Treatment options in postherpetic neuralgia

Knockdown siRNA Targeting GPR55 Reveals Significant Differences Between the Anti-inflammatory Actions of KLS-13019 and Cannabidiol

KLS-13019 was reported previously to reverse paclitaxel-induced mechanical allodynia in a mouse model of chemotherapy-induced peripheral neuropathy (CIPN). Recent studies demonstrated that paclitaxel-induced increases in inflammatory markers (GPR55, NLRP3, and IL-1β) of dorsal root ganglion (DRG) cultures were shown to be reversed by KLS-13019 treatment. The mechanism of action for KLS-13019-mediated reversal of paclitaxel-induced neuroinflammation now has been explored using GPR55 siRNA. Pre-treatment of DRG cultures with GPR55 siRNA produced a 21% decrease of immunoreactive (IR) area for GPR55 in cell bodies and a 59% decrease in neuritic IR area, as determined by high-content imaging. Using a 24-h reversal treatment paradigm, paclitaxel-induced increases in the inflammatory markers were reversed back to control levels after KLS-3019 treatment. Decreases in these inflammatory markers produced by KLS-13019 were significantly attenuated by GPR55 siRNA co-treatment, with mean IR area responses being attenuated by 56% in neurites and 53% in cell bodies. These data indicate that the percentage decreases in siRNA-mediated attenuation of KLS-13019-related efficacy on the inflammatory markers were similar to the percentage knockdown observed for neuritic GPR55 IR area. Similar studies conducted with cannabidiol (CBD), the parent compound of KLS-13019, produced low efficacy (25%) reversal of all inflammatory markers that were poorly attenuated (29%) by GPR55 siRNA. CBD was shown previously to be ineffective in reversing paclitaxel-induced mechanical allodynia. The present studies indicated significant differences between the anti-inflammatory properties of KLS-13019 and CBD which may play a role in their observed differences in the reversibility of mechanical allodynia in a mouse model of CIPN.

Knockdown siRNA targeting GPR55 reveals significant differences between the anti-inflammatory actions of KLS-13019 and cannabidiol

KLS-13019 was reported previously to reverse paclitaxel-induced mechanical allodynia in a mouse model of chemotherapy-induced peripheral neuropathy (CIPN). Recent studies demonstrated that paclitaxel-induced increases in inflammatory markers (GPR55, NLRP3 and IL-1b) of dorsal root ganglion (DRG) cultures were shown to be reversed by KLS-13019 treatment. The mechanism of action for KLS-13019-mediated reversal of paclitaxel-induced neuroinflammation now has been explored using GPR55 siRNA. Pretreatment of DRG cultures with GPR55 siRNA produced a 21% decrease of immunoreactive (IR) area for GPR55 in cell bodies and a 59% decrease in neuritic IR area, as determined by high content imaging. Using a 24-hour reversal treatment paradigm, paclitaxel-induced increases in the inflammatory markers were reversed back to control levels after KLS-3019 treatment. Decreases in these inflammatory markers produced by KLS-13019 were significantly attenuated by GPR55 siRNA co-treatment, with mean IR area responses being attenuated by 56% in neurites and 53% in cell bodies. These data indicate that the percentage decreases in siRNA-mediated attenuation of KLS-13019-related efficacy on the inflammatory markers were similar to the percentage knockdown observed for neuritic GPR55 IR area. Similar studies conducted with cannabidiol (CBD), the parent compound of KLS-13019, produced low efficacy (25%) reversal of all inflammatory markers that were poorly attenuated (29%) by GPR55 siRNA. CBD was shown previously to be ineffective in reversing paclitaxel-induced mechanical allodynia. The present studies indicated significant differences between the anti-inflammatory properties of KLS-13019 and CBD which may play a role in their observed differences in the reversibility of mechanical allodynia in a mouse model of CIPN.

A randomised sham-controlled study evaluating rTMS analgesic efficacy for postherpetic neuralgia

Context

Postherpetic neuralgia (PHN) is a refractory neuropathic pain condition in which new treatment options are being developed. Repetitive transcranial magnetic stimulation (rTMS) may have the potential to reduce pain sensations in patients with postherpetic neuralgia.

Objectives

This study investigated the efficacy on postherpetic neuralgia by stimulating two potential targets, the motor cortex (M1) and the dorsolateral prefrontal cortex (DLPFC).

Methods

This is a double-blind, randomised, sham-controlled study. Potential participants were recruited from Hangzhou First People's Hospital. Patients were randomly assigned to either the M1, DLPFC or Sham group. Patients received ten daily sessions of 10-Hz rTMS in 2 consecutive weeks. The primary outcome measure was visual analogue scale (VAS) assessed at baseline, first week of treatment (week 1), post-treatment (week 2), 1-week (week 4), 1-month (week 6) and 3-month (week 14) follow-up.

Results

Of sixty patients enrolled, 51 received treatment and completed all outcome assessments. M1 stimulation resulted in a larger analgesia during and after treatment compared to the Sham (week 2 - week 14, p < 0.005), as well as to the DLPFC stimulation (week 1 - week 14, p < 0.05). In addition to pain, sleep disturbance was significantly improved and relieved by targeting either the M1 or the DLPFC (M1: week 4 - week 14, p < 0.01; DLPFC: week 4 - week 14, p < 0.01). Moreover, pain sensations following M1 stimulation uniquely predicted improvement in sleep quality.

Conclusion

M1 rTMS is superior to DLPFC stimulation in treating PHN with excellent pain response and long-term analgesia. Meanwhile, M1 and DLPFC stimulation were equally effective in improving sleep quality in PHN.

Clinical trial registration

https://www.chictr.org.cn/, identifier ChiCTR2100051963.

Anti-Inflammatory Properties of KLS-13019: a Novel GPR55 Antagonist for Dorsal Root Ganglion and Hippocampal Cultures

KLS-13019, a novel devised cannabinoid-like compound, was explored for anti-inflammatory actions in dorsal root ganglion cultures relevant to chemotherapy-induced peripheral neuropathy (CIPN). Time course studies with 3 µM paclitaxel indicated > 1.9-fold increases in immunoreactive (IR) area for cell body GPR55 after 30 min as determined by high content imaging. To test for reversibility of paclitaxel-induced increases in GPR55, cultures were treated for 8 h with paclitaxel alone and then a dose response to KLS-13019 added for another 16 h. This "reversal" paradigm indicated established increases in cell body GPR55 IR areas were decreased back to control levels. Because GPR55 had previously reported inflammatory actions, IL-1β and NLRP3 (inflammasome-3 marker) were also measured in the "reversal" paradigm. Significant increases in all inflammatory markers were produced after 8 h of paclitaxel treatment alone that were reversed to control levels with KLS-13019 treatment. Accompanying studies using alamar blue indicated that decreased cellular viability produced by paclitaxel treatment was reverted back to control levels by KLS-13019. Similar studies conducted with lysophosphatidylinositol (GPR55 agonist) in DRG or hippocampal cultures demonstrated significant increases in neuritic GPR55, NLRP3 and IL-1β areas that were reversed to control levels with KLS-13019 treatment. Studies with a human GPR55-β-arrestin assay in Discover X cells indicated that KLS-13019 was an antagonist without agonist activity. These studies indicated that KLS-13019 has anti-inflammatory properties mediated through GPR55 antagonist actions. Together with previous studies, KLS-13019 is a potent neuroprotective, anti-inflammatory cannabinoid with therapeutic potential for high efficacy treatment of neuropathic pain.

Modulation of serum BDNF levels in postherpetic neuralgia following pulsed radiofrequency of intercostal nerve and pregabalin

Aim: To study the modulation of serum BDNF levels following integrated multimodal intervention in postherpetic neuralgia (PHN). Materials & methods: A randomized, double-blind controlled study was undertaken among patients of thoracic PHN where 30 patients received pregabalin with pulsed radiofrequency and 30 controls received pregabalin with sham treatment. Results: Pain intensity (visual analog scale) was reduced earlier in intervention group (15.3 ± 5.7 at the fourth week) compared with control group (16.3 ± 6.6 at the eighth week). Serum BDNF level increased with time in both the groups with overall increase more pronounced in intervention group. Conclusion: Integrated multimodal therapy using minimally invasive pulsed radiofrequency and pregabalin in PHN was effective in early pain reduction with elevated serum BDNF levels.

The journey to chronic pain: a grounded theory of older adults' experiences of pain associated with leg ulceration

This study aimed to develop a grounded theory to describe and explain the experience of pain and its impact, as reported by the individuals who had pain associated with chronic leg ulceration. The Strauss and Corbin grounded theory approach was used. In-depth interviews were undertaken with 11 people aged ≥ 65 years from Leeds in the north of England. All participants were cared for by home care nurses and had painful leg ulceration. The emergent grounded theory centered on a core category of "The journey to chronic pain." The theory suggested a trajectory consisting of three phases that the patient experiences, where the end result is a chronic pain syndrome. In phase 1, leg ulcer pain has predominantly acute nociceptive properties, and if this is not managed effectively, or ulcers do not heal, persistent pain may develop with both nociceptive and neuropathic properties (i.e., phase 2). If phase 2 pain is not managed effectively, patients may then develop refractory long-term pain (phase 3). Those who progress to phase 3 tend to experience negative consequences such as insomnia, depression, and suicidal ideation. Only when health care professionals understand and acknowledge the persistent and long-term nature of the pain in this patient group can the pain be managed effectively.

Clinical characteristics and patterns of healthcare utilization in patients with painful neuropathic disorders in UK general practice: a retrospective cohort study

BACKGROUND

Clinical characteristics and patterns of healthcare utilization in patients with painful neuropathic disorders (PNDs) who are under the care of general practitioners (GPs) in the UK are not well understood.

METHODS

Using a large electronic UK database, we identified all adults (age ≥ 18 years) with any GP encounters between 1 January 2006-31 December 2006 at which a diagnosis of PND was noted ("PND patients"). An age-and gender-matched comparison group also was constituted consisting of randomly selected patients with one or more GP encounters-but no mention of PNDs-during this period. Characteristics and patterns of healthcare utilization of patients in the two groups were then examined over the one-year study period.

RESULTS

The study sample consisted of 31,688 patients with mention of PNDs and an equal number of matched comparators; mean age was 56 years, and 62% were women. The prevalence of various comorbidities was higher among patients in the PND group, including digestive disorders (31% vs. 17% for comparison group), circulatory disorders (29% vs. 22%), and depression (4% vs. 3%) (all p < 0.01). Receipt of prescriptions for pain-related pharmacotherapy also was higher among PND patients, including nonsteroidal anti-inflammatory drugs (56% of PND patients had one or more such prescriptions vs. only 22% in the comparison group), opioids (49% vs. 12%), tricyclic antidepressants (20% vs. 1%), and antiepileptics (12% vs. 1%) (all p < 0.01). PND patients also averaged significantly more GP visits (22.8 vs. 14.2) and referrals to specialists (2.8 vs. 1.4) over one year (both comparisons p < 0.01).

CONCLUSIONS

Patients with PNDs under the care of GPs in the UK have relatively high levels of use of healthcare services and pain-related pharmacotherapy.

The use of narrow band ultraviolet light B in the prevention and treatment of postherpetic neuralgia (a pilot study)

Background:

Postherpetic neuralgia (PHN) is a common complication of herpes zoster that is frequently unresponsive to most of the available treatment modalities. Broad band ultraviolet B radiation (UVB) has a well-known anti-inflammatory effect. Moreover, it decreases neural damage and cutaneous nerve density. It was found that broad band UVB might have a role in the prevention and treatment of PHN.

Aim:

This study was carried out to evaluate the effect ofnarrow band UVB (nbUVB) in the treatment PHN.

Patients and Methods:

The study included 17 patients with distressing post herpetic neuralgia. Patients were evaluated using the Verbal Rating Scale (VRS). The patients received nbUVB sessions, three times a week, for a total of 15 sessions or until the pain disappeared. Patients were followed up for a period of 3 months after the end of therapy.

Results:

Using intention to treat analysis, more than 50% improvement was achieved in 6 (35.29%) and 8 (47.06%) patients, at the end of therapy and after 3 months follow up, respectively. An improvement less that 50% was achieved in 11 (64.71%) and 9 (52.94%) patients, at the end of therapy and after 3 months follow up, respectively. The pain severity assessed by the VRS significantly improved both at the end of sessions (P = 0.005) and after 3 months follow up (P = 0.005).

Conclusion:

nbUVB may be of beneficial use in the treatment of PHN.

Limitation:

Small number of patients and limited follow-up period.

The effect of Gunn's intramuscular stimulation for postherpetic neuralgia -A report of 4 cases-

Herpes zoster is the consequence of reactivation of latent varicella zoster virus from dorsal root ganglia. Postherpetic neuralgia (PHN) may be diagnosed when pain persists in a dermatomal pattern long after the vesicular erruption has healed. PHN is a kind of neuropathic pain. The pathophysiology of PHN is uncertain, but neuropathic pain due to denervation supersensitivity may be important to understand the pathophysiology of PHN. Numerous treatment have been introduced for the management of PHN, but no methods that results in complete remission. Gunn's intramuscular stimulation (IMS) is one of the best treatment of chronic pain, especially neuropathic pain. We tried Gunn's IMS for treatment of PHN patients affecting thoracic dermatomes. As a result, the visual analogue scale (VAS) was decreased from 7-8 to 2-3 and the result were satisfactory. The purpose of this case report is to introduce the Gunn's IMS and review our experience for the treatment of PHN.

Efficacy of pregabalin in neuropathic pain in paediatric oncological patients

OBJECTIVE

To evaluate the safety and efficacy of pregabalin in the management of chemotherapy-induced neuropathic pain in patients with childhood solid tumors and leukaemia.

MATERIALS AND METHODS

In an open-label study, 30 children (11 boys and 19 girls; mean age 13.5 years) who were treated for solid tumors and leukaemia, and developed a painful peripheral neuropathy, were medicated with pregabalin in the daily dose of 150-300 mg for 8 weeks.

RESULTS

Twenty-eight patients completed the 8-week follow-up. A significant and long-lasting pain relief was noted in 86% of these patients. Median VAS score decreased by 59% at the 8th week from baseline. Adverse effects were infrequent and transient.

CONCLUSION

The treatment with pregabalin resulted in a significant improvement in pain symptoms. The use of pregabalin in children is off-label so far. However, this drug seems to be a safe and effective remedy, which could significantly broaden the therapeutic spectrum in paediatric oncological patients suffering from neuropathic pain.

Clinical and economic characteristics of patients with painful neuropathic disorders in Germany

Using a large database with information from general practitioners (GP) throughout Germany, we identified all adults (age > or = 18 years) with encounters for painful neuropathic disorders (PNDs) between August 1, 2005 and July 31, 2006 (PND patients). We also constituted an age- and sex-matched comparison group, consisting of randomly selected patients without any GP encounters for PNDs during the same period. Selected characteristics were then compared between PND patients and those in the comparison group over the 1-year study period. The study sample consisted of 275,685 PND patients and a similar number in the matched comparison group; mean age was 53.7 years, and 57% were women. PND patients were more likely than matched comparators to have encounters for various comorbidities, including circulatory system disorders (47% vs. 20%, respectively), depression (9% vs. 2%), and anxiety (4% vs. 1%) (all P < 0.01). They also were more likely to have received pain-related medications (57% vs. 13% for comparison group; P < 0.01)--most commonly, nonsteroidal anti-inflammatory drugs, benzodiazepines, and opioids, and less often, tricyclic antidepressants and anti-epileptics. PND patients averaged 7.3 more GP visits during the year (mean [95% CI] = 9.9 [9.9, 9.9] vs. 2.6 [2.6, 2.7] for comparison group); they also had significantly more specialist referrals and physician-excused absences from work (all P < 0.01). Patients with PNDs under the care of GPs in Germany have comparatively more comorbidities and higher levels of use of healthcare services. The pain-related medications that these patients receive raise concerns that PNDs may not be optimally treated in these settings.

Pregabalin for relief of neuropathic pain associated with diabetic neuropathy: a randomized, double-blind study

Seven published, randomized, placebo-controlled clinical trials with pregabalin have shown robust efficacy for relief of neuropathic pain from DPN and PHN. An investigation of the efficacy and safety of twice daily pregabalin enrolled 395 adults with painful DPN for > or = 1 year in a 12-week, double-blind, placebo-controlled trial. Patients were randomized to placebo, 150, 300, or 600 mg/day pregabalin (n = 96, 99, 99, and 101). Primary efficacy measure was change from baseline in endpoint mean pain score from patients' daily pain diaries. Secondary efficacy measures included pain-related sleep-interference scores, Patient and Clinical Global Impressions of Change (PGIC, CGIC), and the EuroQOL Health Utilities Index (EQ-5D). Statistically significant reduction in pain was observed in patients receiving pregabalin 600 mg/day, and 46% of patients treated with 600 mg/day pregabalin reported > or = 50% improvement in mean pain scores from baseline (vs 30% of placebo patients, p = 0.036). Number needed to treat to achieve such response was 6.3. Pregabalin 600 mg/day was significantly superior to placebo in improving pain-related sleep-interference scores (p = 0.003), PGIC (p = 0.021), and CGIC (p = 0.009). (Neither pregabalin 150 nor 300 mg/day separated from placebo on these measures, largely because of an atypically large placebo response in one country representing 42% of patients.) All pregabalin dosages were superior to placebo in improving EQ-5D utility scores (all p > or = 0.0263 vs placebo). Pregabalin was well tolerated at all dosages; adverse events were generally mild to moderate. Number needed to harm (discontinuation because of adverse events) was 10.3 for pregabalin 600 mg/day.

Management of painful neuropathies

Inadequately assessed and poorly managed pain contributes both to high general medical cost and to increasing numbers of societal problems. A large determining factor of inadequate pain care is the lack of understanding about the complex nature of pain and of a rational approach to its assessment and treatment. The less than adequate assessment of neuropathic pain and its relatively poor response to typical analgesic medications are major determinants to the undertreatment of pain. Other than the important management concept of treating the underlying cause, current approaches to the treatment of pain in general, and neuropathic pain in particular, have shifted away from treatment of individual syndromes toward the identification and management of common symptoms and the mechanisms upon which such symptoms are presumed to be based. This article summarizes the features of neuropathic pain that commonly appear in most peripheral neuropathies, regardless of the mechanism of injury, and provides an approach for the selection of treatment.

Managing pain after shingles: a nursing perspective

Post-herpetic neuralgia (PHN) is the neuropathic pain syndrome that may develop following an attack of shingles. While for many the symptoms subside, there can be long-term pain problems for up to 40% of those affected with PHN, and for 3% of these, symptoms can be severe (Dworkin and Portenoy, 1996). Knowledge and understanding of the symptoms and various treatments and approaches available is important to enable nurses and patients to work together in partnership to achieve the best outcomes. Realizing that more than one approach may be needed can allow for treatments which are complementary and for optimization of both biomedical and self-care approaches.

Use of tricyclic antidepressants in older patients with painful neuropathies

OBJECTIVE

To describe patterns of use of tricyclic antidepressants (TCAs) (e.g., amitriptyline, nortriptyline) in older patients with painful neuropathies.

RESEARCH DESIGN AND METHODS

Using a large US health insurance claims database, we identified all persons who: (1) received a TCA between 1 January 1999 and 30 June 2001, (2) were aged > or =65 years as of the date of their first prescription for a TCA during this period, and (3) had one or more health care encounters for the treatment of a painful neuropathy in the 30-day period immediately preceding their initial receipt of a TCA. We then examined the prevalence of selected comorbidities and/or concurrent use of medications that might render the prescribing of a TCA inappropriate, based on a listing of contraindications, warnings, and precautions found in the package inserts for these agents. Patterns of TCA use also were examined, based on information on paid claims.

RESULTS

A total of 1,732 patients met all inclusion and exclusion criteria for the study. Their mean age was 74.6 years; 60.3% were women. Amitriptyline was the most frequently prescribed TCA (79.4% of patients). Forty-one percent of study subjects receiving TCAs had conditions--primarily cardiovascular--that render the use of such agents potentially inappropriate. The mean daily dose of TCAs was universally low (about 23 mg).

CONCLUSIONS

The high prevalence of conditions rendering the use of TCAs potentially inappropriate, along with relatively low daily dosages, suggest that many older patients with painful neuropathies who are prescribed these agents may be suboptimally treated.

Gabapentin for the Symptomatic Treatment of Chronic Neuropathic Pain in Patients with Late-Stage Lyme Borreliosis: A Pilot Study

BACKGROUND

Chronic neuropathic pain occurs in 10-15% of patients with neuroborreliosis and is difficult to treat.

OBJECTIVE

We evaluated the effect of gabapentin monotherapy on residual pain in patients with neuroborreliosis after intravenous ceftriaxone treatment.

METHODS

Ten patients with neuroborreliosis and a long-lasting history of neurologic symptoms were treated with gabapentin, starting with 300 mg/day. Doses were raised over a period of 4-12 weeks to the individually effective and tolerated maximum dose (500-1,200 mg). Treatment was maintained until pain disappeared and then gradually reduced in dose over weeks. If symptoms recurred, the doses were raised again. Therapy was maintained over an average of 1-2 years.

RESULTS

Pain quality and pain quantity were evaluated using the McGill pain questionnaire and a visual analogue scale. There was an improvement of 'crawling' and 'burning' pain sensations, neck and radiating lumbar pain in 9/10 (90%) patients as well as a positive effect on mood, general feeling of health and quality of sleep in 5/10 (50%) patients. The average dose leading to a clear-cut pain reduction was 700 mg.

CONCLUSIONS

In an open pilot study (10 patients), gabapentin monotherapy which has to our knowledge not been published as treatment of chronic neuropathic pain in patients with late Lyme borreliosis is efficacious in treating pain associated with neuroborreliosis and can thus improve quality of life in these patients.

Chronic neuropathic pain. Mechanisms, diagnosis, and treatment

BACKGROUND

The management of chronic pain represents a significant public health issue in the United States. It is both costly to our health care system and devastating to the patient's quality of life. The need to improve pain outcomes is reflected by the congressional declaration of the present decade as the "Decade of Pain Control and Research," and the acknowledgment in January 2001 of pain as the "fifth vital sign" by the Joint Commission of Healthcare Organizations.

REVIEW SUMMARY

At present, therapeutic options are largely limited to drugs approved for other conditions, including anticonvulsants, antidepressants, antiarrhythmics, and opioids. However, treatment based on the underlying disease state (eg, postherpetic neuralgia, diabetic neuropathy) may be less than optimal, in that 2 patients with the same neuropathic pain syndrome may have different symptomatology and thus respond differently to the same treatment. Increases in our understanding of the function of the neurologic system over the last few years have led to new insights into the mechanisms underlying pain symptoms, especially chronic and neuropathic pain.

CONCLUSIONS

The rapidly evolving symptom- and mechanism-based approach to the treatment of neuropathic pain holds promise for improving the quality of life of our patients with neuropathic pain.

Critical review of oral drug treatments for diabetic neuropathic pain-clinical outcomes based on efficacy and safety data from placebo-controlled and direct comparative studies

The present review aims to evaluate the efficacy and safety of a selection of oral treatments for the management of painful diabetic neuropathy. A literature review was conducted retrieving placebo-controlled and direct comparative studies with a selection of oral treatments for painful diabetic neuropathy. All studies were analyzed with regard to efficacy and tolerability. Efficacy was evaluated as the percentage improvement in pain intensity between baseline and endpoint. Tolerability was evaluated by means of study discontinuations due to adverse events and by incidence of drug-related adverse events. The analyzed trials enrolled different patient populations with mostly small numbers of patients. The great variability in dosages and dose titration schemes, cross-over designs with variable wash-out periods, and other design schemes made comparison between the different studies difficult. Gabapentin, lamotrigine, tramadol, oxycodone, mexiletine, and acetyl-L-carnitine were the only treatments studied in large (at least 100 patients), placebo-controlled parallel group trials.It is concluded that standardization in design and reporting for comparison of treatments is needed. Validated questionnaires for evaluation of the efficacy and safety should be further developed. Based on the reviewed randomised controlled trials, gabapentin shows good efficacy, a favourable side-effect profile with lack of drug interactions and therefore it may be a first choice treatment in painful diabetic neuropathy, especially in the elderly. However, head to head trials of current treatments are lacking and therefore randomized controlled trials are required to address this issue.

Allodynia in rats infected with varicella zoster virus—a small animal model for post-herpetic neuralgia

The most common complication of herpes zoster is post-herpetic neuralgia (PHN), which has been defined as severe pain occurring 1 month after rash onset or persisting for greater than 3 months. PHN is classed as a neuropathic pain that is associated with mechanical allodynia where normally innocuous tactile stimuli are perceived as painful. The development of therapies to treat PHN has been hampered by the lack of animal models, which mimic the clinical situation. We have previously reported that varicella zoster virus (VZV) infection in the rat results in mechanical allodynia and thermal hyperalgesia. Here, we report that following VZV infection of the left footpad rats develop a chronic mechanical allodynia, which is present for longer than 60 days post-infection and which resolves by 100 days PI. The model is robust and reproducible with animals consistently developing allodynia by 3 days PI and continuing to present with symptoms for at least 30 days. The reproducible nature of the induction and course of the allodynia allows the use of this model to determine the effect of various compounds on, and to investigate the pathogenic mechanisms underlying the development of VZV-induced allodynia. Comparative studies using HSV-1 show that the induction of the chronic allodynia is VZV-specific and is not a result is of virus replication-induced tissue damage or accompanying inflammation. Therefore, we propose that the rat VZV infection model could prove useful in studying the mechanisms underlying post-herpetic neuralgia.

Peripheral Stimulation for Treatment of Trigeminal Postherpetic Neuralgia and Trigeminal Posttraumatic Neuropathic Pain: A Pilot Study

OBJECTIVE:

Trigeminal neuropathic pain (TNP) after facial trauma or herpes zoster infection is often refractory to treatment. Peripheral nerve stimulation has been used to treat occipital neuralgia; however, efficacy in controlling facial TNP or postherpetic neuralgia is unknown. A retrospective case series of patients who underwent subcutaneous placement of stimulating electrodes for treatment of V1 or V2 TNP secondary to herpetic infection or facial trauma is presented.

METHODS:

Ten patients received implanted subcutaneous pulse generators and quadripolar electrodes for peripheral stimulation of the trigeminal nerve supraorbital or infraorbital branches. Long-term treatment results were determined by retrospective review of medical records (1998–2003) and by independent observers interviewing patients using a standard questionnaire. Surgical complication rate, preoperative symptom duration, degree of pain relief, preoperative and postoperative work status, postoperative changes in medication usage, and overall degree of therapy satisfaction were assessed. Mean follow-up was 26.6 ± 4.7 months.

RESULTS:

Peripheral nerve stimulation provided at least 50% pain relief in 70% of patients with TNP or postherpetic neuralgia. Medication use declined in 70% of patients, and 80% indicated that they were mostly or completely satisfied with treatment overall. There were no treatment failures (&lt; 50% pain relief and a lack of decrease in medication use) in the posttraumatic group, and two failures (50%) occurred in the postherpetic group. The complication rate requiring reoperation was 30%.

CONCLUSION:

Peripheral nerve stimulation of the supraorbital or infraorbital branches of the trigeminal nerve is an effective method for relief of TNP after facial trauma or herpetic infection. A prospective trial using this novel approach to treat these disorders is thus warranted.

Myofascial pain disorders: theory to therapy

Voluntary muscle is the largest human organ system. The musculotendinous contractual unit sustains posture against gravity and actuates movement against inertia. Muscular injury can occur when soft tissues are exposed to single or recurrent episodes of biomechanical overloading. Muscular pain is often attributed to a myofascial pain disorder, a condition originally described by Drs Janet Travell and David Simons. Among patients seeking treatment from a variety of medical specialists, myofascial pain has been reported to vary from 30% to 93% depending on the subspecialty practice and setting. Forty-four million Americans are estimated to have myofascial pain; however, controversy exists between medical specialists regarding the diagnostic criteria for myofascial pain disorders and their existence as a pathological entity. Muscles with activity or injury-related pain are usually abnormally shortened with increased tone and tension. In addition, myofascial pain disorders are characterised by the presence of tender, firm nodules called trigger points. Within each trigger point is a hyperirritable spot, the 'taut-band', which is composed of hypercontracted extrafusal muscle fibres. Palpation of this spot within the trigger point provokes radiating, aching-type pain into localised reference zones. Research suggests that myofascial pain and dysfunction with characteristic trigger points and taut-bands are a spinal reflex disorder caused by a reverberating circuit of sustained neural activity in a specific spinal cord segment. The treatment of myofascial pain disorders requires that symptomatic trigger points and muscles are identified as primary or ancillary pain generators. Mechanical, thermal and chemical treatments, which neurophysiologically or physically denervate the neural loop of the trigger point, can result in reduced pain and temporary resolution of muscular overcontraction. Most experts believe that appropriate treatment should be directed at the trigger point to restore normal muscle length and proper biomechanical orientation of myofascial elements, followed by treatment that includes strengthening and stretching of the affected muscle. Chronic myofascial pain is usually a product of both physical and psychosocial influences that complicate convalescence.

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.

Change in opioid use after the initiation of gabapentin therapy in patients with postherpetic neuralgia

BACKGROUND

Postherpetic neuralgia (PHN) is a chronic painful disorder that sometimes develops after an acute episode of herpes zoster infection (shingles) and can be difficult to treat. Although opioids are sometimes effective for chronic neuropathic pain, adverse effects are common, particularly among the elderly, and may cause many patients to discontinue therapy.

OBJECTIVE

This study examined changes in opioid use after the initiation of gabapentin therapy in patients with PHN.

METHODS

A health insurance claims database was used to identify all persons aged >or= 18 years who began therapy with gabapentin in 2000 or 2001 and had either (1) >or=2 medical claims with a diagnosis of PHN during the 6-month period before the first receipt of gabapentin (index date) or (2) 1 such claim <or=14 days before the index date. Persons who were not continuously eligible for medical and drug benefits for 6 months before and after the index date (pretreatment and follow-up, respectively) were dropped from the study sample. Use of opioids, including both short- and long-acting formulations, was compared between pretreatment and follow-up. Patients were stratified in the study analyses by whether they received 1 or >or=2 prescriptions for gabapentin.

RESULTS

Forty-five patients with PHN began therapy with gabapentin during the period of interest; 35 (77.8%) received >or=2 prescriptions for gabapentin. The proportion of patients receiving opioids decreased significantly between pretreatment and follow-up (from 88.9% to 71.1%; P = 0.03); the mean number of opioid prescriptions per patient also decreased significantly (from 3.9 to 3.0; P = 0.03). These reductions were observed only in patients who received >or=2 prescriptions for gabapentin; there was no significant change in opioid use among those who received only 1 prescription for gabapentin.

CONCLUSION

In this study, initiation of gabapentin therapy in patients with PHN was associated with a reduction in the use of opioid analgesics.

Use of gabapentin to reduce chronic neuropathic pain in Fabry disease

The effect of the anticonvulsant gabapentin on neuropathic pain was studied in six male patients with Fabry disease, aged 15-45 years. After 4 weeks of treatment, pain, as measured using the Brief Pain Inventory, was decreased compared with baseline. Treatment was generally well tolerated. This study indicates that gabapentin should be considered as a treatment option for the neuropathic pain of Fabry disease.

Postnatally induced differences in adult pain sensitivity depend on genetics, gender and specific experiences: reversal of maternal deprivation effects by additional postnatal tactile stimulation or chronic imipramine treatment

Postnatal endotoxin exposure, handling or maternal deprivation produce long-lasting individual differences in various neuroendocrine and behavioural responses. However, the impact of postnatal experiences on adult pain sensitivity and its reversibility by postnatal additional tactile stimulation or antidepressants in adulthood is not well understood. Therefore, postnatal endotoxin application as a model for infection, maternal deprivation as a model for depression, and postnatal handling as a model for stimulation were compared with respect to the effects on pain sensitivity in adult Fischer 344 (F344) and Lewis (LEW) rats. Handling increased hot plate latencies in adult F344 and LEW rats, while maternal deprivation shortened hot plate latencies only in LEW rats. Prophylactic treatment strategies, such as tactile stimulation of the dorsal neck region of pups directly after maternal deprivation, or chronic treatment of adult maternally deprived rats using imipramine, successfully provide protection against the maternal deprivation-induced shortening of hot plate latencies. Thus, there is considerable specificity of certain postnatal experiences in modulating adult pain sensitivity and the maternal deprivation-induced hyperalgesia is reversible by different interventional regimes. These findings may explain some of the individual differences in pain sensitivity of humans and the differential efficacy of antidepressants in pain syndromes.

Life after shingles: the management of postherpetic neuralgia

Chronic pain may have devastating effects on the physical and psychological well being of many patients (Harden, 1999). Most community nurses are in contact with a number of patients with chronic pain and will be asked for advice and recommendations with regards to its management. Chronic neuropathic pain is a complex and sometimes intractable condition that patients will seek help for, from either GPs or from the community nursing teams. This article will examine one neuropathic pain syndrome - post-herpetic neuralgia - and review the evidence base in relation to treatment strategies, in an attempt to support community staff in the management of this difficult to treat pain syndrome.

Drug interactions with patient-controlled analgesia

Patient-controlled analgesia (PCA) has become standard procedure in the clinical treatment of pain. Its widespread use in patients with all kinds of diseases opens a variety of possible interactions between analgesics used for PCA and other drugs that might be administered concomitantly to the patient. Many of these drug interactions are of little clinical importance. However, some drug interactions have been reported to result in serious clinical problems. Drug interactions can either predominantly affect the pharmacokinetics or pharmacodynamics of the drug. Most important pharmacokinetic drug interactions occur at the level of drug metabolism or protein binding. Acceleration of methadone metabolism caused by cytochrome P450 (CYP) 3A4 induction by antiretroviral drugs or rifampicin (rifampin) has caused methadone withdrawal symptoms. Lack of morphine formation from codeine as a result of CYP2D6 inhibition by quinidine results in an almost complete loss of the analgesic effects of codeine. Alterations of methadone protein binding caused by an inhibition of alpha1-acid glycoprotein synthesis by alkylating substances are another possibility for predominantly pharmacokinetically based drug interactions during PCA. Furthermore, inhibition of P-glycoprotein by anticancer drugs could result in altered transmembrane transport of morphine, methadone or fentanyl, although this has not been shown to be of clinical relevance. Synergistic effects of systemically administered opioids with spinally or topically delivered opioids or anaesthetics have been reported frequently. The same is true for the opioid-sparing effects of coadministered non-opioid analgesics. Antidepressants, anticonvulsants or alpha2-adrenoreceptor agonists have also been shown to exert additive analgesic effects when administered together with an opioid. Inconsistent findings, however, are reported regarding the treatment of patients with opioid-induced nausea and sedation, since coadministration of antiemetics either increased or decreased the respective adverse effects or revealed additional unwanted drug effects.