Treatment of the Localized Pain of Postherpetic Neuralgia

Post herpetic neuralgia: A retrospective study to evaluate response to modified Jaipur block with increased concentration of dexamethasone

Background:

Postherpetic neuralgia (PHN) is a complication of herpes zoster characterized by persistent dermatomal pain. It has a negative impact on the quality of life. There is no gold standard therapy for PHN, and various local and systemic treatments have been tried. There are studies reporting the use of combination of steroids and local anesthetics but there is no standardized method.

Aim:

To evaluate the response of modified Jaipur block with increased concentration of dexamethasone.

Methods:

We conducted a retrospective study in patients who were given Jaipur block. The patients age, sex, duration of PHN, type and severity of pain were observed. A combination of 2% lignocaine and 0.5% bupivacaine and dexamethasone was injected subcutaneously. The pain was scored using visual analogue scale at the baseline, and 1 month after 1^st, 2^nd, and 3^rd session of block and follow up after 6 months and 1 year.

Results:

The mean age of our patient was 63.33 ± 9.5 years. The males outnumbered females. Thoracic dermatomes were more commonly involved. The mean duration of PHN was 11.58 ± 12.76 months; stimulus evoked PHN was the commonest type of pain seen. The mean visual analogue score (VAS) decreased progressively after each session of the block. Maximum patients (50%) had excellent response, whereas 1.9% did not respond to the block. Relapse of pain was seen in 5.6% of the patients. There was no significant side effect noted.

Limitations:

There was no objective method used to assess pain.

Conclusion:

PHN is chronic neuropathic pain. Response to modified Jaipur block is good, but if the duration of PHN is more, the recurrence rate is higher. Modified Jaipur block is an effective and safe treatment for PHN

Topical drug therapeutics for neuropathic pain

INTRODUCTION

Neuropathic pain (NP) is a particularly severe and intractable chronic condition that is not well treated by commonly recommended systemic pharmacological therapies, partly due to dose-limiting side effects or adverse events. The use of topical therapeutics for NP is growing and benefits from the reduced potential for adverse effects, as well as the ability to directly target peripheral pathological processes.

AREAS COVERED

The current review defines and describes the limitations of various commonly prescribed systemic pharmacological therapies for NP. It also provides a justification for increased research aimed at developing topical therapeutics for NP, particularly localized and peripheral NP. The review discusses the various classes of topical treatments used for NP, including agents that: block sensory inputs; activate inhibitory systems; provide mechanism-based therapeutics; are used in mucosal tissues; and include combinations that produce multimodal therapeutic effects.

EXPERT OPINION

There are arguments that the current topical therapeutics for NP rely too heavily on the use of local anesthetics and capsaicinoids, and more research is certainly needed on topical therapies that are multimodal and/or are targeted at the peripheral sources of pathology. The potential for novel topical therapeutics may be enhanced by further research on topical co-drugs, drug-drug salts, co-crystals and hydrates, and ionic liquids.

[Recommendations for treatment and prevention of herpes zoster and associated pain in aged adults]

Initiated within the first 72 hours of the rash, prescribing antiviral drugs reduces both acute neuralgia (AN) and later complications and especially postherpetic neuralgia (PHN). But their analgesic as well as preventative effect on AN and PHN is modest. Combination with analgesic drugs is more often needed for pain management. However, the pharmacological management of pain, in the context of old patients' frailty, co-morbidities and often polypharmacy, must be carefully considered. Based on analyses of the evidences from the literature, this review presents the therapeutic options we have at one's disposal and proposes a stepwise management for both AN and PHN specifically designed for aged population.

Morphine sensitivity of spinal neurons in the chronic constriction injury neuropathic rat pain model

Opioid analgesia involves suppression of neuronal activity in central sensory pathways. We show that the classic opioid morphine reduces spinal neuronal spontaneous and evoked activity after induction of neuropathy by chronic constriction injury of the sciatic nerve in rats. The minimal effective dose of morphine was 0.3 mg/kg for most response parameters tested. Morphine sensitivity of spinal cord neurons is similar across neuropathic pain models. We therefore conclude that nerve damage per se rather than the experimental model determines the effectiveness of opioids in general and investigate several pain measurement endpoints which might be important to clinically determine morphine's efficacy in neuropathic pain.

What is localized neuropathic pain? A first proposal to characterize and define a widely used term

SUMMARY According to several guidelines, topical agents should be considered for the pharmacological management of localized neuropathic pain. As a definition for the term ‘localized neuropathic pain’ that might facilitate easier identification of patients who are putatively responsive to topical treatments could not be found in the literature, six pain specialists met in 2010 to address this challenging issue. The following nucleus of a definition that is based on the International Association for the Study of Pain (IASP) definition of neuropathic pain, is the most detailed that can currently be proposed: ‘Localized neuropathic pain is a type of neuropathic pain that is characterized by consistent and circumscribed area(s) of maximum pain’. An extended version of this core definition and the difficulties in covering all aspects of localized neuropathic pain are presented, and discussions within the scientific community are encouraged to develop a definition that might help to identify patients who could benefit most from topical treatment.