Pregabalin: a better neuropathic pain treatment in rodents than in humans

Pharmacotherapy and noninvasive neurostimulation for neuropathic pain

Neuropathic pain poses a significant challenge due to its complex mechanisms, necessitating specific treatments. In recent decades, significant progress has been made in the clinical research of neuropathic pain, marking a shift from empirical strategies to evidence-based medicine in its management. This review outlines both pharmacological and non-pharmacological interventions. Antidepressants (tricyclic and serotonin-noradrenaline reuptake inhibitors), antiepileptics (gabapentin, pregabalin), and topical agents constitute the main pharmacological treatments. These approaches target peripheral or central mechanisms associated with neuropathic pain. Noninvasive neurostimulation, including transcutaneous electrical nerve stimulation (TENS) and repetitive transcranial magnetic stimulation (rTMS), provides non-pharmacological alternatives. However, challenges persist in effectively targeting existing medications and developing drugs that act on novel targets, necessitating innovative therapeutic strategies.

Neuropathic pain: Evidence based recommendations

Neuropathic pain continues to be a significant problem that lacks effective solutions for every single patient. In 2015, international guidelines (NeuPSIG) were published, while the French recommendations were updated in 2020. The purpose of this minireview is to provide an update on the process of developing evidence-based recommendations and explore potential changes to the current recommendations. Primary treatments for neuropathic pain include selective serotonin-norepinephrine reuptake inhibitors (SNRIs) such as duloxetine and venlafaxine, gabapentin, tricyclic antidepressants, as well as topical lidocaine and transcutaneous electrical nerve stimulation, which are specifically suggested for focal peripheral neuropathic pain. Pregabalin is a first line treatment according to international guidelines but second-line in the more recent French guidelines, due to lower efficacy seen in more recent studies and misuse risk. Additionally, tramadol, combination therapies, and psychotherapy as adjuncts are proposed second line; high-concentration capsaicin patches, and botulinum toxin A are proposed specifically for focal peripheral neuropathic pain. In cases where primary and secondary treatments prove insufficient, third-line options come into play. These include high-frequency repetitive transcranial magnetic stimulation (rTMS) targeting the motor cortex, spinal cord stimulation, and the use of strong opioids when no alternative is available. To ensure optimal management of neuropathic pain in real-life situations, it is imperative to disseminate these recommendations widely and secure the acceptance of practitioners. By doing so, we can bridge the gap between theory and practice, and enhance the overall care and treatment of individuals suffering from neuropathic pain.

Transcranial Magnetic Stimulation to Treat Neuropathic Pain: A Bibliometric Analysis

Neuropathic pain is caused by a lesion or disease of the somatosensory system and is one of the most incapacitating pain types, representing a significant non-met medical need. Due to the increase in research in the field and since innovative therapeutic strategies are required, namely in intractable neuropathic pain, neurostimulation has been used. Within this approach, transcranial magnetic stimulation (TMS) that uses a transient magnetic field to produce electrical currents over the cortex emerges as a popular method in the literature. Since this is an area in expansion and due to the putative role of TMS, we performed a bibliometric analysis in Scopus with the primary objective of identifying the scientific production related to the use of TMS to manage neuropathic pain. The research had no restrictions, and the analysis focused on the characteristics of the literature retrieved, scientific collaboration and main research topics from inception to 6 July 2023. A total of 474 articles were collected. A biggest co-occurrence between the terms "neuropathic pain" and "transcranial magnetic stimulation" was obtained. The journal "Clinical Neurophysiology" leads the Top 5 most productive sources. The United States is the most productive country, with 50% of US documents being "review articles", followed by France, with 56% of French documents being "original articles". Lefaucheur, JP and Saitoh, Y are the two most influential authors. The most frequent type of document was "original article". Most of the studies (34%) that identified the neuropathic pain type focused on traumatic neuropathic pain, although a large proportion (38%) did not report the neuropathic pain type. This study allows us to provide a general overview of the field of TMS application for neuropathic pain and is useful for establishing future directions of research in this field.

Advances and challenges in neuropathic pain: a narrative review and future directions

Over the past few decades, substantial advances have been made in neuropathic pain clinical research. An updated definition and classification have been agreed. Validated questionnaires have improved the detection and assessment of acute and chronic neuropathic pain; and newer neuropathic pain syndromes associated with COVID-19 have been described. The management of neuropathic pain has moved from empirical to evidence-based medicine. However, appropriately targeting current medications and the successful clinical development of drugs acting on new targets remain challenging. Innovative approaches to improving therapeutic strategies are required. These mainly encompass rational combination therapy, drug repurposing, non-pharmacological approaches (such as neurostimulation techniques), and personalised therapeutic management. This narrative review reports historical and current perspectives regarding the definitions, classification, assessment, and management of neuropathic pain and explores potential avenues for future research.

Mirror peripheral neuropathy and unilateral chronic neuropathic pain: insights from asymmetric neurological patterns in leprosy

ABSTRACT

Leprosy-related multiple mononeuropathy offers a pattern of impairment where neuropathy with and without neuropathic pain (NeP) are present in the same individual, thus allowing to investigate peripheral sensory and innervation in both conditions. This cross-sectional study collected data on clinical and neurological examination, pain assessment questionnaires, quantitative sensory test, and intraepidermal nerve fiber density of patients with leprosy and divided the cohort into 2 groups: with NeP (P+) and without NeP (P-). Furthermore, we assessed mirror body areas in the same NeP individuals with bilateral neuropathy also presenting unilateral NeP. Pain-free patients having unilateral neuropathy were controls. A total of 37 P+ and 22 P- patients were evaluated. Limb areas with NeP had signs of C-fiber dysfunction and hyperesthesia on quantitative sensory testing compared with limb areas having neuropathy without NeP. Skin denervation was found in all patients with leprosy. Comparisons of limbs with and without neuropathy and with and without NeP revealed that higher heat pain thresholds (HPTs) were associated with neuropathic pain areas, whereas less altered HPT was correlated with higher fiber density. Furthermore, a relationship was found between time of leprosy treatment termination and more intense neuropathy, expressed by HPT increasing 0.03°C each month. As expected, interindividual comparisons failed to show differences in intraepidermal nerve fiber density and subepidermal plexus areas between P+ and P- patients ( P = 0.2980, P = 0.9044; respectively). Higher HPT and lower mechanical detection threshold were related to NeP. This study pointed out the relevance of intraindividual comparisons including mirror areas when assessing local changes in peripheral NeP.

Pharmacological treatments of neuropathic pain: real-life comparisons using propensity score matching

ABSTRACT

Studies comparing different drug treatments for chronic neuropathic pain (NP) are very limited. We, therefore, examined 4 recommended treatments, namely, antidepressants (duloxetine, venlafaxine, and tricyclic antidepressants), antiepileptics (gabapentine and pregabalin), weak opioids, and strong opioids, among patients with NP evaluated before first visit in a tertiary pain treatment centre and 6 months later. Patients with both a clinical diagnosis of NP and a DN4 score ≥3/7 were selected from patients enrolled in the Quebec Pain Registry. Each participant was assigned an inverse weighting of the probability of receiving any NP treatment, taking into account their age, sex, baseline pain intensity, pain duration, pain catastrophizing tendency, education level, employment, and comedications at 6-month follow-up (M6). Patients were considered as improved if they presented at least a 30% reduction on average pain intensity at M6 compared with baseline. A total of 944 patients completed both baseline and M6 evaluations. Overall, 23.0% of patients were significantly improved for pain intensity at M6. There was no significant difference in proportions patients taking or not antidepressants, gabapentinoids, or weak opioids. Among patients taking strong opioids (N = 288), 13.9% (N = 40/288) were improved vs 27.0% (177/656) of those who were not on opioids (P < 0.004). Inverse probability of treatment weighting confirmed that the proportion of patients who improved was significantly lower among those taking strong opioids compared with those who did not (P < 0.001). In conclusion, long-term use of strong opioids is a treatment suited for a limited proportion of patients with chronic NP.

French guidelines for neuropathic pain: An update and commentary

Neuropathic pain remains a significant unmet need. French recommendations were updated in 2020. The goal of this minireview is to provide an update on these published guidelines. Despite newer relevant studies, our proposed algorithm remains relevant. First-line treatments include serotonin-noradrenaline reuptake inhibitors (duloxetine and venlafaxine), gabapentin and tricyclic antidepressants, topical lidocaine and transcutaneous electrical nerve stimulation being specifically proposed for focal peripheral neuropathic pain. Second-line treatments include pregabalin (such position being confirmed by newer studies), tramadol, combinations and psychotherapy as add on, high-concentration capsaicin patches and botulinum toxin A being proposed specifically for focal peripheral neuropathic pain. Third-line treatments include high-frequency repetitive transcranial magnetic stimulation of the motor cortex, spinal cord stimulation and strong opioids (in the lack of alternative). Disseminating these recommendations and ensuring that they are well accepted by French practitioners will be necessary to optimize neuropathic pain management in real life.

Advances in the treatment of neuropathic pain

PURPOSE OF REVIEW

Neuropathic pain remains difficult to treat. This review provides an update regarding recent advances in therapeutic management, particularly with regards to newer drugs, neurostimulation techniques and original study designs.

RECENT FINDINGS

Although the mainstay of neuropathic pain management is still represented by drug therapy, particularly antidepressants and antiepileptics, the place of nonpharmacological therapy including in particular brain neuromodulation techniques has substantially increased in recent years. Newer study designs are also increasingly implemented, based on in depth phenotypic profiling to achieve more individualized therapy, or on screening strategies to decrease placebo effect and contribute to increase assay sensitivity. These approaches are now considered the most promising to decrease therapeutic failures in neuropathic pain.

SUMMARY

Neuropathic pain management should not be restricted to pharmacotherapy but now encompasses multiple approaches including particularly neuromodulation techniques. Multimodal assessment can also help identify predictors of the response in clinical trials in order to ensure appropriate management.

Pharmacotherapeutic Options for Managing Neuropathic Pain: A Systematic Review and Meta-Analysis

Despite an increasing number of available therapies, the treatment of neuropathic pain remains a major issue. Systematic reviews and meta-analyses indicate that only a minority of patients with neuropathic pain have an adequate response to pharmacological treatment and that most drugs have dose-limiting side effects. We conducted a systematic review and meta-analysis of randomised controlled trials published in the last five years. We searched for relevant papers within PubMed, EMBASE, the Cochrane Database of Systematic Reviews, and the Clinical Trials database (ClinicalTrials.gov). Two authors independently selected studies for inclusion, data extraction, and bias assessment. We identified 39 randomised controlled trials and included 16 in the meta-analysis. Trial outcomes were generally modest even for first-line drugs such as tricyclic antidepressants, serotonin-noradrenaline reuptake inhibitors, and gabapentinoids. Many drugs acting on new pain targets are currently under development. Clinical data are currently available for sodium channel isoform-specific antagonists, anti-nerve growth factor molecules, and fatty acid amide hydrolase inhibitors.