Postherpetic trigeminal neuralgia

The Distributed Nociceptive System: A Framework for Understanding Pain

Chronic pain remains challenging to both diagnose and treat. These challenges, in part, arise from limited systems-level understanding of the basic mechanisms that process nociceptive information and ultimately instantiate a subjectively available experience of pain. Here, I provide a framework, the distributed nociceptive system, for understanding nociceptive mechanisms at a systems level by integrating the concepts of neural population coding with distributed processing. Within this framework, wide-spread engagement of populations of neurons produces representations of nociceptive information that are highly resilient to disruption. The distributed nociceptive system provides a foundation for understanding complex spatial aspects of chronic pain and provides an impetus for nonpharmacological cognitive and physical therapies that can effectively target the highly distributed system that gives rise to an experience of pain.

Contributions of Nociresponsive Area 3a to Normal and Abnormal Somatosensory Perception

Traditionally, cytoarchitectonic area 3a of primary somatosensory cortex (SI) has been regarded as a proprioceptive relay to motor cortex. However, neuronal spike-train recordings and optical intrinsic signal imaging, obtained from nonhuman sensorimotor cortex, show that neuronal activity in some of the cortical columns in area 3a can be readily triggered by a C-nociceptor afferent drive. These findings indicate that area 3a is a critical link in cerebral cortical encoding of secondary/slow pain. Also, area 3a contributes to abnormal pain processing in the presence of activity-dependent reversal of gamma-aminobutyric acid A receptor-mediated inhibition. Accordingly, abnormal processing within area 3a may contribute mechanistically to generation of clinical pain conditions. PERSPECTIVE: Optical imaging and neurophysiological mapping of area 3a of SI has revealed substantial driving from unmyelinated cutaneous nociceptors, complementing input to areas 3b and 1 of SI from myelinated nociceptors and non-nociceptors. These and related findings force a reconsideration of mechanisms for SI processing of pain.

Postherpetic Neuralgia

This article reviews the definition, epidemiology, pathology, clinical features, and treatment of postherpetic neuralgia (PHN). Much of this information is well established. However, there is some important new information about the pathology that may shed light on the pathogenesis of this disorder. The exciting prospect exists of the prevention of PHN by vaccination and by early, aggressive treatment of herpes zoster. This is important because current treatment approaches have significant limitations. We now have certain antidepressants, anticonvulsants, opioids, and the topical agent lidocaine that have been scientifically shown by randomized controlled trials to be effective in this disorder. However, all of these have a modest effect at best and newer treatments are necessary. Prevention may be very important for the 30% to 50% of the patients who either do not respond at all or do not respond well. Regional anesthetic procedures do not have a good scientific basis for either acute zoster or established PHN, but remain a reasonable alternative for some patients. This article addresses the issue of how effective the current treatments really are and gives practical guidelines for management.

Pain caused by herpes zoster infection

Postherpetic neuralgia (PHN) is a neuropathic pain disorder that occurs most often in the elderly. This painful condition is uniquely suited for clinical research, resulting in an emerging understanding of the pathophysiology of the persistent pain. Until recently, only the tricyclic antidepressants proved effective for PHN. Controlled trials of a wide variety of therapeutic strategies are in progress or have been recently completed.

Current and Future Management of Herpes Zoster

Herpes zoster (shingles) is a common disease affecting approximately three in 1000 of the population per year and up to 10 in 1000 per year in the elderly population. This incidence is likely to increase as the proportion of elderly people in the general population increases and various forms of immunosuppression become more common, e.g. following organ transplantation. Management of both the acute and chronic pain is probably the most important part of caring for shingles patients. Antiviral therapy, anti-inflammatory steroids and sympathetic nerve blocks are the main measures used during the acute phase to prevent the development of postherpetic neuralgia (PHN). Antiviral agents given early in the acute phase of herpes zoster are generally the therapy of choice and there is also growing evidence for benefit with tricyclic antidepressants. Pain relief once PHN has developed is generally much less effective. Many classes of drug have been investigated for the management of PHN and some have been found to be helpful in some patients. There is as yet no generally effective agent, however preventive antiviral therapy early in the course of herpes zoster is recommended for all elderly patients since they have a high risk of developing severe PHN.

The Duke experience with the nucleus caudalis DREZ operation

The nucleus caudalis DREZ operation has been performed in three phases at Duke. Between 1982 and 1988 radiofrequency (RF) lesions were made in the trigeminal nucleus extending from the C2 root to the obex using a straight electrode. Complications include ipsilateral arm ataxia due to spinocerebellar tract injury and ipsilateral lower limb weakness from the pyramidal tract. The former occurred at least transiently in 90% of cases. The electrode employed from 1988 to 1989 had proximal insulation protecting the spinocerebellar tract. Since 1989 a ninety degree bend has been added to the electrode to allow better placement. Two electrodes are used to accommodate the shape of the caudalis nucleus. A total of 101 procedures have been performed. The newest electrodes were used in 46 procedures. Ataxia is recognized in 39%. Overall pain relief was excellent in 34% and good in 40%. In post herpetic neuralgia 71% enjoyed excellent or good relief. Indications include post herpetic neuralgia, deafferentation pain (anaesthesia dolorosa, post-tic dysesthesia, stroke, MS, gasserian tumour, Gamma Knife radiation injury), facial trauma/surgery, atypical facial pain, and migraine/cluster headache. A study to compare this operation to deep brain stimulation prospectively for the above indications has been initiated.

Human infection with herpes zoster: etiology, pathophysiology, diagnosis, clinical course, and treatment

Herpes zoster is a cutaneous vesicular eruption resulting from recrudescence of the chickenpox virus. It is mainly a disease of adults, with a predisposition for the elderly or immunocompromised. Although usually localized, the disease can disseminate to visceral organs. Diagnosis is often made based on the characteristic pattern of the lesion and clinical features. Tzanck smear, viral isolation, seroconversion, antibody titers, and monoclonal antibodies may further aid or confirm the diagnosis. Clinical features of herpes zoster may follow a progression through 3 stages, prodromal, acute, and chronic. The prodromal and acute phases seldom require more than symptomatic management. The chronic pain syndrome, postherpetic neuralgia (PHN), demands a more aggressive approach. Pharmacologic intervention, neuroaugmentation, and/or surgery may prevent or alleviate PHN, but universal response to any of these therapeutic approaches is unlikely. Tricyclic antidepressants remain the first choice in treating this pain syndrome. A trial of antiviral therapy may be warranted in patients with disseminated disease or in immunocompromised patients with localized disease. Of the antiviral agents, acyclovir is considered the drug of choice by most clinicians.

Acute herpetic and postherpetic neuralgia: clinical review and current management

The pain of acute herpes zoster (HZ) may be severe, but it is usually transitory. A minority of patients, with the elderly at particular risk, go on to develop persistent, severe, often disabling pain called postherpetic neuralgia. Though the clinical features of these conditions are well known, the pathology of PHN is poorly described and the pathogenesis of the pain in both remains conjectural. During the past 60 years, an extraordinary number of pharmacological, anesthetic, and surgical therapies have been applied in an attempt to ameliorate the symptoms of acute herpes zoster, enhance its healing, prevent its transition to postherpetic neuralgia, and treat the pain of those with this complication. Relatively few treatments have been studied in a controlled manner, and fully reliable, safe, and effective therapeutic approaches for preventing and treating postherpetic neuralgia have not yet been found. This review summarizes current information on the epidemiology, clinical features, and pathology of herpes zoster and postherpetic neuralgia, and critically examines the accumulated experience with the various treatments. Guidelines for management are suggested.

The management of postherpetic neuralgia with chlorprothixene

Sixteen patients with established postherpetic pain were treated with chlorprothixene. Several other pain problems were simultaneously treated. Chlorprothixene was found to produce a favorable pain response in most patients with postherpetic pain while failing to be of value in other clinical pain problems. Chlorprothixene may be a satisfactory drug for the control of spinal or ophthalmic postherpetic pain.

Stereotaxic trigeminal tractotomy for post-herpetic facial pain

✓ The development of accurate techniques for spinal stereotaxic surgery facilitates the difficult management of post-herpetic facial pain by making possible destruction of both the spinal trigeminal nucleus and descending tract; it also elminates excitation from the nuclear overlap between cervical and facial segments and intranuclear pathways. The technique is described and three cases reported. Stereotaxic trigeminal tractotomy relieves both the hyperpathia and deep background pain of herpes.