Is postherpetic neuralgia more than one disorder?

Study on the related factors of post-herpetic neuralgia in hospitalized patients with herpes zoster in Sichuan Hospital of Traditional Chinese Medicine based on big data analysis

Although various factors were reported to be related to post-herpetic neuralgia (PHN), studies based on adequate and comprehensive data were absent. Data was extracted from cases of hospitalized patients with herpes zoster in dermatology department, Sichuan hospital of traditional Chinese medicine range from December, 2011 to February, 2018, and then cleaned to build prediction model with TREENET algorithms. Following evaluated the prediction model by ROC and confusion matrix, variables importance ranking and variables dependency analysis were performed, resulting in the importance ranking of factors for PHN and the dependency between factors and PHN. Based on strict inclusion and exclusion criteria, 1303 (571 PHN and 732 normal controls) cases and 2958 indicators were selected. Model evaluation showed high ROC value (training sample = 0.985, test samples = 0.752) and high accuracy value (70.27%), which indicated that the model was predictive. After variables importance ranking and variables dependency analysis, 62 variables in the model were associated with the occurrence of PHN. Our study identified 62 variables related to PHN and revealed that various variables were the important risk factors for PHN, including age, MCHC, sodium and UA.

Post-herpetic neuralgia - a review of current management and future directions

Post-herpetic neuralgia (PHN) is common and treatment is often suboptimal with less than half of patients achieving adequate 50% pain relief. As an area of unmet clinical need and as an archetype of neuropathic pain, it deserves the attention of clinicians and researchers. Areas covered: This review summarises the epidemiology, pathophysiology, risk factors and clinical features of varicella infection. It describes the current and possible future management strategies for preventing varicella infection and reactivation and for treating PHN. Expert opinion: A highly successful Varicella Zoster (VZV) vaccine has not been universally adopted due to fears that it may increase Herpes Zoster (HZ) incidence - and thus PHN - in older, unvaccinated generations. This is a controversial theory but advances in the efficacy of vaccines against HZ may allay these fears and encourage more widespread adoption of the VZV vaccine. Treatment of PHN, as for any neuropathic pain, must be multidisciplinary and multimodal. Advances in sensory phenotyping technology and genomics may allow more individualised treatment. Traditional research methodologies are ill-suited to assess the kind of complex interventions that are necessary to achieve better clinical outcomes in this challenging field.

WITHDRAWN: Topical lidocaine for the treatment of postherpetic neuralgia

Background

This is an update of the original Cochrane review published in Issue 2, 2007. The cause of postherpetic neuralgia is damage to peripheral neurons, dorsal root ganglia, and the dorsal horn of the spinal cord, secondary to herpes zoster infection (shingles). In postherpetic neuralgia, peripheral neurons discharge spontaneously and have lowered activation thresholds, and exhibit an exaggerated response to stimuli. Topical lidocaine dampens peripheral nociceptor sensitisation and central nervous system hyperexcitability, and may benefit patients with postherpetic neuralgia.

Objectives

To examine efficacy and safety of topical lidocaine in the treatment of postherpetic neuralgia.

Search methods

We searched the Cochrane Pain, Palliative and Supportive Care Group Trials Register, CENTRAL, MEDLINE, EMBASE, LILACS, SIGLE, Citation Index, the reference lists of all eligible trials, key textbooks, and previous systematic reviews. Last search conducted April 2011.

Selection criteria

Randomised or quasi‐randomised trials comparing topical applications of lidocaine in patients of all ages with postherpetic neuralgia (pain persisting at the site of shingles at least one month after the onset of the acute rash).

Data collection and analysis

Two review authors extracted data, and a third checked them.

Main results

In the original review three studies involving 182 topical lidocaine treated participants and 132 control participants were included. Two studies gave data on pain relief, and the remaining study provided data on secondary outcome measures. The largest study published as an abstract compared topical lidocaine patch to a placebo patch and accounted for 150 of the 314 participants (48%).

A meta‐analysis combining two studies identified a significant difference between topical lidocaine and control groups for the primary outcome measure: a mean improvement in pain relief according to a pain relief scale. Topical lidocaine relieved pain better than placebo (P = 0.003).

There was a statistical difference between the groups for the secondary outcome measure of mean VAS score reduction (P = 0.03), but this was only for a single small study. There were a similar number of adverse skin reactions in both treatment and placebo groups.

The highest recorded blood lidocaine concentration varied between 59 ng/ml and 431 ng/ml between studies. The latter figure is high and the authors of the study suggest that the sample had been contaminated during the assay procedure.

Authors' conclusions

Since the last version of this review in Issue 2, 2007 no new studies have been found and the results therefore remain the same. There is still insufficient evidence to recommend topical lidocaine as a first‐line agent in the treatment of postherpetic neuralgia with allodynia. Further research should be undertaken on the efficacy of topical lidocaine for other chronic neuropathic pain disorders, and also to compare different classes of drugs (e.g. topical anaesthetic applications versus anti‐epileptic drugs).

Topical lidocaine may benefit some patients on an individual basis though there is stronger evidence for the use of other drugs. Postherpetic neuralgia is a long‐lasting pain disorder that causes pain from stimuli that are not normally painful. Local anaesthetics (such as lidocaine) can reduce the sensation of pain that is transmitted through nerves, and allow pain relief in patients with postherpetic neuralgia. This review found three small studies involving 182 topical lidocaine treated participants and 132 control participants using lidocaine for patients with postherpetic neuralgia. Two studies provided data on pain relief amongst patients with postherpetic neuralgia, and they showed some improvement in pain when topical lidocaine was compared to a placebo. No comparison was made with other medications that are in current use for the treatment of postherpetic neuralgia. The side effects of topical lidocaine are very minimal, but include skin problems (such as irritation and redness). We are unable to recommend the use of topical lidocaine as a first‐line treatment for postherpetic neuralgia at this stage. Further studies are needed to compare topical lidocaine to other medications in the treatment of postherpetic neuralgia.

Post herpetic neuralgia

BACKGROUND

During the past decade, important advances have been made in understanding the epidemiology, pathogenesis, prevention and treatment of post herpetic neuralgia pain as well as treatment of other neuropathic pain conditions. PHN is accepted as a model for management and clinical trials of neuropathic pain of less clear etiologies. In palliative medicine, where the etiology of pain may be nociceptive, neuropathic, or mixed, it is frequently to the research on PHN that we turn in order to extrapolate the data to the patients at hand.

OBJECTIVE

To review and summarize what is known about epidemiology, pathogenesis, clinical features and prevention strategies for post herpetic neuralgia. Discuss the available including the most recent therapeutic options as regards to their mechanism of action, efficacy, safety and tolerability in an attempt to explain the rationale for their use.

CONCLUSION

A multidisciplinary and integrative approach has the best chance of success in the management of patients with PHN pain, a problem that can be often frustrating to the patient and challenging to the clinician. Prevention strategies for PHN include administration of zoster vaccine, treatment with antiviral therapy within 72 hours of rash onset and aggressive pain control. First and second line pharmacotherapy include anticonvulsants, antidepressants, topical lidocaine, high dose capsaicin, and opioids either used individually or in combination. Interventional techniques play a limited role in the management of PHN although some data indicate that Intrathecal methylprednisolone and spinal cord stimulation may be effective.

An adaptive procedure for routine measurement of light-touch sensitivity threshold

Quantitative sensory testing with Semmes-Weinstein monofilaments suffers from several pitfalls. Our aims were to assess the reliability of these filaments for touch-pressure threshold detection, develop and validate a rapid and accurate procedure for measurements at the bedside, and establish normative data. After calibration of the monofilaments, an adaptive staircase algorithm was validated and used to establish normative data in healthy subjects. Calibration showed significant differences between manufacturer- and investigator-produced data. The relative humidity significantly affected the force exerted by the filaments. The adaptive procedure showed good accuracy and substantial time-saving. Touch-pressure thresholds showed significant gender differences (mean +/- 2 SD for females/males: 2.82-12.3/3.09-17.78 g/mm(2)). The influence of body site and age is small. Accurate use of Semmes-Weinstein monofilaments requires prior calibration, correction for humidity, and use of a validated procedure. In this study we provide normative data that can be used with our algorithm.

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.

Mechanisms of pain and itch caused by herpes zoster (shingles)

Study of humans with shingles or postherpetic neuralgia (PHN) is providing insights into pain mechanisms. Shingles pain is a combination of normal and neuropathic pain that reflects acute tissue and neural injury. PHN pain, which lasts after tissues have healed, is caused by persistent neural injuries. Spontaneous C-nociceptor activity has been documented in painful polyneuropathies and probably occurs in shingles as well, although there are no microneurographic studies of either shingles or PHN. It is uncertain if this persists in PHN since pathological examination of PHN-affected nerves and ganglia show chronic neuronal loss and quiescent scarring without inflammation. Skin-biopsy study has correlated the presence of PHN with the severity of persistent distal nociceptive axon loss, and autopsy has correlated pain persistence with segmental atrophy of the spinal cord dorsal horn, highlighting the importance of central responses to nerve injury. Pathological studies of tissues from patients with trigeminal neuralgia suggest that brief lancinating pains reflect ephaptic neurotransmission between adjacent denuded axons. The mechanisms of chronic spontaneous pain and mechanical allodynia remain uncertain despite considerable indirect evidence from animal models. Postherpetic itch is presumably caused by unprovoked firing of the peripheral and/or central neurons that mediate itch. If it occurs in neurons innervating skin left severely deafferented from shingles ("numb"), patients can give themselves painless injuries from scratching. Further human study, by electrophysiological recording, by structural and functional imaging, and by autopsy, should continue to provide much-needed insights.

PERSPECTIVE

Many patients continue to have chronic pain and/or itch after shingles that is unrelieved by current treatments. Many will gladly volunteer for clinical studies, including autopsy, to try and improve understanding of these common and disabling conditions. Their prevalence makes highly powered studies feasible. Funding and organization are the current bottlenecks.

Facial altered sensation and sensory impairment after orthognathic surgery

The aim of this study was to determine whether impairment of sensory functions after trigeminal nerve injury differs in severity among patients who report qualitatively different altered sensations. Data were obtained from 184 patients. Before and at 1, 3 and 6 months after orthognathic surgery, patients were grouped as having no altered sensation, negative sensations only (hypoaesthetic), mixed sensations (negative+active), or active sensations only (paraesthetic or dysaesthetic). Bias-free estimates of contact detection and two-point discrimination were obtained to assess, via ANOVA, whether patients in the four groups exhibited different levels of sensory impairment. Impairment in contact detection and two-point discrimination was found to differ significantly among the groups at 6 months but not at 1 month. At 6 months, patients who reported negative sensations only exhibited the greatest impairment, on average, in contact detection; in contrast, patients who reported mixed sensations exhibited the greatest impairment in two-point discrimination. The least residual impairment at 6 months was observed in patients who reported no altered sensation. It is recommended that clinical judgments regarding nerve injury-associated sensory dysfunction should not be based on threshold testing results without consideration of patients' subjective reports of altered sensation.

Relief of post-herpetic neuralgia by surgical removal of painful skin: 5 years later

Surgical removal of painful skin was first attempted as a treatment for chronic intractable post-herpetic neuralgia (PHN) more than a century ago, but long-term follow-up has rarely been reported. A patient who underwent surgical excision of 294cm(2) of thoracic skin comprising the entire area of pain and allodynia in October 2000 has been followed for 5.5years post-surgery. Our initial report presented evidence of benefit in the form of reduced pain, elimination of allodynia, and reduced medication consumption during the first post-operative year. Unfortunately, pain steadily increased and now exceeds pre-surgery levels despite increased medication use. Pain topography and characteristics are different from pre-surgery and may relate to the pathophysiology of PHN. Skin resection cannot be recommended as a treatment for PHN.

Topical lidocaine for the treatment of postherpetic neuralgia

BACKGROUND

The cause of postherpetic neuralgia is damage to peripheral neurons, dorsal root ganglia, and the dorsal horn of the spinal cord, secondary to herpes zoster infection (shingles). In postherpetic neuralgia, peripheral neurons discharge spontaneously and have lowered activation thresholds, and exhibit an exaggerated response to stimuli. Topical lidocaine dampens peripheral nociceptor sensitisation and central nervous system hyperexcitability, and may benefit patients with postherpetic neuralgia.

OBJECTIVES

To examine the efficacy and safety of topical lidocaine in the treatment of postherpetic neuralgia.

SEARCH STRATEGY

We searched the Cochrane Pain, Palliative and Supportive Care Group Trials Register, The Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, and LILACS, SIGLE for conference proceedings, Citation Index, the reference lists of all eligible trials, key textbooks, and previous systematic reviews. We also wrote to authors of all identified trials.

SELECTION CRITERIA

Randomised or quasi-randomised trials comparing all topical applications of lidocaine, including gels and patches in patients of all ages with postherpetic neuralgia (pain persisting at the site of shingles at least one month after the onset of the acute rash).

DATA COLLECTION AND ANALYSIS

Two review authors extracted data, and a third checked them. We obtained some missing data from the US Food and Drugs Administration.

MAIN RESULTS

Three trials involving 182 topical lidocaine treated participants and 132 control participants were included. Two trials gave data on pain relief, and the remaining study provided data on secondary outcome measures. The largest trial published as an abstract compared topical lidocaine patch to a placebo patch and accounted for 150 of the 314 patients (48%).A meta-analysis combining two of the three studies identified a significant difference between the topical lidocaine and control groups for the primary outcome measure: a mean improvement in pain relief according to a pain relief scale. Topical lidocaine relieved pain better than placebo (P = 0.003). There was a statistical difference between the groups for the secondary outcome measure of mean VAS score reduction (P = 0.03), but this was only for a single small trial. There were a similar number of adverse skin reactions in both treatment and placebo groups. The highest recorded blood lidocaine concentration varied between 59 ng/ml and 431 ng/ml between trials. The latter figure is high and the authors of the study suggest that the sample had been contaminated during the assay procedure.

AUTHORS' CONCLUSIONS

There is insufficient evidence to recommend topical lidocaine as a first-line agent in the treatment of postherpetic neuralgia with allodynia. Further research should be undertaken on the efficacy of topical lidocaine for other chronic neuropathic pain disorders, and also to compare different classes of drugs (e.g. topical anaesthetics versus anti-epileptics).

Post-herpetic neuralgia in older adults: evidence-based approaches to clinical management

Many individuals across the globe have been exposed to the varicella-zoster virus (VZV) that causes chickenpox. After chickenpox has resolved, the virus remains latent in the dorsal root ganglia where it can re-emerge later in life as herpes zoster, otherwise known as shingles. Herpes zoster is a transient disease characterised by a dermatomal rash that is usually associated with significant pain. Post-herpetic neuralgia (PHN) is the term used for the condition that exists if the pain persists after the rash has resolved. Advanced age and compromised cell-mediated immunity are significant risk factors for reactivation of herpes zoster and the subsequent development of PHN. Though the pathophysiology of PHN is unclear, studies suggest peripheral and central demyelination as well as neuronal destruction are involved. Both the vaccine against VZV (Varivax) and the newly released vaccine against herpes zoster (Zostavax) may lead to substantial reductions in morbidity from herpes zoster and PHN. In addition, current evidence suggests that multiple medications are effective in reducing the pain associated with PHN. These include tricyclic antidepressants, antiepileptics, opioids, NMDA receptor antagonists as well as topical lidocaine (lignocaine) and capsaicin. Reasonable evidence supports the use of intrathecal corticosteroids, but the potential for neurological sequelae should prompt caution with their application. Epidural corticosteroids have not been shown to provide effective analgesia for PHN. Sympathetic blockade may assist in treating the pain of herpes zoster or PHN. For intractable PHN pain, practitioners have performed delicate surgeries and attempted novel therapies. Although such therapies may help reduce pain, they have been associated with disappointing results, with up to 50% of patients failing to receive acceptable pain relief. Hence, it is likely that the most effective future treatment for this disease will focus on prevention of VZV infection and immunisation against herpes zoster infection with a novel vaccine.

An Interdisciplinary Expert Consensus Statement on Assessment of Pain in Older Persons

This paper represents an expert-based consensus statement on pain assessment among older adults. It is intended to provide recommendations that will be useful for both researchers and clinicians. Contributors were identified based on literature prominence and with the aim of achieving a broad representation of disciplines. Recommendations are provided regarding the physical examination and the assessment of pain using self-report and observational methods (suitable for seniors with dementia). In addition, recommendations are provided regarding the assessment of the physical and emotional functioning of older adults experiencing pain. The literature underlying the consensus recommendations is reviewed. Multiple revisions led to final reviews of 2 complete drafts before consensus was reached.

The Potential of Treatment Matching for Subgroups of Patients With Chronic Pain

A large and diverse number of treatments have been shown to be effective in reducing pain and other symptoms for a minority but statistically significant number of patients in different chronic pain syndromes. The means by which such different treatments achieve similar outcomes is not well understood. In this paper, the importance of considering patient heterogeneity for those who may be diagnosed with the same medical syndrome is discussed. The author suggests that the lack of satisfactory treatment outcomes for the treatments of chronic pain syndromes may be accounted for by the patient homogeneity myth--the assumption that all patients with the same medical diagnosis are similar on all important variables. The importance of subdividing (splitting) patients into meaningful groups is described. Studies presenting data on the identification of patient subgroups based on psychosocial and behavioral characteristics and the reliability and validity of this approach are presented. Some initial attempts to demonstrate the potential for matching treatments to patient subgroups are described.

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.

Systematic Overview of the Pharmacological Management of Postherpetic Neuralgia

OBJECTIVE

This study systematically reviews current evidence on drug treatments commonly used in postherpetic neuralgia.

METHODS

Randomized controlled trials were critically selected using predefined search criteria. Efficacy was evaluated as percentage of improvement in pain intensity between baseline and endpoint, tolerability by number of study discontinuations because of adverse events and incidence of adverse events.

RESULTS

Currently published trials enrolled different patient populations and small patient numbers. The great variability in doses, titration schemes, designs and washout periods together with other design flaws made comparison between different studies scientifically impossible.

CONCLUSIONS

There is a real need for well-performed clinical trials with standardization in design and reporting. Development of adequate and validated questionnaires for evaluation and comparison of efficacy and safety of treatments is also needed. Based on the evaluation of individual studies, it is concluded that only gabapentin is studied in large (over 200 patients), placebo-controlled studies showing good efficacy and safety.

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).

Treatment and prevention of postherpetic neuralgia

There have been 4 recent major advances in the treatment of postherpetic neuralgia (PHN) that are based on the results of randomized, controlled trials. These advances are the demonstrations that gabapentin, the lidocaine patch 5%, and opioid analgesics are efficacious in patients with PHN, and the report that nortriptyline and amitriptyline provide equivalent analgesic benefits for patients with PHN but that nortriptyline is better tolerated. The results of these clinical trials are briefly reviewed, and their implications for the treatment of patients with PHN are discussed. Despite these treatment advances, many patients remain refractory to current therapy, and the prevention of PHN has therefore become an important focus of current research. Research on administration of the varicella-zoster vaccine to prevent herpes zoster and on treatment of patients who have herpes zoster with combined antiviral and analgesic therapy to prevent PHN is discussed.

An overview of neuropathic pain: syndromes, symptoms, signs, and several mechanisms

OBJECTIVE

An overview is presented of neuropathic pain syndromes, their characteristic symptoms and signs, and recent approaches to identifying their pathophysiologic mechanisms.

DESIGN

The results of recent clinical studies of neuropathic pain are reviewed. Chronic neuropathic pain syndromes are emphasized because these long-lasting and often disabling conditions present a much greater challenge for the clinician than acute pain. Peripheral neuropathic syndromes have received greater attention in the research literature than central pain, and studies of syndromes such as postherpetic neuralgia and painful diabetic neuropathy provide the basis for current knowledge of neuropathic pain.

CONCLUSIONS

Precise estimates of the prevalence of neuropathic pain are not available, but chronic neuropathic pain may be much more common than has generally been appreciated and its prevalence can be expected to increase in the future. There is considerable agreement that both peripheral and central processes contribute to many chronic neuropathic pain syndromes, and that these different mechanisms may explain the qualitatively different symptoms and signs that patients experience. The limitations of existing treatments for neuropathic pain and the inability to provide relief for many patients has stimulated ongoing studies that examine different approaches to preventing neuropathic pain.

Current management of postherpetic neuralgia

BACKGROUND

The herpes zoster rash occurs when a dormant varicella zoster virus reactivates in dorsal root and cranial nerve ganglia. Pain that persists in the region where this rash occurred after the cutaneous lesions have healed is termed postherpetic neuralgia (PHN). A wide variety of therapies has been used with varying degrees of success to prevent the occurrence of PHN and to reduce pain with established PHN.

REVIEW SUMMARY

In this review, we discuss the clinical presentation of PHN, current strategies for the prevention and management of this disease, and observations that have increased our understanding of the neural mechanisms involved in PHN.

CONCLUSIONS

Several classes of drugs are effective in attenuating the pain and hyperalgesia caused by PHN, but no single drug leads to the complete relief of symptoms. Additional research is needed to improve treatment strategies and define the role of invasive pain management techniques in cases where PHN is associated with intractable pain.

Relief of post-herpetic neuralgia by surgical removal of painful skin

We present a case of longstanding PHN treated by skin excision of the area of greatest pain (11.3 x 26.0 cm(2)). The operation reduced pain, eliminated tactile allodynia, and facilitated greatly reduced medication use over a 1-year follow-up period. Fourteen punch biopsies and 10 strips of skin (each 10 mm long) from the excised painful PHN skin were qualitatively assessed by double-label immunofluorescence using antibodies against protein-gene-product 9.5 (PGP9.5), 200 kDa neurofilament protein (NF), calcitonin gene-related peptide (CGRP) and vanilloid receptor-1 (VR-1). Compared with a punch biopsy from mirror image skin, the pattern of cutaneous innervation in PHN skin was consistently and substantially different. The results may explain the anatomical basis of the capsaicin-response test and have implications for our understanding of clinical mechanisms underlying PHN pain.

Neurogenic hyperalgesia versus painful hypoalgesia: two distinct mechanisms of neuropathic pain

Patients with sensory disturbances of painful and non-painful character show distinct changes in touch and/or pain sensitivity. The patterns of sensory changes were compared to those of human surrogate models of neuropathic pain to assess the underlying mechanisms. We investigated 30 consecutive in-patients with dysaesthesia of various origins (peripheral, spinal, and brainstem lesions) and 15 healthy subjects. Tactile thresholds were determined with calibrated von Frey hairs (1.1mm). Thresholds and stimulus-response functions for pricking pain were determined with a series of calibrated punctate mechanical stimulators (0.2mm). Allodynia was tested by light stroking with a brush, Q-tip, and cotton wisp. Perceptual wind-up was tested by trains of punctate stimuli at 0.2 or 1Hz. Intradermal injection of capsaicin (n=7) and A-fiber conduction blockade (n=8) served as human surrogate models for neurogenic hyperalgesia and partial nociceptive deafferentation, respectively. Patients without pain (18/30) showed a continuous distribution of threshold shifts in the dysaesthetic skin area with a low to moderate increase in pain threshold (by 1.52+/-0.45 log2 units). Patients with painful dysaesthesia presented as two separate groups (six patients each): one showing lowered pain thresholds (by -1.94+/-0.46 log2 units, hyperalgesia) and the other elevated pain thresholds (by 3.02+/-0.48 log2 units, hypoalgesia). The human surrogate model of neurogenic hyperalgesia revealed nearly identical leftward shifts in stimulus-response function for pricking pain as patients with spontaneous pain and hyperalgesia (by a factor of about 5 each). The sensory changes in the human surrogate model of deafferentation were similar to patients with hypoalgesia and spontaneous pain (rightward shift of the stimulus-response function with a decrease in slope). Perceptual wind-up did not differ between symptomatic and control areas. There was no exclusive association of any parameter obtained by quantitative sensory testing with a particular disease (of either peripheral or central origin). Our findings suggest that neuropathic pain is based on two distinct mechanisms: (I) central sensitization (neurogenic hyperalgesia; in patients with minor sensory impairment) and (II) partial nociceptive deafferentation (painful hypoalgesia; in patients with major sensory deficit). This distinction as previously postulated for postherpetic neuralgia, is obviously valid also for other conditions. Our findings emphasize the significance of a mechanism-based classification of neuropathic pain.

Symptom assessment and management

This article reviews how to assess and manage several symptoms commonly encountered by neurologists who care for patients with advanced illness. Scientifically validated guidelines are reviewed and practical advice is offered on how to manage pain, nausea and vomiting, dyspnea, and respiratory secretions at the end of life. The role of the neurologist as a provider of end of life care is discussed including suggestions for communicating with patients and families. This article concludes with a review of when sedation may be offered within the purview of good palliative care to patients who are imminently dying.

Acute pain in herpes zoster: the famciclovir database project

The results of a considerable number of recent prospective studies have demonstrated that greater acute pain severity in herpes zoster patients is associated with a significantly greater risk of developing postherpetic neuralgia (PHN). Only a few studies have examined the relationships between acute pain severity and demographic characteristics and clinical features of patients with herpes zoster, however, and the results of these studies have been inconsistent. To clarify these relationships, data from 1778 herpes zoster patients studied within 72 h of rash onset in four clinical trials of the antiviral agent famciclovir were examined. Univariate and multivariate analyses indicated that greater acute pain severity was significantly associated with greater age, female sex, greater rash severity, the presence of a prodrome, and primary involvement of non-trigeminal dermatomes. These results demonstrate that three of the established risk factors for PHN - older age, greater rash severity, and the presence of a prodrome - are also associated with more severe acute pain assessed soon after rash onset in patients with herpes zoster. The results of this study are consistent with the recommendation that herpes zoster patients who are older, who have had a prodrome, or who have severe rash or severe acute pain should be targeted for interventions designed to prevent PHN.

Capsaicin evoked pain and allodynia in post-herpetic neuralgia

The hypothesis that the pain and allodynia associated with post-herpetic neuralgia (PHN) is maintained by a combination of input from preserved primary afferent nociceptors and sensitization of central pain transmitting neurons was examined in 17 subjects with PHN. Pain, allodynia, thermal sensory function, cutaneous innervation, and response to controlled application of 0.075% capsaicin were measured. Compared to mirror-image skin, applying capsaicin on a 9 cm(2) area of PHN skin significantly increased overall PHN pain and allodynia in 11 of 17 subjects. These 'capsaicin responders' were characterized by higher average daily pain, higher allodynia ratings, and relatively preserved sensory function at baseline compared to the non-responders. In three of the 'capsaicin responders' the area of allodynia expanded into previously non-allodynic and non-painful skin that had normal sensory function and cutaneous innervation. These observations support the hypothesis that allodynia in some PHN patients is a form of chronic secondary hyperalgesia maintained by input from intact and possibly 'irritable' primary afferent nociceptors to a sensitized CNS.

The role of sympathetic nerve blocks in herpes zoster and postherpetic neuralgia

The most common complication of herpes zoster in immunocompetent patients is postherpetic neuralgia (PHN). Sympathetic blocks have been traditionally used for patients with herpes zoster and PHN with three different therapeutic goals: pain relief during acute herpes zoster, pain relief during PHN, and prevention of PHN by treating patients with acute zoster. The role of sympathetic blocks in herpes zoster and PHN remains controversial due to methodologic shortcomings in published studies and the limited current understanding of the role of the sympathetic nervous system in mediating pain. Current theories of the pathophysiology of PHN, the role of the sympathetic nervous system in herpes zoster and PHN, and published studies investigating use of sympathetic nerve blocks in herpes zoster and PHN are reviewed.

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

Sensory loss and allodynia are hallmark signs of postherpetic neuralgia (PHN). We set out to investigate how frequently these signs are present in patients with acute herpes zoster (HZ) and what their prognostic value might be. We assessed pain, mechanical allodynia, and sensitivity to pinprick in 113 immunocompetent patients with HZ of a median duration of 5 days. Follow-up visits took place at 2 weeks, 6 weeks, 3 months, and 6 months. When first seen, 87 (77%) patients reported ongoing pain and 48/107 (45%) had allodynia. Twenty-eight (25%) patients had pain at 3 months (and were considered to have developed PHN), while 14 (12%) patients had pain at 6 months. Allodynia tended to subside quickly in most patients. Reduced sensitivity to pinprick was less common. Mechanical allodynia and pinprick hypesthesia were strongly associated with the development of PHN. They merit addition to the list of potential risk factors for PHN although they cannot be used as a predictive rule for an individual patient. By contrast, lack of allodynia in the early stages of HZ predicts good recovery by three months.

Treatment of postherpetic neuralgia: an update

Postherpetic neuralgia (PHN) is a chronic pain syndrome that is often refractory to treatment and can last for years, causing physical and social disability, psychological distress, and increased use of the healthcare system. In this paper we provide an update on recent developments in the treatment of PHN. We emphasise the results of recent studies that provide an evidence-based approach for treating PHN that was not available until very recently. In randomised, controlled clinical trials, the topical lidocaine patch, gabapentin, and controlled release oxycodone have been shown to provide superior pain relief in patients with PHN when compared with placebo. It has also recently been demonstrated that the tricyclic antidepressant nortriptyline provides equivalent analgesic benefit when compared with amitriptyline, but is better tolerated. Based on these results, nortriptyline can now be considered the preferred antidepressant for the treatment of PHN, although desipramine may be used if the patient experiences unacceptable sedation from nortriptyline. The topical lidocaine patch, gabapentin and controlled release oxycodone all appear to be as effective as tricyclic antidepressants in the treatment of patients with PHN, and the results of these recent studies suggest that each of these treatments should be considered early in the course of treatment. Additional controlled trials are needed to compare the efficacy and tolerability of these 4 treatments- tricyclic antidepressants, gabapentin, the topical lidocaine patch and controlled release opioid analgesics--used singly and in various combinations in the treatment of patients with PHN.

Psychiatric symptoms and distress differ between patients with postherpetic neuralgia and peripheral vestibular disease

OBJECTIVE

No previous studies have investigated the psychiatric characteristics of patients with postherpetic neuralgia (PHN). Similarly, no studies have been performed on patients with different chronic somatic symptoms due to a defined medical disease to compare the characteristics of psychiatric morbidity associated with each etiology.

METHODS

After completing the subscales of the Symptom Checklist 90-R, a psychiatrist administered the Diagnostic Interview Schedule to all subjects. The psychiatric comorbidity in 35 patients with pain due to PHN was compared with a control group of 34 patients with the nonpainful aversive symptom of vertigo due to a peripheral vestibular disorder that caused unilateral hypofunction.

RESULTS

PHN patients had significantly more symptoms of major depression and somatization disorder. No significant differences were found between groups for psychiatric diagnoses. Patients with PHN reported significantly less acutely distressing somatic symptoms.

CONCLUSION

These results suggest that the psychiatric symptoms of patients with PHN are distinct from nonspecific acute distress and may be related to the experience of suffering from chronic neuropathic pain. Patients with PHN may not meet criteria for a psychiatric diagnosis, but their psychiatric comorbidity places them at substantial risk for increased pain, suicidal ideation, sustained disability, and the numerous complications of excessive medical evaluation and treatment. Patients with PHN should be evaluated specifically for psychiatric symptoms to reduce potential negative consequences through appropriate treatment.