Gabapentin for neuropathic pain following spinal cord injury

Neuropathic Pain and Spinal Cord Injury: Management, Phenotypes, and Biomarkers

Chronic neuropathic pain after a spinal cord injury (SCI) continues to be a complex condition that is difficult to manage due to multiple underlying pathophysiological mechanisms and the association with psychosocial factors. Determining the individual contribution of each of these factors is currently not a realistic goal; however, focusing on the primary mechanisms may be more feasible. One approach used to uncover underlying mechanisms includes phenotyping using pain symptoms and somatosensory function. However, this approach does not consider cognitive and psychosocial mechanisms that may also significantly contribute to the pain experience and impact treatment outcomes. Indeed, clinical experience supports that a combination of self-management, non-pharmacological, and pharmacological approaches is needed to optimally manage pain in this population. This article will provide a broad updated summary integrating the clinical aspects of SCI-related neuropathic pain, potential pain mechanisms, evidence-based treatment recommendations, neuropathic pain phenotypes and brain biomarkers, psychosocial factors, and progress regarding how defining neuropathic pain phenotypes and other surrogate measures in the neuropathic pain field may lead to targeted treatments for neuropathic pain after SCI.

Central Neuropathic Pain Syndromes: Current and Emerging Pharmacological Strategies

Central neuropathic pain is caused by a disease or lesion of the brain or spinal cord. It is difficult to predict which patients will develop central pain syndromes after a central nervous system injury, but depending on the etiology, lifetime prevalence may be greater than 50%. The resulting pain is often highly distressing and difficult to treat, with no specific treatment guidelines currently available. This narrative review discusses mechanisms contributing to central neuropathic pain, and focuses on pharmacological approaches for managing common central neuropathic pain conditions such as central post-stroke pain, spinal cord injury-related pain, and multiple sclerosis-related neuropathic pain. Tricyclic antidepressants, serotonin-norepinephrine reuptake inhibitors, and gabapentinoids have some evidence for efficacy in central neuropathic pain. Medications from other pharmacologic classes may also provide pain relief, but current evidence is limited. Certain non-pharmacologic approaches, neuromodulation in particular, may be helpful in refractory cases. Emerging data suggest that modulating the primary afferent input may open new horizons for the treatment of central neuropathic pain. For most patients, effective treatment will likely require a multimodal therapy approach.

Efficacy of transcutaneous electrical nerve stimulation in people with pain after spinal cord injury: a meta-analysis

Study Design

Meta-analysis.

Objectives

This study aimed to evaluate the effect of transcutaneous electrical nerve stimulation in people with pain after spinal cord injury by meta-analysis.

Methods

Reviewed PubMed, Embase, Cochrane library, as well as China National Knowledge Infrastructure (CNKI), Wanfang, and Vip databases to search the randomized controlled trials of pain after spinal cord injury through transcutaneous electrical nerve stimulation from the beginning of the library to March 2021, and analyze the literature with RevMan 5.3 software and the bias in the literature with STATA 12.0 software.

Results

There are six randomized controlled trials in the study with 165 cases. 83 cases in the test group were given transcutaneous electrical nerve stimulation, and 82 cases in the control group used sham stimulation or other treatments. Meta-analysis results showed the experimental group’s visual analog scale (MD = −1.52, 95%CI, −2.44 to −0.60, P = 0.001) and short-form McGill pain questionnaire scores (MD = −0.70, 95% CI, −1.03 to −0.25, P = 0.002) were lower than those of the control group.

Conclusions

Transcutaneous electrical nerve stimulation has some clinical therapeutic effects on persons with pain after spinal cord injury, but due to the lack of literature, the sample size is not large, and clinical trials need to be further improved later.

Non-opioid pharmacologic treatment of chronic spinal cord injury-related pain

Purpose: Spinal cord injury-related pain is often a severe debilitating condition that adversely affects the patient's physical health, psychological wellbeing and quality of life. Opioid medications have historically been prescribed to this population with great frequency. As opioid abuse disorder becomes an ever-worsening public health issue, more attention must be placed upon non-opioid options. This paper reviews non-opioid medications to be considered when treating spinal cord injury-related pain. The pertinent literature is reviewed, and the advantages and pitfalls of various medication options are discussed in the complicated context of the individual with a spinal cord injury.Methods: Peer-reviewed journal articles and medication package insert data are reviewed.Results:. The non-opioid medications with the greatest evidence for efficacy in the treatment of chronic spinal cord injury-related pain are drawn from the antiepileptic drug and antidepressant categories though the specific selection must be nuanced to the particular individual patient. More research is required to understand the role of calcitonin, lithium, and marijuana in treating spinal cord injury-related pain.Conclusions: The complex clinical situation of each individual patient must be weighed against the risks and benefits of each medication, as reviewed in this paper, to determine the ideal treatment strategy for chronic spinal cord injury-related pain.

The CanPain SCI clinical practice guidelines for rehabilitation management of neuropathic pain after spinal cord injury: 2021 update

STUDY DESIGN

Clinical practice guidelines.

OBJECTIVES

The objective was to update the 2016 version of the Canadian clinical practice guidelines for the management of neuropathic pain in people with spinal cord injury (SCI).

SETTING

The guidelines are relevant for inpatient, outpatient and community SCI rehabilitation settings in Canada.

METHODS

The guidelines were updated in accordance with the Appraisal of Guidelines for Research and Evaluation II tool. A Steering Committee and Working Group reviewed the relevant evidence on neuropathic pain management (encompassing screening and diagnosis, treatment and models of care) after SCI. The quality of evidence was scored using Grading of Recommendations Assessment, Development and Evaluation (GRADE). A consensus process was followed to achieve agreement on recommendations and clinical considerations.

RESULTS

The working group identified and reviewed 46 additional relevant articles published since the last version of the guidelines. The panel agreed on 3 new screening and diagnosis recommendations and 8 new treatment recommendations. Two key changes to these treatment recommendations included the introduction of general treatment principles and a new treatment recommendation classification system. No new recommendations to model of care were made.

CONCLUSIONS

The CanPainSCI recommendations for the management of neuropathic pain after SCI should be used to inform practice.

Pregabalin and Gabapentin in Patients with Spinal Cord Injury-Related Neuropathic Pain: A Network Meta-Analysis

INTRODUCTION

This study was performed to explore the efficacy and safety of pregabalin and gabapentin in patients with spinal cord injury (SCI)-induced neuropathic pain to determine which treatment is most suitable for such patients.

METHODS

We searched the PubMed, MEDLINE, Embase, and Cochrane Library databases from database inception to August 31, 2020. The quality of the included studies was assessed. We selected the average pain intensity after treatment and the proportion of patients who discontinued treatment because of adverse effects as the outcome indicators for efficacy and safety, respectively. Statistical analyses were performed using Stata, v16.0, and RevMan, v5.3, software.

RESULTS

We included eight randomized controlled trials that examined four interventions (pregabalin, gabapentin, carbamazepine, and amitriptyline). Based on the average pain intensity after treatment, the efficacy order from highest to lowest was pregabalin, gabapentin, amitriptyline, carbamazepine, and placebo. Based on the proportion of patients who discontinued treatment because of adverse effects, the order from highest to lowest was pregabalin, amitriptyline, carbamazepine, gabapentin, and placebo. In addition, five studies reported the overall incidence of treatment-related adverse effects for two interventions (pregabalin and gabapentin). According to the pooled analysis of these studies, the order for the overall incidence of treatment-related adverse effects from highest to lowest was pregabalin, gabapentin, and placebo.

CONCLUSIONS

This study revealed that for patients with SCI-related neuropathic pain, pregabalin was the most effective for relieving pain, whereas gabapentin performed better in aspects associated with drug therapy-related safety.

Flumazenil therapy for a gabapentin-induced coma: a case report

Background

Spasticity and neuropathic pain are common in patients after spinal cord injury and negatively affect patients’ quality of life. Gabapentin and baclofen are frequently used to treat these conditions. We present a flumazenil-reversed gabapentin-induced coma case, which, to our knowledge, is the second one described in scientific literature.

Case presentation

A 70-year-old Caucasian man was admitted to our neurorehabilitation ward following a fall with cervical trauma that resulted in immediate tetraplegia. During his stay, he suffered from lower limb pain, both neuropathic and due to severe spasticity. Gradual baclofen and gabapentin administration was prescribed, with reduction in both pain and spasticity. One morning, the patient was found unresponsive, with a Glasgow Coma Score of 3. Head computerized tomography, electrocardiogram, electroencephalogram, vital signs, blood tests, breathing, and blood oxygenation were normal. Renal and liver failure were ruled out. Intravenous 0.25 mg of flumazenil (Anexate) was administered, resulting in complete neurocognitive recovery with a Glasgow Coma Score of 15.

Discussion and conclusions

This case report highlights the importance of the individual response to certain pharmacological agents and suggests that further studies need to be conducted both on flumazenil and gabapentin pharmacodynamics to better understand their molecular–receptor activity, and on possible multiple flumazenil mechanisms of action, beyond its classical strict benzodiazepine antagonist action.

On the therapeutic targets and pharmacological treatments for pain relief following spinal cord injury: A mechanistic review

Spinal cord injury (SCI) is globally considered as one of the most debilitating disorders, which interferes with daily activities and life of the affected patients. Despite many developments in related recognizing and treating procedures, post-SCI neuropathic pain (NP) is still a clinical challenge for clinicians with no distinct treatments. Accordingly, a comprehensive search was conducted in PubMed, Medline, Scopus, Web of Science, and national database (SID and Irandoc). The relevant articles regarding signaling pathways, therapeutic targets and pharmacotherapy of post-SCI pain were also reviewed. Data were collected with no time limitation until November 2020. The present study provides the findings on molecular mechanisms and therapeutic targets, as well as developing the critical signaling pathways to introduce novel neuroprotective treatments of post-SCI pain. From the pathophysiological mechanistic point of view, post-SCI inflammation activates the innate immune system, in which the immune cells elicit secondary injuries. So, targeting the critical signaling pathways for pain management in the SCI population has significant importance in providing new treatments. Indeed, several receptors, ion channels, excitatory neurotransmitters, enzymes, and key signaling pathways could be used as therapeutic targets, with a pivotal role of n-methyl-D-aspartate, gamma-aminobutyric acid, and inflammatory mediators. The current review focuses on conventional therapies, as well as crucial signaling pathways and promising therapeutic targets for post-SCI pain to provide new insights into the clinical treatment of post-SCI pain. The need to develop innovative delivery systems to treat SCI is also considered.

Acute post-injury blockade of α2δ-1 calcium channel subunits prevents pathological autonomic plasticity after spinal cord injury

After spinal cord injury (SCI), normally innocuous visceral or somatic stimuli can trigger uncontrolled reflex activation of sympathetic circuitry, causing pathological dysautonomia. We show that remarkable structural remodeling and plasticity occur within spinal autonomic circuitry, creating abnormal sympathetic reflexes that promote dysautonomia. However, when mice are treated early after SCI with human-equivalent doses of the US Food and Drug Administration (FDA)-approved drug gabapentin (GBP), it is possible to block multi-segmental excitatory synaptogenesis and abolish sprouting of autonomic neurons that innervate immune organs and sensory afferents that trigger pain and autonomic dysreflexia (AD). This “prophylactic GBP” regimen decreases the frequency and severity of AD and protects against SCI-induced immune suppression. These benefits persist even 1 month after stopping treatment. GBP could be repurposed to prevent dysautonomia in at-risk individuals with high-level SCI.

Brennan et al. show that α2δ−1 calcium channel subunits drive remarkable structural reorganization of autonomic circuitry and autonomic dysfunction after spinal cord injury. Early (prophylactic) post-injury treatment with gabapentin, an FDA-approved drug, prevents α2δ−1-dependent structural changes and autonomic dysfunction. Prophylactic gabapentin could be repurposed clinically for at-risk individuals.

Preliminary study of analgesic effect of bumetanide on neuropathic pain in patients with spinal cord injury

BACKGROUND/OBJECTIVE

The current study evaluated the analgesic effects of bumetanide as an adjunctive treatment in managing neuropathic pain following spinal cord injury. The peripheral expression level of Na-K-Cl-cotransporter-1 (NKCC1) and K-Cl-cotransporter-2 (KCC2) genes in polymorphonuclear lymphocytes (PMLs) assessed as a possible biomarker indicating central underlying mechanisms.

METHODS

This open-label, single-arm, pilot trial of bumetanide (2 mg/day) is an add-on treatment conducted in 14 SCI patients for 19 weeks. The whole duration consisted of three phases: pre-treatment (1 month), titration (3 weeks), and active treatment (4 months). Ultimately, nine patients completed the study. The primary outcome variables were the endpoint pain score measured by the numeric rating scale (NRS), and the short-form McGill Pain Questionnaire. Secondary endpoints included the Short-Form Health Survey that measures the quality of life. Blood samples were collected and used for determining the expression of NKCC1 and KCC2 genes in transcription and translation levels.

RESULTS

Bumetanide treatment significantly reduced average pain intensity according to the NRS and the short form of the McGill Pain Questionnaire scores. The baseline expression of KCC2 protein was low between groups and increased significantly following treatment (P < 0.05). Through the current study, pain improvement accompanied by the more significant mean change from the baseline for the overall quality of life.

CONCLUSION

These data might be a piece of preliminary evidence for the analgesic effect of bumetanide on neuropathic pain and could support the potential role of the upregulation of KCC2 protein and involvement of GABAergic disinhibition in producing neuropathic pain.

Management Strategies for Spinal Cord Injury Pain Updated for the Twenty-First Century

Traumatic spinal cord injury (SCI) often results in several life-altering impairments, including paralysis, sensory loss, and neurogenic bowel/bladder dysfunction. Some of these SCI-related conditions can be accommodated with compensatory strategies. Perhaps no SCI-associated condition is more troublesome and recalcitrant to the treating physiatrist than chronic neuropathic pain. In addition to the expected challenges in treating any chronic pain condition, treatment of SCI-related pain has the added difficulty of disruption of normal neural pathways that subserve pain transmission and attenuation. This article reviews selected treatment strategies for SCI-associated neuropathic pain.

Pregabalin and gabapentin in neuropathic pain management after spinal cord injury: a systematic review and meta-analysis

Neuropathic pain after spinal cord injury (SCI) has a significant negative impact on the patients’ quality of life. The objective of this systematic review is to examine the safety and efficacy of pregabalin (PGB) and gabapentin (GBP) in the treatment of neuropathic pain due to SCI. PubMed, the Cochrane Library, Embase, Scopus, and the Web of Science were searched up to December 2018. The reference lists of key and review studies were reviewed for additional citations. The quality of the studies was evaluated using the Cochrane Collaboration’s tools for assessing the risk of bias. A meta-analysis was performed for primary and secondary outcomes. Eight studies were eligible for inclusion. Meta-analysis of PGB vs. placebo showed that PGB was effective for neuropathic pain (standardized mean difference [SMD] = −0.40; 95% confidence interval [CI]: −0.78, −0.01), anxiety (MD = −0.68; 95% CI: −0.77, −0.59), depression (mean difference [MD] = −0.99; 95% CI: −1.08, −0.89), and sleep interference (MD = −1.08; 95% CI: −1.13, −1.02). Also, GBP was more effective than a placebo for reducing pain. No significant difference was observed between the efficacy of the two drugs (MD = −0.37; 95% CI: −1.67, 0.93). There was no significant difference between the two drugs for discontinuation due to adverse events (risk ratio = 3.00; 95% CI: 0.81, 11.15). PGB and GBP were effective vs. placebos in decreasing neuropathic pain after SCI. Also, there was no significant difference between the two drugs for decreasing pain and adverse events.

The analgesic effect of intravenous methylprednisolone on acute neuropathic pain with allodynia due to central cord syndrome: a retrospective study

Background

Central cord syndrome (CCS) may be associated with severe neuropathic pain that often resists to conventional pain therapy regimens and affects the patients’ quality of life (QoL) seriously. Current treatments for CCS-associated neuropathic pain have limited evidence of efficacy. This retrospective study was performed to present the effects of early treatment with methylprednisolone (MP) on acute neuropathic pain relief and the QoL in CCS patients.

Patients and methods

Data were collected from the medical records of CCS patients who suffered from acute neuropathic pain with allodynia. All the patients received intravenous MP treatment for up to 1 week. Patients were evaluated with standard measures of efficacy: neuropathic pain intensity, the area of allodynia, and the QoL at baseline, daily treatment, and at 1 and 3 months after the end of MP treatment.

Results

Thirty-four eligible patients were enrolled in our study. By the end of MP treatment, the proportion of patients who gained total or major (visual analog scale [VAS] score decreased by 50% or more) allodynia relief from the treatment was 91.18%, and a decrease in spontaneous pain was also observed. Moreover, this study showed MP could significantly improve the QoL of patients based on McGill Pain Questionnaire Short Form and EuroQol Five Dimensions Questionnaire. Four patients (11.76%) during MP treatment experienced mild or moderate side effects. None of the patients manifested CCS-associated neuropathic pain recurrence and MP-associated side effects at follow-up.

Conclusion

The current results suggested that MP offered an effective therapeutic alternative for relieving CCS-associated acute neuropathic pain with allodynia. Given the encouraging results of this study, it would be worthwhile to confirm these results in randomized placebo-controlled clinical trials.

Adverse cognitive effect of gabapentin in individuals with spinal cord injury: preliminary findings

Study design

Prospective observational cohort study.

Objectives

To assess the effects of gabapentin on neuropsychological variables including memory, attention, and executive function in individuals with spinal cord injury.

Setting

Santa Clara Valley Medical Center inpatient spinal cord injury unit.

Methods

Ten patients (three females, seven males) with traumatic spinal cord injury underwent testing, with a mean age of 35.6 years (range 19-59, SD ±15.74). There were five patients with tetraplegia and five with paraplegia. Nine tests to assess neuropsychological function and two tests to assess pain were performed at 1 week post initiation of therapy, and at 4 weeks post initiation of therapy. The neuropsychological tests assessed aspects of memory, attention, and executive function.

Results

The average score for six out of the nine neuropsychological items administered at 1 week post initiation of gabapentin displayed a decrease in cognitive function when compared to baseline. The average score for five out of nine neuropsychological items improved from 1 week post initiation of treatment to 4 weeks post initiation of treatment.

Conclusions

Gabapentin therapy is associated with a tangible decline in memory, executive function, and attention in individuals with spinal cord injury. However, owing to small sample size, loss of patient follow-up at the 4 week post-treatment assessment, and lack of a control group, we cannot definitively state that any decreases in cognition are solely attributable to treatment with gabapentin.

Antiepileptic drugs for chronic non-cancer pain in children and adolescents

BACKGROUND

Pain is a common feature of childhood and adolescence around the world, and for many young people, that pain is chronic. The World Health Organization (WHO) guidelines for pharmacological treatments for children's persisting pain acknowledge that pain in children is a major public health concern of high significance in most parts of the world. While in the past, pain was largely dismissed and was frequently left untreated, views on children's pain have changed over time, and relief of pain is now seen as importantWe designed a suite of seven reviews on chronic non-cancer pain and cancer pain (looking at antidepressants, antiepileptic drugs, non-steroidal anti-inflammatory drugs, opioids, and paracetamol) in order to review the evidence for children's pain utilising pharmacological interventions in children and adolescents.As the leading cause of morbidity in the world today, chronic disease (and its associated pain) is a major health concern. Chronic pain (that is pain lasting three months or longer) can occur in the paediatric population in a variety of pathophysiological classifications (nociceptive, neuropathic, or idiopathic) relating to genetic conditions, nerve damage pain, chronic musculoskeletal pain, and chronic abdominal pain, and for other unknown reasons.Antiepileptic (anticonvulsant) drugs, which were originally developed to treat convulsions in people with epilepsy, have in recent years been used to provide pain relief in adults for many chronic painful conditions and are now recommended for the treatment of chronic pain in the WHO list of essential medicines. Known side effects of antiepileptic drugs range from sweating, headache, elevated temperature, nausea, and abdominal pain to more serious effects including mental or motor function impairment.

OBJECTIVES

To assess the analgesic efficacy and adverse events of antiepileptic drugs used to treat chronic non-cancer pain in children and adolescents aged between birth and 17 years, in any setting.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) via the Cochrane Register of Studies Online, MEDLINE via Ovid, and Embase via Ovid from inception to 6 September 2016. We also searched the reference lists of retrieved studies and reviews as well as online clinical trial registries.

SELECTION CRITERIA

Randomised controlled trials, with or without blinding, by any route, treating chronic non-cancer pain in children and adolescents, comparing any antiepileptic drug with placebo or an active comparator.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed studies for eligibility. We planned to use dichotomous data to calculate risk ratio and number needed to treat for one additional event, using standard methods if data were available. We assessed the evidence using GRADE and created two 'Summary of findings' tables.

MAIN RESULTS

We included two studies with a total of 141 participants (aged 7 to 18 years) with chronic neuropathic pain, complex regional pain syndrome type 1 (CRPS-I), or fibromyalgia. One study investigated pregabalin versus placebo in participants with fibromyalgia (107 participants), and the other study investigated gabapentin versus amitriptyline in participants with CRPS-I or neuropathic pain (34 participants). We were unable to perform any quantitative analysis.Risk of bias for the two included studies varied, due to issues with randomisation (low to unclear risk), blinding of outcome assessors (low to unclear risk), reporting bias (low to unclear risk), the size of the study populations (high risk), and industry funding in the 'other' domain (low to unclear risk). We judged the remaining domains of sequence generation, blinding of participants and personnel, and attrition as low risk of bias. Primary outcomesOne study (gabapentin 900 mg/day versus amitriptyline 10 mg/day, 34 participants, for 6 weeks) did not report our primary outcomes (very low-quality evidence).The second study (pregabalin 75 to 450 mg/day versus placebo 75 to 450 mg/day, 107 participants, for 15 weeks) reported no significant change in pain scores for pain relief of 30% or greater between pregabalin 18/54 (33.3%), and placebo 16/51 (31.4%), P = 0.83 (very low-quality evidence). This study also reported Patient Global Impression of Change, with the percentage of participants feeling "much or very much improved" with pregabalin 53.1%, and placebo 29.5% (very low-quality evidence).We downgraded the evidence by three levels to very low for one of two reasons: due to the fact that there was no evidence to support or refute the use of the intervention, or that there were too few data and the number of events was too small to be meaningful. Secondary outcomesIn one small study, adverse events were uncommon: gabapentin 2 participants (2 adverse events); amitriptyline 1 participant (1 adverse event) (6-week trial). The second study reported a higher number of adverse events: pregabalin 38 participants (167 adverse events); placebo 34 participants (132 adverse events) (15-week trial) (very low-quality evidence).Withdrawals due to adverse events were infrequent in both studies: pregabalin (4 participants), placebo (4 participants), gabapentin (2 participants), and amitriptyline (1 participant) (very low-quality evidence).Serious adverse events were reported in both studies. One study reported only one serious adverse event (cholelithiasis and major depression resulting in hospitalisation in the pregabalin group) and the other study reported no serious adverse events (very low-quality evidence).There were few or no data for our remaining secondary outcomes (very low-quality evidence).We downgraded the evidence by three levels to very low due to too few data and the fact that the number of events was too small to be meaningful.

AUTHORS' CONCLUSIONS

This review identified only two small studies, with insufficient data for analysis.As we could undertake no meta-analysis, we were unable to comment about efficacy or harm from the use of antiepileptic drugs to treat chronic non-cancer pain in children and adolescents. Similarly, we could not comment on our remaining secondary outcomes: Carer Global Impression of Change; requirement for rescue analgesia; sleep duration and quality; acceptability of treatment; physical functioning; and quality of life.We know from adult randomised controlled trials that some antiepileptics, such as gabapentin and pregabalin, can be effective in certain chronic pain conditions.We found no evidence to support or refute the use of antiepileptic drugs to treat chronic non-cancer pain in children and adolescents.

Neuropathic Pain and Spinal Cord Injury: Phenotypes and Pharmacological Management

Chronic neuropathic pain is a complicated condition after a spinal cord injury (SCI) that often has a lifelong and significant negative impact on life after the injury; therefore, improved pain management is considered a significant and unmet need. Neuropathic pain mechanisms are heterogeneous and the difficulty in determining their individual contribution to specific pain types may contribute to poor treatment outcomes in this population. Thus, identifying human neuropathic pain phenotypes based on pain symptoms, somatosensory changes, or cognitive and psychosocial factors that reflect specific spinal cord or brain mechanisms of neuropathic pain is an important goal. Once a pain phenotype can be reliably replicated, its relationship with biomarkers and clinical treatment outcomes can be analyzed, and thereby facilitate translational research and further the mechanistic understanding of individual differences in the pain experience and in clinical trial outcomes. The present article will discuss clinical aspects of SCI-related neuropathic pain, neuropathic pain phenotypes, pain mechanisms, potential biomarkers and pharmacological interventions, and progress regarding how defining neuropathic pain phenotypes may lead to more targeted treatments for these difficult pain conditions.

Central Mechanisms Mediating Thrombospondin-4-induced Pain States

Peripheral nerve injury induces increased expression of thrombospondin-4 (TSP4) in spinal cord and dorsal root ganglia that contributes to neuropathic pain states through unknown mechanisms. Here, we test the hypothesis that TSP4 activates its receptor, the voltage-gated calcium channel Cavα2δ1 subunit (Cavα2δ1), on sensory afferent terminals in dorsal spinal cord to promote excitatory synaptogenesis and central sensitization that contribute to neuropathic pain states. We show that there is a direct molecular interaction between TSP4 and Cavα2δ1 in the spinal cord in vivo and that TSP4/Cavα2δ1-dependent processes lead to increased behavioral sensitivities to stimuli. In dorsal spinal cord, TSP4/Cavα2δ1-dependent processes lead to increased frequency of miniature and amplitude of evoked excitatory post-synaptic currents in second-order neurons as well as increased VGlut2- and PSD95-positive puncta, indicative of increased excitatory synapses. Blockade of TSP4/Cavα2δ1-dependent processes with Cavα2δ1 ligand gabapentin or genetic Cavα2δ1 knockdown blocks TSP4 induced nociception and its pathological correlates. Conversely, TSP4 antibodies or genetic ablation blocks nociception and changes in synaptic transmission in mice overexpressing Cavα2δ1 Importantly, TSP4/Cavα2δ1-dependent processes also lead to similar behavioral and pathological changes in a neuropathic pain model of peripheral nerve injury. Thus, a TSP4/Cavα2δ1-dependent pathway activated by TSP4 or peripheral nerve injury promotes exaggerated presynaptic excitatory input and evoked sensory neuron hyperexcitability and excitatory synaptogenesis, which together lead to central sensitization and pain state development.

Gabapentinoid Insensitivity after Repeated Administration is Associated with Down-Regulation of the α(2)δ-1 Subunit in Rats with Central Post-Stroke Pain Hypersensitivity

The α2δ-1 subunit of the voltage-gated Ca(2+) channel (VGCC) is a molecular target of gabapentin (GBP), which has been used as a first-line drug for the relief of neuropathic pain. GBP exerts its anti-nociceptive effects by disrupting trafficking of the α2δ-1 subunit to the presynaptic membrane, resulting in decreased neurotransmitter release. We previously showed that GBP has an anti-allodynic effect in the first two weeks; but this is followed by insensitivity in the later stage after repeated administration in a rat model of central post-stroke pain (CPSP) hypersensitivity induced by intra-thalamic hemorrhage. To explore the mechanisms underlying GBP insensitivity, the cellular localization and time-course of expression of the α2δ-1 subunit in both the thalamus and spinal dorsal horn were studied in the same model. We found that the α2δ-1 subunit was mostly localized in neurons, but not astrocytes and microglia. The level of α2δ-1 protein increased in the first two weeks after injury but then decreased in the third week, when GBP insensitivity occurred. Furthermore, the α2δ-1 down-regulation was likely caused by later neuronal loss in the injured thalamus through a mechanism other than apoptosis. In summary, the present results suggest that the GBP receptor α2δ-1 is mainly expressed in thalamic neurons in which it is up-regulated in the early stage of CPSP but this is followed by dramatic down-regulation, which is likely associated with GBP insensitivity after long-term use.

Gabapentin Effects on PKC-ERK1/2 Signaling in the Spinal Cord of Rats with Formalin-Induced Visceral Inflammatory Pain

Currently, the clinical management of visceral pain remains unsatisfactory for many patients suffering from this disease. While preliminary animal studies have suggested the effectiveness of gabapentin in successfully treating visceral pain, the mechanism underlying its analgesic effect remains unclear. Evidence from other studies has demonstrated the involvement of protein kinase C (PKC) and extracellular signal-regulated kinase1/2 (ERK1/2) in the pathogenesis of visceral inflammatory pain. In this study, we tested the hypothesis that gabapentin produces analgesia for visceral inflammatory pain through its inhibitory effect on the PKC-ERK1/2 signaling pathway. Intracolonic injections of formalin were performed in rats to produce colitis pain. Our results showed that visceral pain behaviors in these rats decreased after intraperitoneal injection of gabapentin. These behaviors were also reduced by intrathecal injections of the PKC inhibitor, H-7, and the ERK1/2 inhibitor, PD98059. Neuronal firing of wide dynamic range neurons in L6–S1 of the rat spinal cord dorsal horn were significantly increased after intracolonic injection of formalin. This increased firing rate was inhibited by intraperitoneal injection of gabapentin and both the individual and combined intrathecal application of H-7 and PD98059. Western blot analysis also revealed that PKC membrane translocation and ERK1/2 phosphorylation increased significantly following formalin injection, confirming the recruitment of PKC and ERK1/2 during visceral inflammatory pain. These effects were also significantly reduced by intraperitoneal injection of gabapentin. Therefore, we concluded that the analgesic effect of gabapentin on visceral inflammatory pain is mediated through suppression of PKC and ERK1/2 signaling pathways. Furthermore, we found that the PKC inhibitor, H-7, significantly diminished ERK1/2 phosphorylation levels, implicating the involvement of PKC and ERK1/2 in the same signaling pathway. Thus, our results suggest a novel mechanism of gabapentin-mediated analgesia for visceral inflammatory pain through a PKC-ERK1/2 signaling pathway that may be a future therapeutic target for the treatment of visceral inflammatory pain.

Management of Neuropathic Pain Associated with Spinal Cord Injury

Spinal cord injury (SCI) is an injury to the spinal cord that leads to varying degrees of motor and/or sensory deficits and paralysis. Chronic pain of both neuropathic and nociceptive type is common and contributes to reduced quality of life. The aim of the review is to provide current clinical understanding as well as discuss and evaluate efficacy of pharmacological interventions demonstrated in the clinical studies. The review was based on literature search in PubMed and Medline with words "neuropathic pain" and "spinal cord injury". The review included clinical studies and not experimental data nor case reports. A limited number of randomized and placebo-controlled studies concerning treatment options of neuropathic pain after SCI were identified. Amitriptyline, a tricyclic antidepressant and the antiepileptic drugs, gabapentin and pregabalin, are most studied with demonstrated efficacy, and considered to be the primary choice. Opioids have demonstrated conflicting results in the clinical studies. In addition, administration route used in the studies as well as reported side effects restrict everyday use of opioids as well as ketamine and lidocaine. Topical applications of capsaicin or lidocaine as well as intradermal injections of Botulinum toxin are new treatment modalities that are so far not studied on SCI population and need further studies. Non-pharmacological approaches may have additional effect on neuropathic pain. Management of pain should always be preceded by thorough clinical assessment of the type of pain. Patients need a follow-up to evaluate individual effect of applied measures. However, the applied management does not necessarily achieve satisfactory pain reduction. Further clinical studies are needed to evaluate the effect of both established and novel management options.

Post-stroke pain hypersensitivity induced by experimental thalamic hemorrhage in rats is region-specific and demonstrates limited efficacy of gabapentin

Intractable central post-stroke pain (CPSP) is one of the most common sequelae of stroke, but has been inadequately studied to date. In this study, we first determined the relationship between the lesion site and changes in mechanical or thermal pain sensitivity in a rat CPSP model with experimental thalamic hemorrhage produced by unilateral intra-thalamic collagenase IV (ITC) injection. Then, we evaluated the efficacy of gabapentin (GBP), an anticonvulsant that binds the voltage-gated Ca(2+) channel α2δ and a commonly used anti-neuropathic pain medication. Histological case-by-case analysis showed that only lesions confined to the medial lemniscus and the ventroposterior lateral/medial nuclei of the thalamus and/or the posterior thalamic nucleus resulted in bilateral mechanical pain hypersensitivity. All of the animals displaying CPSP also had impaired motor coordination, while control rats with intra-thalamic saline developed no central pain or motor deficits. GBP had a dose-related anti-allodynic effect after a single administration (1, 10, or 100 mg/kg) on day 7 post-ITC, with significant effects lasting at least 5 h for the higher doses. However, repeated treatment, once a day for two weeks, resulted in complete loss of effectiveness (drug tolerance) at 10 mg/kg, while effectiveness remained at 100 mg/kg, although the time period of efficacious analgesia was reduced. In addition, GBP did not change the basal pain sensitivity and the motor impairment caused by the ITC lesion, suggesting selective action of GBP on the somatosensory system.

Effect of intermittent normobaric hyperoxia for treatment of neuropathic pain in Chinese patients with spinal cord injury

STUDY DESIGN

Prospective, randomized and controlled study.

OBJECTIVES

The aim of the study was to investigate the effect of intermittent normobaric hyperoxia (InHO) for treatment of neuropathic pain in patients with spinal cord injury (SCI).

SETTING

The First Affiliated Hospital of Nanhua University, Hengyang, Hunan Province, China.

METHODS

Patients with SCI from Hunan Province were recruited from the First Affiliated Hospital of Nanhua University. History, duration, localization and characteristics of pain were recorded. Visual analog scale (VAS), the Patient Global Impression of Change (PGIC) and Short Form-36 walk-wheel (SF-36ww) was used to investigate the effect of InHO. Patients were randomly assigned to study and control groups. In study group, patients were exposed to pure oxygen via non-rebreathing reservoir mask, which increased the provided oxygen at a rate of 7 l min^-1 for 1 or 4 h daily in 2 weeks. While in control group, patients breathed air via non-rebreathing reservoir mask at the same rate.

RESULTS

A total of 62 SCI patients with neuropathic pain were included in the study. The mean age of the patients was 36.85±10.71 years. Out of 62 patients, 21 were tetraplegic and 41 were paraplegic. Overall, 14 patients had complete SCI while 48 patients had incomplete injuries. Three groups were similar with respect to age, gender, duration, smoker or not, level and severity of injury. In the 4 h per day InHO groups, a statistically significant reduction of the VAS values was observed (P<0.05). Significant difference was also found in SF-36ww pain scores and PGIC (P<0.05). However, such an effect was not evident in the control group.

CONCLUSION

This study revealed that in treatment of neuropathic pain of SCI patients, InHO may be effective.

PERSPECTIVE

This article presents InHO may effectively complement pharmacological treatment in patients with SCI and neuropathic pain.

Gabapentinoids are effective in decreasing neuropathic pain and other secondary outcomes after spinal cord injury: a meta-analysis

OBJECTIVE

To examine the effectiveness of gabapentin and pregabalin in diminishing neuropathic pain and other secondary conditions in individuals with spinal cord injury (SCI).

DATA SOURCES

A systematic search was conducted using multiple databases for relevant articles published from 1980 to June 2013.

STUDY SELECTION

Controlled and uncontrolled trials involving gabapentin and pregabalin for treatment of neuropathic pain, with ≥3 subjects and ≥50% of study population with SCI, were included.

DATA EXTRACTION

Two independent reviewers selected studies based on inclusion criteria and then extracted data. Pooled analysis using Cohen's d to calculate standardized mean difference (SMD), SE, and 95% confidence interval (CI) for primary (pain) and secondary outcomes (anxiety, depression, sleep interference) was conducted.

DATA SYNTHESIS

Eight studies met inclusion criteria. There was a significant reduction in the intensity of neuropathic pain at <3 months (SMD=.96±.11; 95% CI, .74-1.19; P<.001) and between 3 and 6 months (SMD=2.80±.18; 95% CI, 2.44-3.16; P<.001). A subanalysis found a significant decrease in pain with gabapentin (SMD=1.20±.16; 95% CI, .88-1.52; P<.001) and with pregabalin (SMD=1.71±.13; 95% CI, 1.458-1.965; P<.001). A significant reduction in other SCI secondary conditions, including sleep interference (SMD=1.46±.12; 95% CI, 1.22-1.71; P<.001), anxiety (SMD=1.05±.12; 95% CI, .81-1.29; P<.001), and depression (SMD=1.22±.13; 95% CI, .967-1.481; P<.001) symptoms, was shown. A significantly higher risk of dizziness (risk ratio [RR]=2.02, P=.02), edema (RR=6.140, P=.04), and somnolence (RR=1.75, P=.01) was observed.

CONCLUSIONS

Gabapentin and pregabalin appear useful for treating pain and other secondary conditions after SCI. Effectiveness comparative to other analgesics has not been studied. Patients need to be monitored closely for side effects.

Anticonvulsant medication use for the management of pain following spinal cord injury: systematic review and effectiveness analysis

STUDY DESIGN

Systematic review and effectiveness analysis.

OBJECTIVES

Assess the effectiveness of anticonvulsants for the management of post spinal cord injury (SCI) neuropathic pain.

SETTING

Studies from multiple countries were included.

METHODS

CINAHL, Cochrane, EMBASE and MEDLINE were searched up to April 2013. Quality assessment was conducted using the Jadad and the Downs and Black tools. Effect sizes and odds ratios were calculated for primary and secondary outcome in the included studies.

RESULTS

Gabapentinoids, valproate, lamotrigine, levetiracetam and carbamazepine were examined in the 13 included studies, ten of which are randomized controlled trials. Large effect size (0.873-3.362) for improvement of pain relief was found in 4 of the 6 studies examining the effectiveness of gabapentin. Pregabalin was shown to have a moderate to large effect (0.695-3.805) on improving neuropathic pain post SCI in 3 studies. Valproate and levetiracetam were not effective in improving neuropathic pain post SCI, while lamotrigine was effective in reducing neuropathic pain amongst persons with incomplete lesions and carbamazepine was found effective for relief of moderate to intense pain.

CONCLUSION

Gabapentin and pregabalin are the two anticonvulsants which have been shown to have some benefit in reducing neuropathic pain.

Neuropathic pain in patients with spinal cord injury: report of 213 patients

Objective Management of neuropathic pain following spinal cord injury (SCI) can be a frustrating experience for patients since it poses a therapeutic challenge. In this article the authors describe the clinical characteristics of a group of patients with pain after spinal cord injury. Methods In this retrospective study, 213 patients with SCI and neuropathic pain were assessed. We analyzed clinical characteristics, treatment options, and pain intensity for these patients. Results The main cause of SCI was spine trauma, which occurred in 169 patients, followed by tumors and infection. Complete lesions were verified in 144 patients. In our study, patients with traumatic SCI and partial lesions seem to be presented with more intense pain; however, this was not statistically significant. Conclusions Neuropathic pain is a common complaint in patients with SCI and presents a treatment challenge. Knowledge of the clinical characteristics of this group of patients may help determine the best approach to intervention.

Inhibition of ROS-induced p38MAPK and ERK activation in microglia by acupuncture relieves neuropathic pain after spinal cord injury in rats

Acupuncture (AP) is currently used worldwide to relieve pain. However, little is known about its mechanisms of action. We found that after spinal cord injury (SCI), AP inhibited the production of superoxide anion (O(2)·), which acted as a modulator for microglial activation, and the analgesic effect of AP was attributed to its anti-microglial activating action. Direct injection of a ROS scavenger inhibited SCI-induced NP. After contusion injury which induces the below-level neuropathic pain (NP), Shuigou and Yanglingquan acupoints were applied. AP relieved mechanical allodynia and thermal hyperalgesia, while vehicle and simulated AP did not. AP also decreased the proportion of activated microglia, and inhibited both p38MAPK and ERK activation in microglia at the L4-5. Also, the level of prostaglandin E(2) (PGE2), which is produced via ERK signaling and mediates the below-level pain through PGE2 receptor, was reduced by AP. Injection of p38MAPK or ERK inhibitors attenuated NP and decreased PGE2 production. Furthermore, ROS produced after injury-induced p38MAPK and ERK activation in microglia, and mediated mechanical allodynia and thermal hyperalgesia, which were inhibited by AP or a ROS scavenger. AP also inhibited the expression of inflammatory mediators. Therefore, our results suggest that the analgesic effect of AP may be partly mediated by inhibiting ROS-induced microglial activation and inflammatory responses after SCI and provide the possibility that AP can be used effectively as a non-pharmacological intervention for SCI-induced chronic NP in patients.

The clinical characteristics of neuropathic pain in patients with spinal cord injury

OBJECTIVES

The aim of the study was to evaluate the characteristics of neuropathic pain and observe intensity alterations in pain with regard to time during the day in spinal cord injury (SCI) patients.

METHODS

A total of 50 SCI patients (M/F, 40/10; mean age, 35±12 years) with at-level and below-level neuropathic pain were included in the study. All patients were examined and classified according to the ASIA/ISCoS 2002 International Neurologic Examination and Classification Standards. The history, duration, localization and characteristics of the pain were recorded. Neuropathic pain of patients was evaluated with the McGill-Melzack Pain Questionnaire and LANSS (Leeds Assessment of Neuropathic Symptoms and Signs) Pain Scale. Visual analog scale (VAS) was used to measure the severity of pain four times during the day. Quality of life was analyzed with Short Form 36.

RESULTS

Out of 50 patients, 10 were tetraplegic and 40 were paraplegic. In all, 28 patients had motor and sensory complete injuries (AIS A), whereas 22 patients had sensory incomplete (AIS B, C and D) injuries. The most frequently used words to describe neuropathic pain were throbbing, tiring, hot and tingling. Pain intensity was significantly higher in the night than in the evening, noon and morning (P<0.05) (VAS morning: 5.16±2.42, VAS noon: 5.24±2.52, VAS evening: 5.80±2.46 and VAS night: 6.38±2.19).

CONCLUSION

Neuropathic pain is a serious complaint in SCI patients and affects their quality of life. Neuropathic pain intensity was higher in the night hours than other times of day. This situation reinforces the need for a continued research and education on neuropathic pain in SCI.

Simultaneous quantification of levetiracetam and gabapentin in plasma by ultra-pressure liquid chromatography coupled with tandem mass spectrometry detection

INTRODUCTION

Gabapentin (Neurontin) and levetiracetam (Keppra) are anticonvulsants with novel structures and suggested therapeutic ranges of 2-10 mg/L and 6-20 mg/L, respectively. Gabapentin is also used extensively to manage neuropathic pain, and for this indication, wherein higher doses are prescribed, plasma concentrations of 15-30 mg/L are typical.

OBJECTIVE

Here, we describe a simple rapid assay to support therapeutic drug monitoring of gabapentin and levetiracetam in plasma by ultra-pressure liquid chromatography couples to tandem mass spectrometry (UPLC-MS/MS) detection.

METHODS

After the addition of internal standard and protein precipitation of patient plasma with methanol:acetonitrile in a 50:50 ratio, 1 μL of supernatant sample is injected onto an Acquity UPLC HSS T3, 1.8 μm, 2.1 × 50 mm (Waters) column. Elution occurs using a linear gradient of acetonitrile and water, each having 0.1% formic acid added. The column is eluted into a Waters Acquity UPLC TQD, operating in a positive mode to detect gabapentin at transition 172.18 > 154.11, levetiracetam at 171.11 > 126, and internal standard (3-amino-2-naphthoic acid) at 188.06 > 170. Secondary transitions for each analyte are also monitored for gabapentin at 172.18 > 137.06, levetiracetam at 171.11 > 154, and internal standard at 188.06 > 115. Runtime is 1.5 minutes per injection with baseline resolved chromatographic separation.

RESULTS

The analytical measurement ranges were 1-150 mg/L for gabapentin and for levetiracetam. Intra-assay imprecision by the coefficient of variance (CV) was less than 8% and interassay CV was less than 5% for both analytes, at 4 different concentrations. Results obtained from patient samples were compared with results generated by established high-performance liquid chromatography-UV methods with the following regression statistics: y = 1.12x - 0.77, r = 0.996, Sy, x = 0.89, and n = 29 for gabapentin and y = 0.991x + 0.70, r = 0.997, Sy, x = 2.24, and n = 30 for levetiracetam. No analytical interferences were identified.

CONCLUSION

: In summary, a simple reliable UPLC-MS/MS method was developed and validated for routine clinical monitoring of gabapentin and levetiracetam.

Use of a gonadotrophin-releasing hormone vaccine in headshaking horses

The aim of this study was to investigate the use of a gonadotrophin-releasing hormone (GnRH) vaccine in the treatment of headshaking in horses. Fifteen geldings received two doses of the GnRH vaccine four weeks apart. Serum was collected before and after vaccination to measure concentrations of luteinising hormone (LH) (10 horses) and follicle-stimulating hormone (FSH) (six horses). Owners recorded the frequency of seven common headshaking behaviours using a visual analogue scale (VAS) before vaccination and at two, four, eight, 12, 16 and 20 weeks after vaccination. Serum LH (P=0.008) and FSH (P=0.03) concentrations decreased significantly following vaccination. Although approximately one-third of the owners reported a subjective improvement in headshaking, serial scoring did not indicate a reduction in headshaking behaviours following vaccination with a commercial GnRH vaccine. Vaccination reactions were observed in four of 15 horses (27 per cent), including one case of severe, presumed immune-mediated, myositis.

A systematic review of pharmacologic treatments of pain after spinal cord injury

OBJECTIVE

To conduct a systematic review of published research on the pharmacologic treatment of pain after spinal cord injury (SCI).

DATA SOURCES

MEDLINE, CINAHL, EMBASE, and PsycINFO databases were searched for articles published 1980 to June 2009 addressing the treatment of pain post SCI. Randomized controlled trials (RCTs) were assessed for methodologic quality using the Physiotherapy Evidence Database (PEDro) assessment scale, whereas non-RCTs were assessed by using the Downs and Black (D&B) evaluation tool. A level of evidence was assigned to each intervention by using a modified Sackett scale.

STUDY SELECTION

The review included RCTs and non-RCTs, which included prospective controlled trials, cohort, case series, case-control, pre-post studies, and post studies. Case studies were included only when there were no other studies found.

DATA EXTRACTION

Data extracted included the PEDro or D&B score, the type of study, a brief summary of intervention outcomes, the type of pain, the type of pain scale, and the study findings.

DATA SYNTHESIS

Articles selected for this particular review evaluated different interventions in the pharmacologic management of pain after SCI. Twenty-eight studies met inclusion criteria; there were 21 randomized controlled trials; of these, 19 had level 1 evidence. Treatments were divided into 5 categories: anticonvulsants, antidepressants, analgesics, cannabinoids, and antispasticity medications.

CONCLUSIONS

Most studies did not specify participants' types of pain, making it difficult to identify the type of pain being targeted by the treatment. Anticonvulsant and analgesic drugs had the highest levels of evidence and were the drugs most often studied. Gabapentin and pregabalin had strong evidence (5 level 1 RCTs) for effectiveness in treating post-SCI neuropathic pain as did intravenous analgesics (lidocaine, ketamine, and morphine), but the latter only had short-term benefits. Tricyclic antidepressants only showed benefit for neuropathic pain in depressed persons. Intrathecal baclofen reduced musculoskeletal pain associated with spasticity; however, there was conflicting evidence for the reduction in neuropathic pain. Studies assessing the effectiveness of opioids were limited and revealed only small benefits. Cannabinoids showed conflicting evidence in improving spasticity-related pain. Clonidine and morphine when given together had a significant synergistic neuropathic pain-relieving effect.

Gabapentin and pregabalin ameliorate mechanical hypersensitivity after spinal cord injury in mice

The antiepileptic drugs gabapentin and pregabalin exhibit well-established analgesic effects in patients with several neuropathic conditions. In the present study, we examined their effects on mechanical hypersensitivity in mice subjected to weight-drop spinal cord injury. Hindlimb motor function and mechanical hypersensitivity were evaluated using the Basso-Beattie-Bresnahan (BBB) locomotor rating scale and the von Frey test, respectively, for 4 weeks after spinal cord injury. Despite gradual recovery of hindlimb motor function after spinal cord injury, mice exhibited continuous development of mechanical hypersensitivity. Gabapentin (30 and 100 mg/kg) and pregabalin (10 and 30 mg/kg), administered intraperitoneally on the 28th day after spinal cord injury, reduced mechanical hypersensitivity in a dose-dependent manner. These results suggest that gabapentin and pregabalin could be useful therapeutic tools for patients with neuropathic pain after spinal cord injury.

Efficacy of pregabalin and gabapentin for neuropathic pain in spinal-cord injury: an evidence-based evaluation of the literature

BACKGROUND

Spinal-cord injury (SCI) is a leading cause of neuropathic pain (NP). Current pharmaceutical treatments for NP in SCI patients are not effective. Two promising options are gabapentin (GP) and pregabalin (PB). Their predominant mechanism of action is believed to be the inhibition of calcium currents, leading in turn to reduced neurotransmitter release and attenuation of postsynaptic excitability. This could explain much of their efficacy in the treatment of both seizure disorders and pain syndromes. However, evidence for their efficacy in attenuating NP of SCI is still controversial.

OBJECTIVE

To efficiently integrate valid information and provide a basis for rational decision making, through determining PB and GP efficacy in treating NP in SCI.

METHODS

Literature was systematically reviewed. Medline, Embase, CINAHL and Cochrane Database were searched using search terms 'gabapentin', 'pregabalin', 'neurontin', 'lyrica', 'neuropathic pain' and 'spinal-cord injury'. Studies were assessed independently by two authors.

RESULTS

Five studies were eligible for inclusion. Two of them studied PB and three GP. Both GP and PB appear to be efficacious for NP in SCI. A clear comparison between the two drugs could not be performed. The literature data suggest that PB is more efficacious than GP in many important variables for NP in SCI, although PB use is followed by more side effects than GP. PB reduced Visual Analogue Score (VAS) in both studies (P < 0.001 and P = 0.016). On the other hand, for GP a maximum dosage of 3,600 mg/day reduced VAS score (P = 0.000), whereas a maximum dosage of 1,200 mg/day failed to do so.

CONCLUSION

There is a lack of studies comparing GP and PB in treating NP in SCI. This systematic review indicates the possible efficacy of PB and GP in NP of SCI. Recommendations for future research to inform clinical practice should include cost-effectiveness studies and dose-response analysis in order to determine the schema employed and the duration of treatment.

Pregabalin in the management of central neuropathic pain

Central neuropathic pain is a painful condition, often severe, that occurs in a person who is already affected by an injury or disease of the brain or spinal cord. This dual insult is especially threatening to the quality of life of a person and their ability to perform even the most basic of tasks. Despite this high level of suffering there are relatively few trials investigating the management of central neuropathic pain. However, two randomised placebo-controlled studies have recently emerged demonstrating efficacy of pregabalin in reducing central neuropathic pain due to spinal cord injury and central poststroke pain. Pregabalin, an anticonvulsant, has been shown to be efficacious in the management of peripheral neuropathic pain of various causes and now may have a role to play in central neuropathic pain.

Calcium Channels As Therapeutic Targets in Neuropathic Pain

Injury to the nerve can produce changes in dorsal horn function and pain. This facilitated processing may be mediated in part by voltage-sensitive calcium channels. Activation of these channels increases intracellular calcium, thereby mediating transmitter release and activating cascades serving to alter membrane excitability and initiate protein transcription. Molecular techniques reveal the complexity and multiplicity of these channels. At the spinal level, blocking of several of these calcium channels, notably those of the N type, can prominently alter pain behavior. These effects are consistent with the high levels of expression on primary afferents and dorsal horn neurons of these channels. More recently, agents binding to auxiliary subunits such as the alpha2delta of these calcium channels diminish excitability of the membrane without completely blocking channel function. Drugs that bind to this site, highly expressed in the superficial dorsal horn, will diminish neuropathic pain states. Continuing developments in our understanding of these channel functions promises to advance the control of aberrant spinal functions initiated by nerve injury.

PERSPECTIVE

Pharmacologic studies showing the role of spinal voltage-sensitive calcium channels in neuropathic pain models provide evidence suggesting their applicability in human pain states.