Trigeminal Postherpetic Neuralgia: From Pathophysiology to Treatment

PURPOSE OF REVIEW

Trigeminal postherpetic neuralgia (TG-PHN) is a neuropathic pain condition complicating herpes zoster (HZ) attributed to the trigeminal nerve. It poses significant challenges due to its persistent and debilitating nature. This review explores the clinical characteristics of TG-PHN, analyzes its pathophysiological underpinnings, and addresses existent and potential therapies.

RECENT FINDINGS

TG-PHN is one of the most common and complex PHN locations. It has distinguishing clinical and pathophysiological characteristics, starting with viral triggered injuries to the trigeminal ganglion (TG) and peripheral tissue and involving the ascending and descending brain modulation pathways. Current therapies include vaccines, oral and topical medications, and interventional approaches, like nerve blocks and neurostimulation. This review covers TG-PHN's clinical and physiological components, treatment options, and potential future targets for improved management. By exploring the complexities of this condition, we aim to contribute to developing more effective and targeted therapies for patients suffering from trigeminal PHN.

Current scenario and future applicability of antivirals against herpes zoster

Herpes zoster (HZ) is a common disease in the aging population and immunocompromised individuals, with a lifetime risk of 20%-30% that increases with age. HZ is caused by reactivation of the varicella-zoster virus (VZV), which remains latent in the spinal dorsal root ganglia and cranial sensory ganglia after resolution of the primary VZV infection. The main focus of HZ management is rapid recovery from VZV infection as well as the reduction and prevention of zoster-associated pain (ZAP) and postherpetic neuralgia (PHN). The use of antivirals against VZV is essential in the treatment of HZ. However, limited antivirals are only licensed clinically for the treatment of HZ, including acyclovir, valacyclovir, famciclovir, brivudine, and amenamevir. Fortunately, some new antivirals against different types of Herpesviridae have been investigated and suggested as novel drugs against VZV. Therefore, this review focuses on discussing the difference in efficacy and safety in the currently licensed antivirals for the treatment of HZ, the applicability of future novel antivirals against VZV, and the preventive or therapeutic effects of these antivirals on ZAP or PHN.

Subgrouping of Peripheral Neuropathic Pain Patients According to Sensory Symptom Profile Using the Korean Version of the PainDETECT Questionnaire

BACKGROUND

A culturally validated Korean version of the PainDETECT Questionnaire (PD-Q) was used to identify neuropathic pain components (NeP) in patients suffering from chronic pain. The purpose of this study was to determine if the Korean PD-Q can be used to subgroup patients with peripheral NeP according to sensory symptom profiles.

METHODS

This study included 400 Korean patients with peripheral neuropathic pain diagnosed as probable or definite NeP. The total scores and subscores for each item in PD-Q were transformed into a Z-score for standardization. Hierarchical cluster analysis was performed to identify clusters of subjects by PD-Q scores.

RESULTS

The mean total PD-Q score of the study participants was 14.57 ± 6.46. A hierarchical cluster analysis identified 5 clusters with distinct pain characteristic profiles. Cluster 1 had relatively severe burning and tingling sensations. The mean total PD-Q score for cluster 2 was the lowest of the 5 clusters. Cluster 3 tended to be vulnerable to pain in response to cold/heat stimulation. Cluster 4 showed relatively severe pain induced by physical stimuli, such as light touch or slight pressure. Cluster 5 had high scores for all NeP symptoms.

CONCLUSION

This study demonstrates the ability of patients to cluster by symptoms using the Korean PD-Q. Subgrouping of peripheral neuropathic pain by sensory symptom profile may be useful in making effective drug treatment decisions.

Evaluation of the efficacy of unipolar and bipolar spinal dorsal root ganglion radiofrequency thermocoagulation in the treatment of postherpetic neuralgia

Background

Different views have been proposed on the radiofrequency treatment modes and parameters of radiofrequency thermocoagulation of the spinal dorsal root ganglion for the treatment of postherpetic neuralgia (PHN). It is urgent to identify a more effective therapy for patients with PHN.

Methods

Patients who underwent radiofrequency thermocoagulation therapy for PHN were retrospectively reviewed and were divided into a radiofrequency thermocoagulation (CRF) and double neddles radiofrequency thermocoagulation (DCRF). The pain scores (numerical rating scale, NRS) were evaluated at the following time points before the operation, 1 day, 3 months, 6 months, 1 year, and 2 years after operation. The incidence of complications and the degree of pain relief were evaluated. The in vitro ovalbumin experiment was used to indicate the effects of radiofrequency thermocoagulation.

Results

Compared with the preoperative NRS scores, the postoperative NRS scores decreased significantly; the NRS scores of the DCRF group was lower than that of the CRF group at all time points from 6 months to 2 years following the operation. The total effective rate of the DCRF group was significantly higher than that of the CRF group at 2 years following the operation. The incidence of numbness in the DCRF group was higher than that noted in the CRF group. The ovalbumin experiments in vitro indicated that the effects of radiofrequency thermocoagulation were optimal when the distance between the two needles was 5 mm.

Conclusions

DCRF with a 5 mm spacing exhibits a longer duration and higher effective rate in the treatment of PHN and is worth promoting.

Pharmacological and non-pharmacological strategies for preventing postherpetic neuralgia: a systematic review and network meta-analysis

Background

Postherpetic neuralgia (PHN) is a refractory complication of herpes zoster (HZ). To prevent PHN, various strategies have been aggressively adopted. However, the efficacy of these strategies remains controversial. Therefore, we aimed to estimate the relative efficacy of various strategies used in clinical practice for preventing PHN using a network meta-analysis (NMA).

Methods

We performed a systematic and comprehensive search to identify all randomized controlled trials. The primary outcome was the incidence of PHN at 3 months after acute HZ. We performed both frequentist and Bayesian NMA and used the surface under the cumulative ranking curve (SUCRA) values to rank the interventions evaluated.

Results

In total, 39 studies were included in the systematic review and NMA. According to the SUCRA value, the incidence of PHN was lower in the order of continuous epidural block with local anesthetics and steroids (EPI-LSE), antiviral agents with subcutaneous injection of local anesthetics and steroids (AV + sLS), antiviral agents with intracutaenous injection of local anesthetics and steroids (AV + iLS) at 3 months after acute HZ. EPI-LSE, AV + sLS and AV + iLS were also effective in preventing PHN at 1 month after acute HZ. And paravertebral block combined with antiviral and antiepileptic agents was effective in preventing PHN at 1, 3, and 6 months.

Conclusions

The continuous epidural block with local anesthetics and steroid, antiviral agents with intracutaneous or subcutaneous injection of local anesthetics and a steroid, and paravertebral block combined with antiviral and antiepileptic agents are effective in preventing PHN.

Immunological mechanism of postherpetic neuralgia and effect of pregabalin treatment on the mechanism: a prospective single-arm observational study

BACKGROUND

Although neuropathic pain is a severe and common pain, its pathophysiology has not been elucidated yet. Studies in recent years have focused on the immune system's role in the pathogenesis of neuropathic pain. The aim of this study was to investigate the role of immunological mechanisms in neuropathic pain and the effect of pregabalin by measuring immunological marker levels in peripheral blood before and after pregabalin treatment in postherpetic neuralgia (PHN) patients with neuropathic pain.

METHODS

Forty patients diagnosed with PHN were included in the study. CD4, T follicular cells (Tfh: CD4+CXCR5+PD1+), Th17 (CD4+CCR6+ and CD4+IL17A+), regulatory T cells (Treg: CD4+ CD25+foxp3+), Th1 (CD4+ CXCR3+ and CD4+ IFN-γ+) and Th2 (CD4+ IL-4+) cell ratios were measured in peripheral blood samples before treatment and after 3 months of treatment.

RESULTS

When immunological marker and inflammation parameter levels were compared before and after treatment, the helper T cell ratio (CD3+, CD4+) was 30.28 ± 12.27% before treatment and 34.93 ± 11.70% after treatment, so there was a statistically significant increase (P = 0.028). Th17 was 4.75 ± 5.02% before treatment and 5.80 ± 3.13% after treatment, and there was a statistically significant increase (P = 0.036).

CONCLUSIONS

Immunological mechanisms play an essential role in the pathogenesis of neuropathic pain, immunologically based treatment approach will be the critical point of treatment.

Effectiveness of CT-guided epidural infiltration of steroids and local anesthetics for acute and chronic herpes zoster neuralgia

PURPOSE

The purpose of this study was to evaluate the effectiveness and complication rate of computed tomography (CT)-guided epidural injection of steroids and local anesthetics for pain relief in patients with neuralgia due to acute or chronic herpes zoster (HZ).

MATERIALS AND METHODS

A prospective study was conducted from April 2017 to February 2019 including patients with HZ neuralgia (HZN) at any stage (acute or chronic, the latter being defined as pain lasting more than 3 months and also called post herpetic neuralgia [PHN]). The sensory ganglion of the affected dermatome and/or the affected sensory nerve was targeted under CT-guidance and local injection of a mixture of two vials of methylprednisolone 40mg/mL and 2mL of Lidocaine 1% was performed. Using a visual analogue scale (VAS, 0 to 10), pain was assessed prior to the procedure, and at day 7, 1 month, 3 months and 6 months. Adverse effects were graded according to the Society of Interventional Radiology classification.

RESULTS

Twenty patients were included. There were 9 men and 11 women with a mean age of 67±13.9 (SD) years (range: 27-83 years). Of these, 14 patients had acute HZN and 6 had PHN. Mean VAS at baseline was 8.1±1.2 (SD) (range: 6-10) with significant decrease (P<0.0001) at day 7 (3.4±3.2 [SD]; range: 0-10), day 30 (3.4±3.2 [SD]; range: 0-9), day 90 (2.9±3.2 [SD]; range: 0-9), and day 180 (2.5±3.1 [SD]; range: 0-9). Infiltrations were significantly more effective on acute HZN than on PHN (P<0.001) and required significantly fewer infiltrations for pain relef (P=0.002). Only one grade A adverse event was reported.

CONCLUSION

Epidural injection of a mixture of steroids and local anesthetics under CT-guidance is effective on HZN with a persisting effect over 6 months.

Recombinant zoster vaccine (Shingrix®): a new option for the prevention of herpes zoster and postherpetic neuralgia

Postherpetic neuralgia (PHN) is a challenging condition for pain management specialists. The prevention of herpes zoster (HZ) and subsequent PHN in individuals aged 50 years and older, via the development of new vaccines, is an ongoing research project. The live zoster vaccine (LZV, Zostavax^®) was the first proof of concept that vaccination could prevent HZ, but LZV cannot be used in various immune-compromised patients. This led to the development of a new non-live recombinant zoster vaccine (RZV, Shingrix^®). This RZV has shown promising results in many clinical trials, with high reactogenicity and similar systemic adverse effects compared to those of LZV. The National Advisory Committee on Immunization has recommended LZV as a standard vaccine for HZ prevention in adults ≥ 50 years of age, but no studies directly comparing the safety and efficacy of RZV and LZV vaccines have been conducted. This article reviews the brief history, efficacy, and safety of the two vaccines and discusses the advantage of RZV over LZV based on the available literature.

Zoster sine herpete: a review

Zoster sine herpete (ZSH) is one of the atypical clinical manifestations of herpes zoster (HZ), which stems from infection and reactivation of the varicella-zoster virus (VZV) in the cranial nerve, spinal nerve, viscera, or autonomic nerve. Patients with ZSH display variable symptoms, such as neuralgia, however, different from HZ, ZSH show no zoster, which makes clinical diagnosis difficult. ZSH not only causes initial symptoms, such as neuropathic pain in the affected nerve, Bell palsy, and Ramsay Hunt syndrome, but also postherpetic neuralgia and fatal complications such as VZV encephalitis and stroke. The misdiagnosis of ZSH and tardy antiviral treatment may lead to severe ZSH sequelae. We review the publications related to ZSH, especially its diagnosis with VZV DNA and/or anti-VZV immunoglobulin (IgG and IgM). More work about ZSH, especially ZSH epidemiological survey and guidelines for its diagnosis and treatment, are needed because most of the present studies are case reports.

The efficacy of selective nerve root block for the long-term outcome of postherpetic neuralgia

Background

Several nerve blocks can reduce the incidence of postherpetic neuralgia (PHN) as well as relieve acute zoster-related pain, but the long-term outcome of PHN has not been clearly determined. This study investigated the efficacy of selective nerve root block (SNRB) for herpes zoster (HZ) on the long-term outcome of PHN.

Methods

We prospectively conducted an interview of patients who had undergone an SNRB for HZ from January 2006 to December 2016 to evaluate their long-term PHN status. The relationship between the time from HZ onset to the first SNRB and the long-term outcome of PHN was investigated.

Results

The data of 67 patients were collected. The patients were allocated to acute (SNRB ≤ 14 days, n = 16) or subacute (SNRB > 14 days, n = 51) groups. The proportions of cured patients were 62.5% and 25.5% in the acute and subacute groups (P = 0.007), respectively. In logistic regression, an SNRB >14 days was the significant predictor of PHN (adjusted odd ratio, 3.89; 95% confidence interval, 1.02-14.93; P = 0.047). Kaplan-Meier analysis revealed that time from the SNRB to the cure of PHN was significantly shorter in the acute group (2.4 ± 0.7 yr) than in the subacute group (5.0 ± 0.4 yr; P = 0.003).

Conclusions

An early SNRB during the acute stage of HZ (within 14 days) appears to decrease the incidence and shorten the duration of PHN, with a median of 5.0 years of follow-up.

Botulinum Toxin A Might Be an Alternative or Adjunct Therapy for the Treatment of Trigeminal and Postherpetic Neuralgia

ARTICLE TITLE AND BIBLIOGRAPHIC INFORMATION

The efficacy of botulinum toxin for the treatment of trigeminal and postherpetic neuralgia: A systematic review with meta-analyses. Shackleton T, Ram S, Black M, Ryder J, Clark GT, Enciso R. Oral Surg Oral Med Oral Pathol Oral Radiol 2016;122(1):61-71.

SOURCE OF FUNDING

Information not available TYPE OF STUDY/DESIGN: Systematic review and meta-analysis.

Prevalence and healthcare utilization of herpes zoster and postherpetic neuralgia in South Korea: disparity among patients with different immune statuses

OBJECTIVES

Despite the clinical and epidemiological importance of herpes zoster (HZ) and postherpetic neuralgia (PHN), their disease and economic burden related to immune status has not been studied in South Korea. Our aim was to calculate the prevalence and rate of healthcare utilization related to HZ and PHN among Korean patients stratified by immune status.

METHODS

This retrospective study used the Health Insurance Review and Assessment Service National Patients Sample (HIRA K-NPS) database, which includes all medical claims from January to December 2009 on a representative sample of the Korean population. HZ and PHN patients aged ≥ 50 years were categorized into three groups by immune status: severely immunocompromised group, moderately compromised group, and non-compromised group. The prevalence, disease-related healthcare utilization, and medical costs were compared across the three groups.

RESULTS

We estimated that there were 312,136 HZ patients and 48,461 PHN patients ≥ 50 years in South Korea. The prevalence of HZ and PHN was 18.54 and 2.88 per 1,000 persons, respectively, and increased with deteriorating immune status. The number of outpatient visits and hospitalization rate among HZ patients were highest in the severely immunocompromised group (4.38% and 7.52%, respectively) and lowest in the non-compromised group (3.82% and 4.08%, respectively). The average medical cost per patient in the severe group was the highest (240 US dollars) and that of the non-compromised group was the lowest (161 US dollars). No parameters were significantly different among patients with PHN by immunity.

CONCLUSIONS

HZ patients with severe immunodeficiency had a higher prevalence of HZ, more outpatient visits and hospitalizations, longer hospitalizations, and higher medical costs than their counterparts did. Efforts should be made to reduce the HZ-related burden of severely immunocompromised patients.

A population based study of the epidemiology of Herpes Zoster and its complications

OBJECTIVES

To assess the incidence of Herpes Zoster (HZ) and its complications in the Israeli general population and specifically in immune-compromised individuals, and to identify risk factors for developing HZ and post-herpetic neuralgia (PHN).

METHODS

A retrospective database search for newly diagnosed cases of HZ and of PHN during 2006-2010 was conducted using the comprehensive longitudinal database of Maccabi Health Services. Cox-proportional hazards models were used to assess associations between risk factors and HZ and PHN.

RESULTS

During 2006-2010 there were 28,977 newly diagnosed cases of HZ and 1508 newly diagnosed cases of PHN. Incidence density rate of HZ was 3.46 per 1000 person-years in the total population and 12.8 per 1000 person-years in immune-compromised patients. HZ and PHN incidence increased sharply with age. 12.4% and 3.1% of elderly HZ patients (≥ 65 years) developed PHN or ophthalmic complications, respectively. In multivariable analyses, HZ and PHN were associated with female sex, higher socioeconomic status, diabetes mellitus, cancer history, and HIV treatment.

CONCLUSIONS

Extrapolating to the entire Israeli population, we estimate over 24,000 new cases of HZ and 1250 new cases of PHN each year. Cost-effectiveness analysis should be performed to determine the threshold age for vaccination against HZ.