Postherpetic neuralgia: epidemiology, pathophysiology, and pain management pharmacology

Modalities in managing postherpetic neuralgia

Postherpetic neuralgia (PHN) is the most troublesome side effect of Herpes Zoster (HZ), which mainly affects the elderly and immunocompromised populations. Despite the current advancement of treatments, PHN persists in many individuals influencing their daily activities and reducing their quality of life. Anticonvulsants, antidepressants, topical therapies including lidocaine and capsaicin, and opioids, are the most widely used therapies for the treatment of PHN. These medications come with their adverse effects, so they should be used carefully with the elderly or with patients with significant comorbidities. Other measures like botulinum toxin, nerve blocks, spinal cord stimulation, and radiofrequency have also contributed significantly to the management of PHN. However, the efficacy, safety, and tolerability of these invasive methods need to be carefully monitored when administering them. Early diagnosis and early initiation of treatment can reduce the burden associated with PHN. The zoster vaccine has effectively reduced the incidence of HZ and PHN. In this article, we discuss the treatment options available for the management of PHN, mainly focusing on the efficacy and safety of different therapeutic modalities.

The effect and safety of ozone autohemotherapy combined with pharmacological therapy in postherpetic neuralgia

Introduction

We investigated the effect and safety of ozone autohemotherapy combined with pharmacological therapy in postherpetic neuralgia (PHN).

Methods

Ninety-eight patients with PHN were enrolled in this study and randomly divided into a pharmacological therapy group and ozone autohemotherapy group (49 patients in each group). The PHN patients in the pharmacological therapy group were administered pharmacological therapy for 2 weeks, whereas PHN patients in the ozone autohemotherapy group were given ozone autohemotherapy (200 mL blood from patients, the concentration of medical ozone was set as 30 μg/mL using an ozone medical apparatus, 40 mL medical ozone was incubated in 200 mL autologous blood for 3–5 minutes) combined with pharmacological therapy for 2 weeks. The Visual Analog Scale (VAS), the 50% VAS reduction in the initial value, McGill Pain Questionnaire (MPQ), the Patients’ Global Impression of Change (PGIC) scale, and the World Health Organization Quality of Life (WHOQOL-BREF) instrument were used to evaluate the outcomes of all PHN patients before therapy and at 1 week, 1 month, and 3 months after therapy.

Results

Forty-five patients in the pharmacological therapy group and 47 patients in the ozone autohemotherapy group completed the study. Compared with before therapy, the two groups showed significant improvements in VAS, MPQ, PGIC, and WHOQOL-BREF scores after therapy (P<0.05). Moreover, compared with the scores of the pharmacological therapy group, the ozone autohemotherapy group’s scores were significantly improved in the VAS, MPQ, PGIC, and WHOQOL-BREF as well as the 50% VAS reduction of the initial value after therapy (P<0.05). Finally, there were no statistically significant differences in adverse effects between groups after therapy (P>0.05).

Conclusion

The results of this study demonstrated that ozone autohemotherapy combined with pharmacological therapy was superior to isolated pharmacological therapy in patients with PHN and was an effective and safe way to relieve PHN.

Development of adjuvanted recombinant zoster vaccine and its implications for shingles prevention

INTRODUCTION

GSK has developed a two-dose adjuvanted recombinant zoster vaccine (Shingrix, RZV) to protect people aged ≥50 years (50+) against herpes zoster (HZ) and its complications. RZV showed >90% efficacy against HZ, sustained over 4 years of follow-up, in all studied age groups.

AREAS COVERED

This article reviews the scientific rationale underlying the design of RZV; the clinical evidence demonstrating immunogenicity, safety, and efficacy in persons 50+; and the public health implications and cost-effectiveness.

EXPERT COMMENTARY

A decline in varicella zoster virus (VZV) immunity is associated with increased risk of HZ in adults 50+ and immunocompromised individuals. RZV was designed to restore levels of anti-VZV cellular and humoral immunity to prevent VZV reactivation. RZV includes the recombinant gE glycoprotein antigen, and Adjuvant System AS01_B which promotes cellular and antibody responses. In two Phase III studies in subjects aged 50+ and 70+ years, RZV efficacy against HZ compared to placebo was >90% and ≥89% against post-herpetic neuralgia (PHN). RZV is expected to dramatically impact HZ morbidity including its complications, and associated health-care costs. In the US population aged 50+ years, vaccination with RZV can be cost-effective compared to no vaccination and cost-saving compared to the currently available live-attenuated HZ vaccine (Zostavax, Merck).

Effects of gabapentin, pregabalin and gastroretentive gabapentin on simulated driving, daytime sedation and cognition

Aim: Randomized Phase I study examining the effects of gabapentinoids gabapentin, pregabalin and gastroretentive gabapentin on simulated driving performance, sedation and cognitive function in healthy volunteers (n = 32). Methods: Driving attentiveness, sleepiness and cognition were evaluated prior to subjects receiving study doses. Blood samples were collected during each treatment. Results: Subjects receiving gastroretentive gabapentin showed less change in variation in lateral lane position (p = 0.0275), less tremor (p = 0.0304) and fewer vision disturbances compared with gabapentin (p = 0.0177). Statistically significant decrease in One Card Learning Test performance was observed after treatment with gastroretentive gabapentin. Conclusion: Gastroretentive gabapentin demonstrated reduced driving impairment and lower scores on key neurotoxicity measures. Further studies in patients with postherpetic neuralgia are needed.

Clinical trial number: NCT03179345

Combined therapy of pulsed radiofrequency and nerve block in postherpetic neuralgia patients: a randomized clinical trial

Caused by viral infection, postherpetic neuralgia (PHN) is the most common chronic neuropathic pain. Various treatment modalities such as early use of nerve block therapy (NBT) and pulsed radiofrequency (PRF) have been studied in reducing pain, however, no consistent success was achieved in all the patients treated with single regimen. The combined therapy of PRF and NBT with different targeting mechanism are of interest and remains to be determined. Here we investigated the combined effects of pulsed radiofrequency (PRF) with nerve block therapy (NBT) in PHN patients in a prospective randomized clinical trial. Sixty PHN patients were divided into four groups (n = 15 each): the conventional puncture group (group CP), the nerve block therapy group (group NB), the PRF group (group PRF), and the combined treatment group (PRF combined with nerve block therapy (group CT). To evaluate the extent of remission of hyperalgesia, we recorded the visual analogue scale (VAS) scores during cotton swab reaction before and after treatment and in the resting and active pain states. In addition, blood samples were collected and plasma cytokine and neuropeptides such as interleukin-6 (IL-6), substance P (SP), and β-endorphin (β-EP) were measured by enzyme-linked immunosorbent assay (ELISA) at the admission (basic state), before the operation, and at 12 h postoperatively. The number of adverse events (nausea, vomiting, constipation, puncture point hemorrhage, swelling and redness) within 12 h of the treatment were also documented. Our results showed that VAS scores during cotton swab reaction decreased after treatment in all patients (p < 0.05). Compared to group CP, plasma IL-6 and SP levels decreased (p < 0.05) and β-EP levels increased (p < 0.05) in groups NB, PRF, and CT. There were no significant differences in adverse events among groups (p > 0.05). We found that PRF in combination with NBT increased β-EP levels and decreased plasma IL-6 and SP, thereby alleviating pain and hyperalgesia in PHN patients. Taken together, our data suggest combined therapy of PRF and NBT is effective and safe for PHN patients.

Vaccines for the elderly: current use and future challenges

Age-related changes of the immune system contribute to increased incidence and severity of infections in the elderly. Vaccination is the most effective measure to prevent infections and vaccination recommendations in most countries include specific guidelines for the elderly. Vaccination against influenza and Streptococcus pneumoniae is usually recommended for persons with underlying diseases and for the elderly with heterogeneous age limits between ≥ 50 years and ≥ 65 years. Some countries also recommend vaccination against herpes zoster. Several vaccines are recommended for all adults, such as regular booster shots against tetanus/diphtheria/pertussis/polio, or for specific groups, e.g. vaccination against tick-borne encephalitis in endemic areas or travel vaccines. These are also relevant for the elderly. Most currently used vaccines are less immunogenic and effective in the elderly compared to younger adults. Potential strategies to improve their immunogenicity include higher antigen dose, alternative routes of administration, and the use of adjuvants, which were all implemented for influenza vaccines, and induce moderately higher antibody concentrations. Research on universal vaccines against influenza and S. pneumoniae is ongoing in order to overcome the limitations of the current strain-specific vaccines. Respiratory syncytial virus causes significant morbidity in the elderly. Novel vaccines against this and other pathogens, for instance bacterial nosocomial infections, have tremendous potential impact on health in old age and are intensively studied by many academic and commercial organizations. In addition to novel vaccine developments, it is crucial to increase awareness for the importance of vaccination beyond the pediatric setting, as vaccination coverage is still far from optimal for the older population.

Postherpetic Neuralgia and Trigeminal Neuralgia

Postherpetic neuralgia (PHN) is an unpredictable complication of varicella zoster virus- (VZV-) induced herpes zoster (HZ) which often occurs in elderly and immunocompromised persons and which can induce psychosocial dysfunction and can negatively impact on quality of life. Preventive options for PHN include vaccination of high-risk persons against HZ, early use of antiviral agents, and robust management of pain during the early stage of acute herpes zoster. If it does occur, PHN may persist for months or even years after resolution of the HZ mucocutaneous eruptions, and treatment is often only partially effective. Classical trigeminal neuralgia is a severe orofacial neuropathic pain condition characterized by unilateral, brief but recurrent, lancinating paroxysmal pain confined to the distribution of one or more of the branches of the trigeminal nerve. It may be idiopathic or causally associated with vascular compression of the trigeminal nerve root. The anticonvulsive agents, carbamazepine or oxcarbazepine, constitute the first-line treatment. Microvascular decompression or ablative procedures should be considered when pharmacotherapy is ineffective or intolerable. The aim of this short review is briefly to discuss the etiopathogenesis, clinical features, and treatment of PHN and classical trigeminal neuralgia.

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.

An overview of pathways encoding nociception

The nervous system detects and interprets a variety of chemical, mechanical, and thermal stimuli. In the face of tissue injury, local inflammatory products perpetuate ongoing activity and sensitisation of the peripheral nerve termini. This ongoing activity evokes a state of robust spinal facilitation mediated by a number of local circuits, the net effect yielding an enhanced message of nociception to higher centres. This messaging typically wanes with the resolution of inflammation or wound healing. However, there are situations in which peripheral and central components of the pain transmission pathway extend and enhance the pain state, leading to a persistent hypersensitivity, e.g., an acute to chronic pain transition. Current work points to the contribution of innate and adaptive immunity in creating these enduring conditions. We briefly describe the underlying biological components of both physiological pain processing and pathological pain processing, as well as the acute to chronic pain transition and the role of innate and adaptive immunity in this transition.

Managing herpes zoster in older adults: Prescribing considerations

NPs must be aware of special prescribing considerations for medication safety when managing the care of older adults with herpes zoster. Age-related physiologic changes of the body impact the pharmacokinetics and pharmacodynamics of antiviral and pain medications and can lead to potential adverse events.

[The alpha-herpesviridae in dermatology : Varicella zoster virus. German version]

The second part of this publication deals with varicella zoster virus (VZV) and presents an overview of new, rare, and atypical clinical manifestations, including photolocalized varicella, hemorrhagic bullae during varicella, the implication of VZV in immunoglobulin A vasculitis, VZV-related alopecia, ulcerative varicella skin lesions, childhood herpes zoster (HZ), prolonged prodromal pains, recurrent HZ, VZV implication in burning mouth syndrome, verruciform VZV lesions, the significance of satellite lesions during HZ, and late HZ complications, either neurological or internal. Furthermore, certain associations between the occurrence of HZ and subsequent internal pathologies, as well as risk factors for HZ and new developments in vaccination against HZ will be addressed.

Infection, Pain, and Itch

Pain and itch are unpleasant sensations that often accompany infections caused by viral, bacterial, parasitic, and fungal pathogens. Recent studies show that sensory neurons are able to directly detect pathogens to mediate pain and itch. Nociceptor and pruriceptor neurons respond to pathogen-associated molecular patterns, including Toll-like receptor ligands, N-formyl peptides, and bacterial toxins. Other pathogens are able to silence neuronal activity to produce analgesia during infection. Pain and itch could lead to neuronal modulation of the immune system or behavioral avoidance of future pathogen exposure. Conversely, pathogens could modulate neuronal signaling to potentiate their pathogenesis and facilitate their spread to other hosts. Defining how pathogens modulate pain and itch has critical implications for sensory neurobiology and our understanding of host-microbe interactions.