Systemic lidocaine for neuropathic pain relief

Management of itch in atopic dermatitis

Atopic dermatitis is a common, pruritic, inflammatory skin disorder. Chronic, localized, or even generalized pruritus is the diagnostic hallmark of atopic dermatitis, and its management remains a challenge for physicians. The threshold for itch and alloknesis is markedly reduced in these patients, and infections can promote exacerbation and thereby increase the itch. Modern management consists of anti-inflammatory, occasionally antiseptic, as well as antipruritic therapies to address the epidermal barrier as well as immunomodulation or infection. Mild forms of atopic dermatitis may be controlled with topical therapies, but moderate-to-severe forms often require a combination of systemic treatments consisting of antipruritic and immunosuppressive drugs, phototherapy, and topical compounds. In addition, patient education and a therapeutic regimen to help the patient cope with the itch and eczema are important adjuvant strategies for optimized long-term management. This review highlights various topical, systemic, and complementary and alternative therapies, as well as provide a therapeutic ladder for optimized long-term control of itch in atopic dermatitis.

Stable Expression and Characterization of Human PN1 and PN3 Sodium Channels

Nociceptive transduction in inflammatory and neuropathic pain involves peripherally expressed voltage-gated sodium channels, such as tetrodotoxin (TTX)-sensitive PN1 and TTX-resistant PN3. We generated recombinant cell lines stably expressing the human PN1 and PN3 sodium channels in Chinese hamster ovary (CHO) cells using inducible expression vectors. The PN1 and PN3 cDNAs were isolated from human adrenal gland and heart poly(A)+ RNAs, respectively. The recombinant human PN1 currents exhibited rapid activation and inactivation kinetics and were blocked by TTX with a half-maximal inhibitory concentration (IC50) of 32.6 nM. The human PN3 channel expressed in stable transfectants showed TTX-resistant inward currents with slow inactivation kinetics. The IC50 value for TTX was 73.3 microM. The voltage-dependence of activation of the PN3 channel was shifted to the depolarizing direction, compared to that of the PN1 channel. Lidocaine and mexiletine exhibited tonic and use-dependent block of PN1 and PN3 channels. The PN1 channel was more susceptible to inhibition by mexiletine than PN3. These results suggest that stable transfectants expressing the human PN1 and PN3 sodium channels will be useful tools to define subtype selectivity for sodium channel blockers.

A randomized, controlled, double-blind trial of fluoroscopic caudal epidural injections in the treatment of lumbar disc herniation and radiculitis

STUDY DESIGN

A randomized, controlled, double-blind trial.

OBJECTIVE

To assess the effectiveness of fluoroscopically directed caudal epidural injections in managing chronic low back and lower extremity pain in patients with disc herniation and radiculitis with local anesthetic with or without steroids.

SUMMARY OF BACKGROUND DATA

The available literature on the effectiveness of epidural injections in managing chronic low back pain secondary to disc herniation is highly variable.

METHODS

One hundred twenty patients suffering with low back and lower extremity pain with disc herniation and radiculitis were randomized to one of the two groups: group I received caudal epidural injections with an injection of local anesthetic, lidocaine 0.5%, 10 mL; group II patients received caudal epidural injections with 0.5% lidocaine, 9 mL, mixed with 1 mL of steroid. The Numeric Rating Scale (NRS), the Oswestry Disability Index 2.0 (ODI), employment status, and opioid intake were utilized with assessment at 3, 6, and 12 months posttreatment.

RESULTS

The percentage of patients with significant pain relief of 50% or greater and/or improvement in functional status with 50% or more reduction in ODI scores was seen in 70% and 67% in group I and 77% and 75% in group II with average procedures per year of 3.8 ± 1.4 in group I and 3.6 + 1.1 in group II. However, the relief with first and second procedures was significantly higher in the steroid group. The number of injections performed was also higher in local anesthetic group even though overall relief was without any significant difference among the groups. There was no difference among the patients receiving steroids.

CONCLUSION

Caudal epidural injection with local anesthetic with or without steroids might be effective in patients with disc herniation or radiculitis. The present evidence illustrates potential superiority of steroids compared with local anesthetic at 1-year follow-up.

Comparison of actions of systemically and locally administrated local anaesthetics in diabetic rats with painful neuropathy

Nothing is known about actions of levobupivacaine, a long-acting local anaesthetic belonging to the amino amide group, in diabetes-induced neuropathic pain conditions. In this study, we therefore investigated the possible antihyperalgesic and antiallodynic effects of levobupivacaine in diabetic animal model. Actions of systemically (intraperitoneal) or locally (intraplantar) administrated levobupivacaine on streptozotocin-induced diabetic rats with painful neuropathy were examined using a thermal plantar test and a dynamic plantar aesthesiometer. Effects of levobupivacaine were compared with those of a well-known amide local anaesthetic lidocaine. Levobupivacaine was more potent than lidocaine in all tests employed on diabetic rats. After intraperitoneal injections to diabetic rats, levobupivacaine, but not lidocaine, produced pronounced antihyperalgesic and antiallodynic effects. However, intraplantar administration of both levobupivacaine and lidocaine produced antihyperalgesic and antiallodynic action in diabetic rats. In contrast to the transient effects of lidocaine (30 min), antihyperalgesic and antiallodynic actions of levobupivacaine gradually disappeared within 120 min after intraplantar injections. Intraperitoneal or intraplantar administrations of levobupivacaine or lidocaine at the effective dose had no effect on any parameters in intact rats. Findings revealed that antiallodynic and antihyperalgesic potency of levobupivacaine was higher in comparison with that of lidocaine after their intraperitoneal or intraplantar administration to diabetic animals. Furthermore, locally administrated levobupivacaine has the greatest antihyperalgesic and antiallodynic actions in diabetic rats.

Transforaminal injection of corticosteroids for lumbar radiculopathy: systematic review and meta-analysis

BACKGROUND

Transforaminal epidural injection of steroids is used to treat lumbar radicular pain. However, there are only a few well-designed randomized, controlled studies on the effectiveness of steroid injection.

STUDY DESIGN

Hence, this study aims to assess the effectiveness of steroid injection to treat lumbar radicular pain using a meta-analysis of transforaminal epidural injection therapy for low back and lumbar radicular pain. The comparison was based on the mean difference in the Visual Analogue Score (VAS) and Oswestry Disability Index (ODI) from baseline to the specified followed up.

METHODS

The available literature of lumbar transforaminal epidural injections in managing low back and radicular pain was reviewed. Data sources included relevant literature of the English language identified through searches of PubMed and EMBASE from 1966 to 2009, and manual searches of the bibliographies of known primary and review articles. Finally, the search included the Current Controlled Trials Register and the Cochrane Database of Controlled Trials.

RESULTS

The initial search identified 126 papers. After screening, five randomised controlled trials (RCTs) were studied for analysis and only three of these had followed-up patients systematically with pain and disability outcome scores to 3 months and of these, only one had follow up to 12 months. A total of 187 patients ('treatment group' receiving local anaesthetic/steroid injection) were compared with 181 patients ('control' group, receiving local anaesthetic only or saline injection). Improvement in pain (standardised mean difference in VAS 0.2 in favour of 'treatment'; 95%CI: -0.41 to 0.00, p = 0.05, I squared 0%) but not disability (standardised mean difference in ODI 0; 95%CI: -0.21 to 0.20, p = 0.99, I squared 0%) was observed between 'treatment' and 'control' groups; these differences were not significant. Additionally, the one study following patients to 12 months did not find any significant difference in VAS and ODI between treatment and control groups.

CONCLUSION

The current meta-analysis shows that transforaminal epidural steroid injections, when appropriately performed, should result in an improvement in pain, but not disability. The three RCTs that followed patients to 3 months (and the single study to 12 months) have found no benefit by the addition of steroids. The limitations of this study include the paucity of the available literature.

Combination drug therapy for chronic pain: a call for more clinical studies

Chronic pain is a debilitating clinical condition associated with a variety of disease entities including diabetic neuropathy, postherpetic neuralgia, low back pathology, fibromyalgia, and neurological disorders. For many general practitioners and specialists, managing chronic pain has become a daunting challenge. As a modality of multidisciplinary chronic pain management, medications are often prescribed in combinations, an approach referred to as combination drug therapy (CDT). However, many medications for pain therapy, including antidepressants and opioid analgesics, have significant side effects that can compound when used in combination and impact the effectiveness of CDT. To date, clinical practice of CDT for chronic pain has been based largely on clinical experiences. In this article, we will focus on (1) the scientific basis and rationales for CDT, (2) current clinical data on CDT, and (3) the need for more clinical studies to establish a framework for the use of CDT.

PERSPECTIVE

More preclinical, clinical, and translational studies are needed to improve the efficacy of combination drug therapy that is an integral part of a comprehensive approach to the management of chronic pain.

Is Epidural Analgesia Necessary after Video-Assisted Thoracoscopic Lobectomy?

Most studies have shown that thoracic epidural analgesia reduces postoperative pain, but it carries potential risks. Recently, video-assisted thoracoscopic surgery has become an established technique that causes minimal postoperative pain. This report shows that thoracic epidural analgesia is not always necessary after video-assisted thoracoscopic lobectomy. From January to December 2007, 30 consecutive patients who underwent video-assisted thoracoscopic lobectomy were examined retrospectively. We analyzed the necessity for routine thoracic epidural analgesia. The continuous subcutaneous analgesia catheter for morphine (2 mg in 48 h) was removed from 15 patients on postoperative day 1, and from the other 15 on day 2. We administered loxoprofen sodium hydrate, diclofenac sodium suppository, pentazocine hydrochloride, and mexiletine hydrochloride for postoperative analgesia, as needed. The mean pain score was no more than 1.0. The maximum score was 3.0 on day 0, and 2.0 on day 14; subsequently, no pain score exceeded 2.0. The postoperative hospital stay was 8.7 ± 0.8 days. All patients made uneventful postoperative recoveries. There is no need for thoracic epidural analgesia after every video-assisted thoracoscopic lobectomy because our patients recovered with no serious complication. Less invasive surgical approaches should require simpler postoperative pain management.

Proctalgia fugax, an evidence-based management pathway

PURPOSE

Proctalgia fugax (PF) is a benign anorectal condition which has been described in the literature since the nineteenth century commonly presenting to general surgeons. There is little high level evidence on the subject and its therapeutic modalities. We aimed through this systematic literature review to outline the definition and diagnostic criteria of this condition, the aetiology and differential diagnoses and describe the different treatment modalities that have been attempted and their success.

METHOD

A literature search of Google Scholar and Medline using Pubmed as the search engine was used to identify all studies directly related to the definition, aetiology and treatment options for this condition (latest at 12 August 2008) was performed.

RESULTS

The search produced 61 references with three others obtained from the references of these papers. The prevalence of PF in the general population ranges from 4% to 18%. The diagnosis is based on the presence of characteristic symptoms as defined by Rome III guidelines and physical examination. The mainstay of treatment is reassurance and careful counselling with evidence in the literature for warm baths, topical treatment with glyceryl trinitrate or diltiazem and salbutamol inhalation. In persistent cases, local anaesthetic blocks, clonidine or Botox injections can be considered after clarification of risk and benefit.

CONCLUSION

Based on this we suggest that diagnosis should be made through exclusion of common organic causes such as haemorrhoids, anal fissure or anorectal carcinoma and on the fulfillment of Rome III criteria. The main treatment for this benign condition remains reassurance and topical treatment.

Intravenous lidocaine and mexiletine in the management of trigeminal autonomic cephalalgias

Lidocaine and mexiletine are class 1B antiarrhythmic drugs that act on sodium channels. Lidocaine is also an important anesthetic and topical agent that is useful in the treatment of multiple pain disorders, and mexiletine is commonly used for neuropathic pain and myotonia. Both intravenous lidocaine and mexiletine are increasingly used to treat pain syndromes and appear to be particularly effective in neuropathic pain. This suggests a role for these agents in patients with headache disorders. This article describes the role of intravenous lidocaine and mexiletine in the management of headache and trigeminal autonomic cephalalgias based on the published literature to date and provides practical guidelines for their use.

Neuropathic pain management in chronic laminitis

Managing pain in horses afflicted by chronic laminitis is one of the greatest challenges in equine clinical practice because it is the dreadful suffering of the animals that most often forces the veterinarian to end the battle with this disease. The purpose of this review is to summarize our current understanding of the complex mechanisms involved in generating and amplifying pain in animals with laminitis and, based on this information, to propose a modified approach to pain therapy. Furthermore, a recently developed pain scoring technique is presented that may help better quantify pain and the monitoring of responses to analgesic treatment in horses with laminitis.

A role for intravenous lidocaine in severe cancer-related neuropathic pain at the end-of-life

BACKGROUND

Systemic administration of lidocaine has been widely reported to provide effective analgesia in both cancer and non-malignant pain.

CASE REPORT

We report the use of intravenous lidocaine in the management of cancer-related neuropathic pain and its pivotal role in restoring function and facilitating end-of-life care at home.

Pain quality predicts lidocaine analgesia among patients with suspected neuropathic pain

OBJECTIVE

Oral sodium channel blockers have shown mixed results in randomized controlled trials despite the known importance of sodium channels in generating pain. We hypothesized that differing baseline pain qualities (e.g. "stabbing" vs "dull") might define specific subgroups responsive to intravenous (IV) lidocaine-a potent sodium channel blocker.

DESIGN

A prospective cohort study of 71 patient with chronic pain suspected of being neuropathic were recruited between January 2003 and July 2007 and underwent lidocaine infusions at Stanford University Hospital in a single-blind nonrandomized fashion. Baseline sensory pain qualities were measured with the Short-Form McGill Pain Questionnaire (SF-MPQ). Pain intensity was measured with a visual analog scale (VAS).

RESULTS

Factor analysis demonstrated two underlying pain quality factors among SF-MPQ sensory items: a heavy pain and a stabbing pain. Baseline heavy pain quality, but not stabbing quality predicted subsequent relief of pain intensity in response to lidocaine. In contrast, these factors did not predict divergent analgesic responses to placebo infusions. In response to each 1 mcg/mL increase in lidocaine plasma level, patients with high heavy pain quality drop their VAS 0.24 (95% CI 0.05-0.43) more points than those with low heavy pain quality (P < 0.013).

CONCLUSIONS

"Heavy" pain quality may indentify patients with enhanced lidocaine responsiveness. Pain quality may identify subgroups among patients with suspected neuropathic pain responsive to IV lidocaine. Further investigation is warranted to validate and extend these findings.

Effect of systemic lidocaine on visceral and somatic nociception in conscious horses

REASONS FOR PERFORMING STUDY

Commonly used analgesics (nonsteroidal anti-inflammatory agents, opioids and alpha2-agonists) have unwanted side effects. An effective alternative with minimal adverse effects would benefit clinical equine pain management.

OBJECTIVES

To compare the effect of lidocaine or saline on duodenal and rectal distension threshold pressure and somatic thermal threshold in conscious mature horses.

HYPOTHESIS

Systemically administered lidocaine would increase somatic and visceral nociceptive thresholds.

METHODS

Lidocaine (2 mg/kg bwt bolus followed by 50 microg/kg bwt/min for 2 h) or saline was administered to 6 horses each carrying a permanently implanted gastric cannula, in a randomised, blinded cross-over design. Thermal threshold was measured using a probe containing a heater element placed over the withers which supplied heat until the horse responded. A barostatically controlled intraduodenal balloon was distended until a discomfort response was obtained. A rectal balloon was inflated until extruded or signs of discomfort noted.

RESULTS

Thermal threshold was increased significantly 30 and 90 mins after the start of lidocaine infusion. There was no change in duodenal distension pressure and a small but clinically insignificant change in colorectal distension pressure in the lidocaine group.

CONCLUSIONS

At the dose used, systemically administered lidocaine produced thermal antinociception but minimal changes in visceral nociception.

POTENTIAL RELEVANCE

At these doses, lidocaine may play a role in somatic analgesia in horses.

Preemptive analgesic effect of lidocaine in a chronic neuropathic pain model

Preemptive analgesia inhibits the progression of pain caused by surgical lesions. To analyze the effect of lidocaine on postoperative pain relief, we performed compression of the right sciatic nerve in Wistar rats and observed the differences on behavior between the group that received lidocaine and the group that was not treated with the local anesthetics pre-operatively. Group 1 was not operated (control); group 2 underwent the sciatic nerve ligature without lidocaine; group 3, underwent surgery with previous local infiltration of lidocaine. Group 2 showed significantly longer scratching times with a peak on day 14 post-operative (p=0.0005) and reduction in the latency to both noxious (p=0.003) and non-noxious (p=0.004) thermal stimulus. Group 3 presented significantly shorter scratching times (p=0.004) and longer latency times when compared to Group 2. Preemptive use of lidocaine 2% can potentially reduce the postoperative neuropathic pain associated with sciatic nerve compression.

Management of neuropathic pain after surgical and non-surgical trauma with lidocaine 5% patches: study of 40 consecutive cases

OBJECTIVE

To determine the efficacy of lidocaine 5% patches [Versatis, commercialised by Grünenthal GmbH, Aachen, Germany] in patients with PNCCP.

BACKGROUND

This study focuses on chronic pain states of a neuropathic nature, located at the scar or over a larger area of the skin around the scar. This post-operative/post-traumatic neuropathic chronic cutaneous pain (PNCCP) may be a side-effect of any incision of the skin in the context of a surgical procedure or a traumatic event.

RESEARCH DESIGN AND METHODS

A single-centre, open, non-randomised, prospective study was performed in a university hospital referral centre for patients with chronic neuropathic pain after surgical or non-surgical trauma. Forty consecutive patients with chronic PNCCP, a VAS score > or =5, a LANSS score > or =12, and a stable consumption of pain medication were prospectively evaluated. All patients were given lidocaine 5% patches, following a 12 h on/off schedule.

MAIN OUTCOME MEASURES

Visual analogue scale (VAS) and the Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) scorings were performed pretreatment (day 0), on the 28th day (4 weeks), and after 84 days (12 weeks).

RESULTS

The mean pretreatment VAS score (VAS(0)) was 7.225 +/- 1.209, and the mean pretreatment LANSS score (LANSS(0)) was 18.60 +/- 2.610. The number of patients with a VAS score <5 at the latest follow-up (VAS(84)) was 21 (52.5%). Mean VAS(84) was 4.625 +/- 1.675. Seventeen patients (42.5%) had a LANSS score <12 at the latest follow-up. Overall mean LANSS(84) was 12.85 +/- 3.093.

CONCLUSION

Lidocaine 5% patches seem to be an effective treatment of post-surgical and post-traumatic pain. These results should be supported with randomised and placebo-controlled studies with larger sample sizes and longer follow-ups.

Lidocaine prevents referred hyperalgesia associated with cystitis

AIMS

Lidocaine produces analgesia by inhibiting excitation of nerve endings or blocking impulse conduction in peripheral nerves. This study was performed to determine whether intrathecal or intravesical administration of lidocaine prior, or subsequent, to induction of chemical cystitis in rats would block referred mechanical hyperalgesia.

METHODS

Intrathecal or intravesical lidocaine was administered 15 (intrathecal) or 30 (intravesical) min before intravesical instillation of saline or 1 mM acrolein (400 microl) or 4 hr after saline or acrolein instillation in female Wistar rats. Mechanical sensitivity of hind paws was determined at 24 hr prior to any treatment (baseline) and, 4, 24, and 48 hr after intravesical instillation of acrolein or saline. Also, nerve growth factor (NGF) content was measured in bladder and dorsal root ganglia (DRG).

RESULTS

Pre-treatment with intrathecal or intravesical lidocaine attenuated acrolein-induced referred mechanical hyperalgesia of the hind paws. Lidocaine administered after acrolein instillation did not alter referred hyperalgesia. Lidocaine treatment prior to or after induction of cystitis reduced NGF content in the bladder.

CONCLUSIONS

These results indicate that pre-treatment with lidocaine attenuates referred hyperalgesia associated with cystitis. Lidocaine treatment 4 hr after induction of cystitis failed to prevent referred hyperalgesia despite a similar decrease in bladder NGF. Neurourol. Urodynam. (c) 2009 Wiley-Liss, Inc.

Translational pain research: achievements and challenges

The achievements in both preclinical and clinical pain research over the past 4 decades have led to significant progress in clinical pain management. However, pain research still faces enormous challenges and there remain many obstacles in the treatment of clinical pain, particularly chronic pain. Translational pain research needs to involve a number of important areas including: 1) bridging the gap between pain research and clinical pain management; 2) developing objective pain-assessment tools; 3) analyzing current theories of pain mechanisms and their relevance to clinical pain; 4) exploring new tools for both preclinical and clinical pain research; and 5) coordinating research efforts among basic scientists, clinical investigators, and pain-medicine practitioners. These issues are discussed in this article in light of the achievements and challenges of translational pain research.

PERSPECTIVE

The subjective nature of clinical pain calls for innovative research approaches. As translational pain research emerges as an important field in pain medicine, it will play a unique role in improving clinical pain management through coordinated bidirectional research approaches between bedside and bench.

A combined effect of dextromethorphan and melatonin on neuropathic pain behavior in rats

Previous study has shown that administration of melatonin into the anterior cingulate cortex contralateral to peripheral nerve injury prevented exacerbation of mechanical allodynia with a concurrent improvement of depression-like behavior in Wistar-Kyoto (WKY) rats, a genetic variation of Wistar rats. In the present study, we examined the effect of the individual versus combined treatment of melatonin and/or dextromethorphan (DM), a clinically available N-methyl-d-aspartate (NMDA) receptor antagonist, on pain behaviors in WKY rats with chronic constriction sciatic nerve injury (CCI). Pain behaviors (thermal hyperalgesia and mechanical allodynia) were established at one week after CCI. WKY rats were then treated intraperitoneally with various doses of melatonin, DM or their combination once daily for the following week. At the end of this one-week treatment, behavioral tests were repeated in these same rats. While DM alone was effective in reducing thermal hyperalgesia at three tested doses (15, 30 or 60 mg/kg), it reduced mechanical allodynia only at high doses (30 or 60 mg/kg). By comparison, administration of melatonin alone was effective in reducing thermal hyperalgesia only at the highest dose (120 mg/kg, but not 30 or 60 mg/kg) tested in this experiment. Melatonin alone failed to reverse allodynia at all three tested doses (30, 60 and 120 mg/kg). However, the combined intraperitoneal administration of melatonin (30 mg/kg) and DM (15 mg/kg) effectively reversed both thermal hyperalgesia and mechanical allodynia although each individual dose alone did not reduce pain behaviors. These results suggest that a combination of melatonin with a clinically available NMDA receptor antagonist might be more effective than either drug alone for the treatment of neuropathic pain.

Neuropsychiatric Side-Effects of Lidocaine: Examples from the Treatment of Headache and a Review

Lidocaine has been used in treatment of patients with refractory headache. Personal observations of neuropsychiatric toxicity in these patients led us to review our cases and the literature systematically for lidocaine side-effects, especially neuropsychiatric symptoms. In our series of 20 patients, side-effects were observed in all, the most frequent being neuropsychiatric (75%) and cardiological (50%). When reviewing published series on intravenous lidocaine use, reports of side-effects range from 0 to 100%, with neuropsychiatric symptoms being reported in 1.8–100%. Thirty-six case reports of lidocaine-induced psychiatric symptoms were also analysed. Psychiatric symptoms of toxicity were similar in most patients, despite their differing ages, pathologies, co-therapies and lidocaine dosages. In conclusion, lidocaine neuropsychiatric toxicity has a well-recognized stereotypical clinical presentation that is probably unrecognized in headache series. As lidocaine represents an emerging alternative therapy in headache, particularly in short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing, clinicians and patients should be aware of the extent of this problem.

Intravenous lidocaine in the treatment of refractory headache: a retrospective case series

BACKGROUND

New treatments are needed to treat chronic daily headache (CDH) and chronic cluster headache (CCH). New treatments are needed to treat this population and intravenous (IV) lidocaine is a novel treatment for CDH.

OBJECTIVE

The aim of this study was to examine the use of IV lidocaine for refractory CDH patients in an inpatient setting.

METHODS

This was an open-label, retrospective, uncontrolled study of IV lidocaine for 68 intractable headache patients in an inpatient setting. We reviewed the medical records of patients receiving IV lidocaine between February 6, 2003 and June 29, 2005.

RESULTS

Pretreatment headache scores averaged 7.9 on an 11-point scale and posttreatment scores averaged 3.9 representing an average change of 4. Average length of treatment was 8.5 days. Lidocaine infusion was generally well tolerated with a low incidence of adverse events leading to discontinuation of treatment.

CONCLUSIONS

This study suggests benefit of lidocaine treatment and the need for further prospective analyses. The mechanism of lidocaine in treating headache is unknown.

Neuropathic pain in dogs and cats: if only they could tell us if they hurt

Neuropathic pain is difficult to diagnose in veterinary patients because they are unable to verbalize their pain. By assuming that neuropathic pain may exist based on the history of events that each patient has experienced, a focused client history and neurologic examination may identify a lesion resulting in persistent or spontaneous pain. Once neuropathic pain is diagnosed, a trial analgesic or acupuncture session(s) should be prescribed with instructions for owners to observe behavior. Dosing of the analgesic can be titrated to the patient's needs while avoiding adverse effects. When a particular analgesic may be ineffectual, an alternate class should be tried. As research into the neurobiologic mechanisms of neuropathic pain continues, specific therapies for its management should eventually appear in the human clinical setting and subsequently be investigated for veterinary clinical use.

The effect of intravenous lidocaine on brain activation during non-noxious and acute noxious stimulation of the forepaw: a functional magnetic resonance imaging study in the rat

BACKGROUND

Lidocaine can alleviate acute as well as chronic neuropathic pain at very low plasma concentrations in humans and laboratory animals. The mechanism(s) underlying lidocaine's analgesic effect when administered systemically is poorly understood but clearly not related to interruption of peripheral nerve conduction. Other targets for lidocaine's analgesic action(s) have been suggested, including sodium channels and other receptor sites in the central rather than peripheral nervous system. To our knowledge, the effect of lidocaine on the brain's functional response to pain has never been investigated. Here, we therefore characterized the effect of systemic lidocaine on the brain's response to innocuous and acute noxious stimulation in the rat using functional magnetic resonance imaging (fMRI).

METHODS

Alpha-chloralose anesthetized rats underwent fMRI to quantify brain activation patterns in response to innocuous and noxious forepaw stimulation before and after IV administration of lidocaine.

RESULTS

Innocuous forepaw stimulation elicited brain activation only in the contralateral primary somatosensory (S1) cortex. Acute noxious forepaw stimulation induced activation in additional brain areas associated with pain perception, including the secondary somatosensory cortex (S2), thalamus, insula and limbic regions. Lidocaine administered at IV doses of either 1 mg/kg, 4 mg/kg or 10 mg/kg did not abolish or diminish brain activation in response to innocuous or noxious stimulation. In fact, IV doses of 4 mg/kg and 10 mg/kg lidocaine enhanced S1 and S2 responses to acute nociceptive stimulation, increasing the activated cortical volume by 50%-60%.

CONCLUSION

The analgesic action of systemic lidocaine in acute pain is not reflected in a straightforward interruption of pain-induced fMRI brain activation as has been observed with opioids. The enhancement of cortical fMRI responses to acute pain by lidocaine observed here has also been reported for cocaine. We recently showed that both lidocaine and cocaine increased intracellular calcium concentrations in cortex, suggesting that this pharmacological effect could account for the enhanced sensitivity to somatosensory stimulation. As our model only measured physiological acute pain, it will be important to also test the response of these same pathways to lidocaine in a model of neuropathic pain to further investigate lidocaine's analgesic mechanism of action.

Injury discharges regulate calcium channel alpha-2-delta-1 subunit upregulation in the dorsal horn that contributes to initiation of neuropathic pain

Previous studies have shown that peripheral nerve injury in rats induces increased expression of the voltage gated calcium channel (VGCC) alpha-2-delta-1 subunit (Ca v alpha2 delta1) in spinal dorsal horn and sensory neurons in dorsal root ganglia (DRG) that correlates to established neuropathic pain states. To determine if injury discharges trigger Ca v alpha2 delta1 induction that contributes to neuropathic pain initiation, we examined allodynia onset and Ca v alpha2 delta1 levels in DRG and spinal dorsal horn of spinal nerve ligated rats after blocking injury induced neural activity with a local brief application of lidocaine on spinal nerves before the ligation. The lidocaine pretreatment blocked ligation-induced discharges in a dose-dependent manner. Similar pretreatment with the effective concentration of lidocaine diminished injury-induced increases of the Ca v alpha2 delta1 in DRG and abolished that in spinal dorsal horn specifically, and resulted in a delayed onset of tactile allodynia post-injury. Both dorsal horn Ca v alpha2 delta1 upregulation and tactile allodynia in the lidocaine pretreated rats returned to levels similar to that in saline pretreated controls 2 weeks post the ligation injury. In addition, preemptive intrathecal Ca v alpha2 delta1 antisense treatments blocked concurrently injury-induced allodynia onset and Ca v alpha2 delta1 upregulation in dorsal spinal cord. These findings indicate that injury induced discharges regulate Ca v alpha2 delta1 expression in the spinal dorsal horn that is critical for neuropathic allodynia initiation. Thus, preemptive blockade of injury-induced neural activity or Ca v alpha2 delta1 upregulation may be a beneficial option in neuropathic pain management.

[New substances and applications for postoperative pain therapy]

The onset of postoperative pain is the result of various pathophysiological mechanisms and depends on the type of surgery performed. Therefore, any adequate postoperative pain treatment requires multimodal and procedure-specific analgesia. In addition to reducing perioperative complications and improving patient comfort, optimal postoperative pain management also represents an important quality characteristic which can influence the patient in their choice of hospital. In the past 1-2 years, known groups of substances have been rediscovered for postoperative pain therapy (e.g., Gabapentin and Pregabalin, i.v. Lidocaine, Ketamine or glucocorticoids), while new substances (coxibe, oral oxycodone+naloxone) and applications have been developed. The present overview article discusses the advantages and disadvantages of these substances and analgesic methods, as well as their specific areas of application.

Tolperisone: a typical representative of a class of centrally acting muscle relaxants with less sedative side effects

Tolperisone, a piperidine derivative, is assigned to the group of centrally acting muscle relaxants and has been in clinical use now for decades. The review summarizes the known pharmacokinetics, pharmacodynamics, toxicology and side effects in humans and the clinical use of tolperisone. A future perspective for further exploration of this drug is given.

Morphine versus mexiletine for treatment of postamputation pain: a randomized, placebo-controlled, crossover trial

BACKGROUND

Stump and phantom pains are debilitating sequelae of amputations that are often resistant to treatment. The efficacy of pharmacologic therapies, including opioids and sodium channel blockers, for postamputation pain is uncertain.

METHODS

The authors conducted a double-blind, randomized, placebo-controlled, crossover study in adult patients with postamputation pain of 6 months or longer and greater than 3 on a 0-10 numeric pain rating scale. Each of the three treatment periods (morphine, mexiletine, or placebo) included a 1-week drug-free interval followed by 4-week titration, 2-week maintenance, and 2-week drug-taper phases. The primary outcome measure was change in average pain intensity from the drug-free baseline to the last week of maintenance.

RESULTS

Sixty amputees were enrolled; data were analyzed from 56 subjects for one drug period, 45 subjects for two drug periods, and 35 subjects who completed all three drug periods. The mean morphine and mexiletine dosages were 112 and 933 mg, respectively. Morphine treatment provided lower pain scores compared with placebo and mexiletine (P = 0.0003). The mean percent pain relief during treatment with placebo, mexiletine, and morphine was 19, 30, and 53%, respectively (P < 0.0001, morphine vs. placebo and mexiletine). The numbers needed to treat to obtain 50% and 33% decreases in pain intensity with morphine were 5.6 and 4.5, respectively. Treatment with morphine was associated with a higher rate of side effects.

CONCLUSIONS

Therapy with morphine, but not mexiletine, resulted in a decrease in intensity of postamputation pain but was associated with a higher rate of side effects and no improvement in self-reported levels of overall functional activity and pain-related interference in daily activities.

Cervical medial branch blocks for chronic cervical facet joint pain: a randomized, double-blind, controlled trial with one-year follow-up

STUDY DESIGN

A double-blind, randomized, controlled trial.

OBJECTIVE

To determine the clinical effectiveness of therapeutic local anesthetic cervical medial branch blocks with or without steroid in managing chronic neck pain of facet joint origin.

SUMMARY OF BACKGROUND DATA

The prevalence of persistent neck pain, secondary to involvement of cervical facet or zygapophysial joints, has been described in controlled studies as varying from 39% to 67%. Intra-articular injections, medial branch nerve blocks, and neurolysis of medial branch nerves have been described in managing chronic neck pain of facet joint origin.

METHODS

A total of 120 patients were included, with 60 patients in each of the local anesthetic and steroid groups. All the patients met the diagnostic criteria of cervical facet joint pain by means of comparative, controlled diagnostic blocks, and the inclusion criteria. Group I consisted of medial branch blocks with bupivacaine. Group II consisted of cervical medial branch blocks with bupivacaine and steroid. Numerical pain scores, Neck Disability Index, opioid intake, and work status were evaluated at baseline, 3 months, 6 months, and 12 months.

RESULTS

Significant pain relief (>or=50%) and functional status improvement was observed at 3 months, 6 months, and 12 months in over 83% of patients. The average number of treatments for 1 year was 3.5 +/- 1.0 in the nonsteroid group and 3.4 +/- 0.9 in the steroid group. Duration of average pain relief with each procedure was 14 +/- 6.9 weeks in the nonsteroid group, and it was 16 +/- 7.9 weeks in the steroid group. Significant relief and functional improvement was reported for 46 to 48 weeks in a year.

CONCLUSION

Therapeutic cervical medial branch nerve blocks, with or without steroids, may provide effective management for chronic neck pain of facet joint origin.

Dercum's disease (Lipomatosis dolorosa): successful therapy with pregabalin and manual lymphatic drainage and a current overview

Dercum's disease which is also termed lipomatosis dolorosa is a rare and relatively unknown disease. In this entity the upper arms, elbows, stomach wall, buttocks, thighs and knees are predominantly affected showing painful subcutaneous adipose tissue deposits. In addition severe hyperalgesia can be triggered by light pressure and touch. Analgesic and/or nonsteroidal antirheumatic drugs have usually only a minor or no effect. Here, we report a patient with Dercum's disease who was successfully treated with pregabalin and manual lymphatic drainage, and present a current overview of the literature.

Effects of intrathecal lidocaine on hyperalgesia and allodynia following chronic constriction injury in rats

The present study investigated the effects of different doses of intrathecal lidocaine on established thermal hyperalgesia and tactile allodynia in the chronic constriction injury model of neuropathic pain, defined the effective drug dose range, the duration of pain-relief effects, and the influence of this treatment on the body and tissues. Male Sprague-Dawley rats were divided into five groups and received intrathecal saline or lidocaine (2, 6.5, 15, and 35 mg/kg) 7 days after loose sciatic ligation. Respiratory depression and hemodynamic instability were found to become more severe as doses of lidocaine increased during intrathecal therapy. Two animals in the group receiving 35 mg/kg lidocaine developed pulmonary oedema and died. Behavioral tests indicated that 6.5, 15, and 35 mg/kg intrathecal lidocaine showed different degrees of reversal of thermal hyperalgesia, and lasted for 2-8 days, while 2 mg/kg lidocaine did not. The inhibition of tactile allodynia was only observed in rats receiving 15 and 35 mg/kg lidocaine, and the anti-allodynic effects were identical in these two groups. Histopathologic examinations on the spinal cords revealed mild changes in rats receiving 2-15 mg/kg lidocaine. However, lesions were severe after administration of 35 mg/kg lidocaine. These findings indicate that intrathecal lidocaine has prolonged therapeutic effects on established neuropathic pain. The balance between sympathetic and parasympathetic nervous activities could be well preserved in most cases, except for 35 mg/kg. Considering the ratio between useful effects and side effects, doses of 15 mg/kg are suitable for intrathecal injection for relief of neuropathic pain.

An update on the treatment of postherpetic neuralgia

Like other types of neuropathic pain, postherpetic neuralgia (PHN) can be resistant to many types of pharmacologic and interventional therapies. Although many analgesic agents have been used for the treatment of other types of neuropathic pain, tricyclic antidepressants, antiepileptic drugs, opioids, and lidocaine patch appear to demonstrate relative analgesic efficacy for the treatment of pain from PHN. There are fewer studies on the use of interventional options for the treatment of pain from PHN. The majority of interventional therapies show equivocal analgesic efficacy although some data indicate that intrathecal methylprednisolone may be effective. Further randomized, controlled trials will be needed to confirm the analgesic efficacy of analgesic and interventional therapies to determine their role in the overall treatment of patients with PHN.

PERSPECTIVE

This article reviews the analgesic options for the treatment of PHN and suggests that tricyclic antidepressants, membrane stabilizers, opioids, and lidocaine patch may demonstrate analgesic efficacy in this group of patients. These data may potentially help clinicians who attempt to provide analgesia in patients with PHN.

Current concepts of nociception: nociceptive molecular sensors in sensory neurons

PURPOSE OF REVIEW

A large number of channels that are in some way linked to sensory transduction including nociception have been discovered in recent years. This review summarizes newly discovered channels that are implicated in nociception. Furthermore, details are discussed with emphasis on their possible application to clinical use as analgesics.

RECENT FINDINGS

Studies with null mutant animals deficient in these channel genes reveal that the channels are indeed implicated in physiological as well as pathological nociception.

SUMMARY

Many transient receptor potential channels are thermosensors that detect cold, warm and hot temperatures. These channels are activated not only by natural chemicals such as capsaicin, menthol, and camphor, but by various inflammatory signaling pathways. The acid-sensing ion channel and P2X channel that detect extracellular acidosis and ATP are also implicated in some types of pain. Voltage-gated sodium or calcium channels draw attention because of their involvement in neuropathic pain.

A selective Nav1.8 sodium channel blocker, A-803467 [5-(4-chlorophenyl-N-(3,5-dimethoxyphenyl)furan-2-carboxamide], attenuates spinal neuronal activity in neuropathic rats

We have recently reported that systemic delivery of A-803467 [5-(4-chlorophenyl-N-(3,5-dimethoxyphenyl)furan-2-carboxamide], a selective Na(v)1.8 sodium channel blocker, reduces behavioral measures of chronic pain. In the current study, the effects of A-803467 on evoked and spontaneous firing of wide dynamic range (WDR) neurons were measured in uninjured and rats with spinal nerve ligations (SNLs). Administration of A-803467 (10-30 mg/kg i.v.) reduced mechanically evoked (10-g von Frey hair) and spontaneous WDR neuronal activity in SNL rats. In uninjured rats, A-803467 (20 mg/kg i.v.) transiently reduced evoked but not spontaneous firing of WDR neurons. The systemic effects of A-803467 in SNL rats were not altered by spinal transection or by systemic pretreatment with the transient receptor potential vanilloid type 1 (TRPV1) receptor agonist, resiniferatoxin, at doses that impair the function of TRPV1-expressing fibers. To determine sites of action, A-803467 was administered into spinal tissue, into the uninjured L4 dorsal root ganglion (DRG), or into the neuronal receptive field. Injections of A-803467 into the L4 DRG (30-100 nmol/1 mul) or into the hindpaw receptive field (300 nmol/50 mul) reduced evoked but not spontaneous WDR firing. In contrast, intraspinal (50-150 nmol/0.5 mul) injection of A-803467 decreased both evoked and spontaneous discharges of WDR neurons. Thus, Na(v)1.8 sodium channels on the cell bodies/axons within the L4 DRG as well as on peripheral and central terminals of primary afferent neurons regulate the inflow of low-intensity mechanical signals to spinal WDR neurons. However, Na(v)1.8 sodium channels on central terminals seem to be key to the modulation of spontaneous firing in SNL rats.