.

Evaluation of the cost-effectiveness in the United States of a vaccine to prevent herpes zoster and postherpetic neuralgia in older adults

CONTEXT

A live-attenuated varicella-zoster virus vaccine, demonstrated to reduce the incidence of herpes zoster (HZ) and postherpetic neuralgia (PHN) and the morbidity associated with incident HZ and its sequelae, has recently been approved for use in the United States (U.S.).

OBJECTIVE

To examine the potential value of zoster vaccine for society and payers. DESIGN, SETTING AND POPULATION: An age-specific decision analytic model was designed to estimate the lifetime costs and outcomes associated with HZ, PHN and other HZ-related complications for vaccinated and non-vaccinated cohorts aged >or=60 years. Clinical trial data, published literature and other primary studies were used to inform the model. Robustness of results to key model parameters was explored through a series of one-way, multivariate and probabilistic sensitivity analyses. Both societal and payer perspectives were considered.

MAIN OUTCOME MEASURE

Incremental cost per quality-adjusted life year (QALY) gained.

RESULTS

For a representative cohort of 1,000,000 U.S. vaccine recipients aged >or=60 years, use of the zoster vaccine was projected to eliminate 75,548-88,928HZ cases and over 20,000 PHN cases. Over 300,000 outpatient visits, 375,000 prescriptions, 9,700 ER visits and 10,000 hospitalizations were projected to be eliminated with the vaccine translating into savings of US$ 82 million to US$ 103 million in healthcare costs associated with the diagnosis and treatment of HZ, PHN and other HZ-related complications. Cost-effectiveness ratios range from US$ 16,229 to US$ 27,609 per QALY gained, depending on the input data source and analytic perspective. Results were most sensitive to PHN costs, duration of vaccine efficacy, vaccine efficacy against PHN and HZ, QALY loss associated with pain states and complication costs.

CONCLUSIONS

The zoster vaccine at a price of US$ 150 is likely to be cost-effective for a cohort of immunocompetent U.S. vaccine recipients aged >or=60 years using commonly cited thresholds for judging cost-effectiveness. Conclusions are robust over plausible ranges of input parameter values and a broad range of scenarios and age cohorts.

[Pain associated with craniofacial and cervical herpes zoster]

Ophthalmological and cervical involvement of herpes zoster virus ranks second and third, respectively, in terms of localization frequency. Involvement of the cranial nerves is a particular sign of complications, notably ocular complications, possibly compromising the visual or facial prognosis through involvement of the VIIth nerve, which is responsible for facial paralysis. These types of involvement should be rapidly diagnosed and treated so as to limit these complications. The pain associated with herpes zoster remains frequent and difficult to treat, even if today the criteria for defining postzoster pain is increasingly refined. Antalgic and antiviral treatment should be initiated early, from the very first signs, to attempt to reduce the incidence of this postzoster pain. The risk factors, associated with the development of postzoster pain are age over 50 years, the severity of the skin rash and the intensity of the acute pain, and the existence of a prodromic pain phase before onset. The European Federation of Neurological Societies has recently published guidelines on the pharmacological treatments for postzoster pain. Nerve block treatments remain at a limited evidence level. Patients with postzoster pain should be managed by teams specializing in pain management as soon as conventional treatments fail.

Clinical and psychosocial correlates of acute pain in herpes zoster

BACKGROUND

Acute and persistent pain are the most significant clinical manifestations of herpes zoster (HZ), but the characteristics of acute pain in HZ patients have been inadequately investigated.

OBJECTIVES

To correlate the severity of acute pain with clinical, demographic and psychosocial characteristics of HZ patients.

STUDY DESIGN

Five hundred thirty-three patients with acute HZ were recruited by 119 dermatologists who collected medical and demographic data at diagnosis, provided counselling and therapy where appropriate and asked the patients to complete the Short Italian Questionnaire designed for comprehensive evaluation of HZ patients.

RESULTS

In a univariate analysis, greater acute pain severity was significantly associated with female gender, number of dermatomes affected, presence of prodromal pain, abnormal sensations (dysesthesia), education level, anxiety and depression. Quality of life, even if greatly reduced, did not correlate with the intensity of pain. In a multivariate model, the intensity of pain was independently associated with the extent of rash (p=0.042), presence of prodromal pain (p=0.005), dysesthesia, education level (p=0.040), and depression (p<0.001), but not with gender, anxiety or quality of life.

CONCLUSIONS

This study suggests that in patients with acute HZ the severity of the disease and depression at presentation are the main correlates of pain intensity.

Recommendations for the management of herpes zoster

The objective of this article is to provide evidence-based recommendations for the management of patients with herpes zoster (HZ) that take into account clinical efficacy, adverse effects, impact on quality of life, and costs of treatment. Systematic literature reviews, published randomized clinical trials, existing guidelines, and the authors' clinical and research experience relevant to the management of patients with HZ were reviewed at a consensus meeting. The results of controlled trials and the clinical experience of the authors support the use of acyclovir, brivudin (where available), famciclovir, and valacyclovir as first-line antiviral therapy for the treatment of patients with HZ. Specific recommendations for the use of these medications are provided. In addition, suggestions are made for treatments that, when used in combination with antiviral therapy, may further reduce pain and other complications of HZ.

Acute/subacute herpes zoster: healthcare resource utilisation and costs in a group of US health plans

BACKGROUND

Although there are estimated to be nearly 1 million cases of herpes zoster diagnosed in the US each year, the economic costs associated with herpes zoster in the US have not been well described.

OBJECTIVE

To describe the healthcare resource utilisation and costs associated with physician-diagnosed acute/subacute herpes zoster, from a payer perspective, using a large US healthcare claims database.

METHODS

Data for the period 2000-1 were obtained from the Medstat Marketscan healthcare claims database. The duration of acute/subacute herpes zoster was considered to include the 21 days preceding, and 90 days following, the initial herpes zoster diagnosis. Resource utilisation was examined for individuals with newly diagnosed acute/subacute herpes zoster (n = 8741) and compared, through regression analyses, with that observed for control individuals from the same population (n = 50,000). Similar analyses were conducted for costs; the costs included reflected healthcare payments from patients, insurers and other sources. Regression analyses controlled for demographics (age, gender), conditions that have been observed with greater frequency among patients with acute/subacute herpes zoster in prior studies (cancer, HIV infection, organ transplantation, other immunosuppressive conditions and therapies) and the number of billed services within each of seven categories of care that were potentially related to acute/subacute herpes zoster and that were utilised within the 30-180 days prior to the diagnosis for affected patients, and over an analogous period for controls.

RESULTS

The acute/subacute phase of herpes zoster was estimated to result in an average of 1.7 (standard error [SE] 0.02) additional physician and hospital outpatient visits, 0.05 (SE 0.003) additional emergency room visits, 0.03 (SE 0.003) additional inpatient hospital admissions, 2.1 (SE 0.03) additional prescriptions filled and $US431 (SE 17.60) in additional healthcare costs per patient. Among patients with acute/subacute herpes zoster, 21.1% had a diagnosis code with a designation for a herpes zoster-related complication, and 9.4% had three or more outpatient visits with a diagnosis code for herpes zoster. The average estimated incremental costs per patient with acute/subacute disease increased with age, ranging from $US258 (SE 37.70) among patients aged < or =19 years to $US805 (SE 106.30) among those aged > or =80 years. The numbers of additional outpatient visits, inpatient admissions, prescriptions filled for pain medications and coded complications were also substantially higher among older than younger patients with acute/subacute herpes zoster.

CONCLUSIONS

The management of acute/subacute herpes zoster was found to result in substantial healthcare costs, with outpatient care and prescription drugs comprising the majority of the cost burden. To more fully understand the overall cost of herpes zoster disease to society, future studies should examine the healthcare costs associated with post-herpetic neuralgia and productivity losses due to herpes zoster and post-herpetic neuralgia.

Natural history of pain following herpes zoster

In a longitudinal observational study of 94 patients (39 M:55 F, mean age 69) at elevated risk for developing post herpetic neuralgia (PHN), the natural history of pain during the first 6 months after herpes zoster (HZ) rash onset was determined. Pain severity and impact were rated using pain-VAS, SF-MPQ, and MPI. Applying a definition of PHN of average daily pain >0/100 on the pain VAS during the last 48 h, 30 subjects had PHN at 6 months. These 30 subjects reported more pain and a higher SF-MPQ score (p<0.01) at study inclusion than the 64 subjects whose pain completely resolved by 6 months. At 6 months, mean daily pain in the PHN group was 11/100 (95% CI 5,16) and only nine of these subjects were still taking prescription medication for HZ pain. The rate of recovery (pain severity over time) was the same in the PHN and no-pain groups. At study inclusion, the SF-MPQ and MPI scores in our PHN group were similar to historical controls with chronic severe PHN enrolled in clinical trials, but by 6 months the scores in our PHN subjects were significantly lower than historic controls. Only two subjects met the more stringent criteria for 'clinically meaningful' PHN at 6 months (> or = 30/100 on the pain VAS). Defining PHN as average daily pain >0/100 at 6 months after rash onset appears to substantially overestimate the number of HZ patients negatively impacted by ongoing pain and disability.

Repetitive paravertebral nerve block using a catheter technique for pain relief in post-herpetic neuralgia

We described in this report a case of post-herpetic neuralgia refractory to medical therapy that was successfully treated with repetitive injections of local aesthetic mixture (bupivacaine 0.5% 19 ml and clonidine 150 microg ml(-1) 1 ml) every 48 h for 3 weeks using a paravertebral catheter inserted at T2-T3 level.

The incidence of herpes zoster in a United States administrative database

BACKGROUND

Few recent studies have reported data on the incidence of herpes zoster (HZ) in U.S. general clinical practice.

OBJECTIVE

To estimate the age- and sex-specific incidence of HZ among U.S. health plan enrollees.

DESIGN

Data for the years 2000 to 2001 were obtained from the Medstat MarketScan database, containing health insurance enrollment and claims data from over 4 million U.S. individuals. Incident HZ cases were identified through HZ diagnosis codes on health care claims. The burden of HZ among high-risk individuals with recent care for cancer, HIV, or transplantation was examined in sub-analyses. Overall incidence rates were age- and sex-adjusted to the 2000 U.S. population.

PARTICIPANTS

MarketScan U.S. health plan enrollees of all ages.

MEASUREMENTS AND MAIN RESULTS

We identified 9,152 incident cases of HZ (3.2 per 1,000 person-years) (95% confidence interval [CI], 3.1 to 3.2 per 1,000). Annual HZ rates per 1,000 person-years were higher among females (3.8) than males (2.6) (P<.0001). HZ rates rose sharply with age, and were highest among individuals over age 80 (10.9 per 1,000 person-years) (95% CI, 10.2 to 11.6). The incidence of HZ per 1,000 person-years among patients with evidence of recent care for transplantation, HIV infection, or cancer (10.3) was greater than for individuals without recent care for these conditions (3.0) (P<.0001).

CONCLUSIONS

The overall incidence of HZ reported in the present study was found to be similar to rates observed in U.S. analyses conducted 10 to 20 years earlier, after age- and sex-standardizing estimates from all studies to the 2000 U.S. population. The higher rate of HZ in females compared with males contrasts with prior U.S. studies.

Pain and sensory dysfunction 6 to 12 months after inguinal herniotomy

Inguinal hernia repair is associated with a 5%-30% incidence of chronic pain, but the pathogenesis remains unknown. We therefore evaluated pain and sensory dysfunction by quantitative sensory testing 6-12 mo after open hemiorrhaphy. Before sensory testing, all patients (n = 72) completed a short-form McGill Pain Questionnaire and a functional impairment questionnaire. Sensory dysfunction in the incisional area was evaluated by quantification of thermal and mechanical thresholds, by mechanical pain responses (von Frey/pressure algometry), and by areas of pinprick hypoesthesia and tactile allodynia. The incidence of chronic pain was 28% (20 of 72). Quantitative sensory testing and pressure algometry did not demonstrate differences between the pain and nonpain groups, except for a small but significant increase in pain response to von Frey hair and brush stimulation in the pain group. Hypoesthesia, or tactile allodynia, in the incisional area was observed in 51% (37 of 72) of the patients, but the incidence did not differ significantly between the pain group and the nonpain group (14 of 20 versus 23 of 52; P > 0.3). We concluded that cutaneous hypoesthesia, or tactile allodynia, is common after inguinal hemiotomy but has a low specificity for chronic postherniotomy pain. Factors other than nerve damage may be involved in the development of chronic posthemiotomy pain.

Risk factors for postherpetic neuralgia in patients with herpes zoster

OBJECTIVES

To identify risk factors for postherpetic neuralgia (PHN) using a validated definition of this chronic neuropathic pain syndrome, to determine combinations of risk factors that identify patients with a high risk of developing PHN, and to examine the characteristics of patients with subacute herpetic neuralgia, that is, pain that persists beyond the acute phase of herpes zoster but that resolves before PHN can be diagnosed.

METHODS

The authors examined baseline and follow-up data from 965 herpes zoster patients enrolled within 72 hours of rash onset in two clinical trials of famciclovir.

RESULTS

Univariate and multivariate analyses indicated that older age, female sex, presence of a prodrome, greater rash severity, and greater acute pain severity made independent contributions to identifying which patients developed PHN. Patients with subacute herpetic neuralgia who did not develop PHN were significantly younger and had less severe acute pain than PHN patients but were significantly more likely to have severe and widespread rash than patients without persisting pain.

CONCLUSIONS

The independent contributions to the prediction of PHN made by older age, female sex, presence of a prodrome, greater rash severity, and greater acute pain severity suggest that these risk factors reflect different mechanisms that each contribute to the development of PHN. Subacute herpetic neuralgia that does not progress to PHN may reflect peripheral tissue damage and inflammation caused by a particularly severe or widespread rash.

Factors influencing the features of postherpetic neuralgia and outcome when treated with tricyclics

This paper retrospectively reviews features of postherpetic neuralgia (PHN) in up to 279 personal patients in relation to treatment outcome when treated with tricyclic antidepressants (TCAs). Factors affecting characteristics of PHN: (i) Patients with allodynia (89%) and/or burning pain (56%) have a much higher visual analogue pain intensity score than those without; (ii) Acyclovir (ACV) given for acute shingles (HZ) does not reduce the incidence of subsequent PHN, but reduces the pain intensity in PHN patients with allodynia; (iii) ACV given for acute HZ reduces the incidence of burning pain in subsequent PHN, but not of allodynia; (iv) ACV given for acute HZ reduces the incidence of clinically detectable sensory deficit in subsequent PHN. Factors affecting outcome of TCA-treated PHN: (i) The point in time at which TCA treatment is commenced is by far the most critical factor: started between 3 and 12 months after acute HZ onset, more than two-thirds obtain pain relief (NNT=1.8); between 13 and 24 months, two-fifths (41%) (NNT=3.6); and more than two years, one-third (NNT=8.3). Background and paroxysmal pain disappear earlier and are more susceptible of relief than allodynia. (ii) Twice as many (86%) of PHN patients without allodynia obtain pain relief with TCA treatment than those with (42%); (iii) the use of ACV for acute HZ more than halves the time-to-relief of PHN patients by TCAs; (iv) PHN patients with burning pain are significantly less likely to obtain pain relief with TCAs than those without (p<0.0001).

Laser-evoked potentials in post-herpetic neuralgia

OBJECTIVE

We evaluated the reliability of laser-evoked potentials (LEPs) as a diagnostic tool in patients with post-herpetic neuralgia (PHN), i.e. a chronic painful condition that causes small-diameter fibre dysfunction. Furthermore, we sought information on pathophysiology of PHN pain.

METHODS

We recorded 'late' LEPs after stimulation of the supraorbital, upper cervical, lower cervical, upper thoracic, mid thoracic, and lower thoracic territories in 12 control subjects and 40 patients with PHN. We also determined the correlation of LEP data with age, duration of disease, and severity and quality of pain.

RESULTS

At all stimulation sites, laser pulses invariably evoked high-amplitude brain potentials related to small-myelinated (A-delta) fibre activation. The laser perceptive threshold and LEP latency correlated with the distance of the dermatome from the brain (P<0.001). In patients, the perceptive threshold was higher and the LEP amplitude was lower in the affected dermatome than on the contralateral side (P<0.001). We found no significant LEP-clinical correlation except for a correlation between LEP abnormality and age.

CONCLUSIONS

Being sensitive and reliable in assessing sensory function also in proximal dermatomes, LEPs are a promising diagnostic tool in radiculopathies. Although PHN severely impairs small myelinated fibres, the lack of a significant correlation between LEP abnormalities and pain suggests that pain in PHN does not chiefly arise from a dysfunction of small-myelinated afferents.

The use of gabapentin for the treatment of postherpetic neuralgia

BACKGROUND

Varicella-zoster virus causes chickenpox and can reemerge later in life to cause herpes zoster or shingles. One of the most common and disabling complications of herpes zoster is postherpetic neuralgia (PHN).

OBJECTIVES

This article reviews the current primary literature about the efficacy and tolerability of gabapentin for the treatment of PHN. Gabapentin pharmacokinetics and drug interactions are also reviewed.

METHODS

A literature search in the English language was conducted using OVID Web, which contained the following databases: MEDLINE (1966-present), EMBASE (1980-2002), Current Contents/Clinical Medicine (1999-2002), Cochrane Controlled Trials Register (1898-present), Cochrane Database of Systemic Reviews (fourth quarter, 2002), and International Pharmaceutical Abstracts (1970-2002). Search terms used were postherpetic neuralgia; zoster; gabapentin; neuropathic pain; pain; pharmacoeconomic; cost; controlled clinical trial; randomized, controlled trial; postherpetic neuralgia and gabapentin; gabapentin and pain; treatment and postherpetic neuralgia; gabapentin and age; gabapentin and gender; gabapentin and ethnicity; and gabapentin and pharmacokinetics.

RESULTS

Gabapentin displays nonlinear absorption kinetics, is minimally protein bound (< 3%), has a high mean (SD) volume of distribution (50.4 [8.0] L), and is excreted via the kidneys as unchanged drug. Two randomized, placebo-controlled, parallel-group, multicenter clinical trials demonstrated the effectiveness of gabapentin at doses of up to 3600 mg/d to significantly reduce pain (P < 0.01 and P < 0.001), improve sleep (P < 0.01), and improve some parameters on the Short Form-McGill Pain Questionnaire (P < 0.05). Dizziness and somnolence were the most common side effects leading to withdrawal from the trials. The recommended dosage in adults is 300 mg at bedtime on day 1,300 mg BID on day 2, and 300 mg TID on day 3, titrating up as needed to 2400 to 3600 mg/d. To reduce adverse events in patients with renal impairment, the dose should be adjusted based on the patient's creatinine clearance.

CONCLUSIONS

Gabapentin appears to be effective and well tolerated for the short-term treatment of PHN. However, future controlled studies are needed to determine whether the effectiveness of gabapentin for PHN is maintained for > 2 months, to establish the optimal dose of gabapentin for PHN, and to compare the efficacy of gabapentin with that of other pharmacologic agents used for the treatment of PHN.

Capsaicin-sensitive primary afferents mediate responses to cold in rats with a peripheral mononeuropathy

Persistent sensitivity to noxious and innocuous somatic stimuli results from peripheral nerve injury. Following chronic constriction injury (CCI) of the sciatic nerve in the rat, the hind paw ipsilateral to the injury displays significantly decreased response latencies to a noxious heat stimulus (thermal hyperalgesia), compared with the contralateral uninjured paw. The ligated paw also shows increased lifting and duration of lifting from a cooled (4 +/- 1 degrees C) surface. To characterize the peripheral nerve component of increased sensitivity to cold, CCI rats were systemically injected with the potent capsaicin analog resiniferatoxin (RTX). Twenty-four hours following RTX injection response latencies to noxious heat were significantly increased for both the ligated and unligated hind paws. In addition, increased responsiveness of the ligated paw to the cold surface was significantly attenuated. The results demonstrate that the enhanced responsiveness to cold and heat following a CCI are mediated in part by RTX-sensitive primary afferents.