Neuropathic pain: a narrative review of etiology, assessment, diagnosis, and treatment for primary care providers

Rethinking neck-related arm pain: hypothetical clinical scenarios to differentiate the underlying IASP-defined pain mechanisms

Neck-related arm pain is frequently encountered in clinical settings, yet its underlying pain mechanisms remain elusive. While such pain radiating from the neck to the arm is often attributed to injuries or diseases of the nervous system (neuropathic pain), it can also arise from nociceptive (referred) or nociplastic sources. Regrettably, patients exhibiting this specific pain distribution are frequently diagnosed with varying terms, including 'cervicobrachialgia', 'cervicobrachial neuralgia', 'cervicobrachial pain syndrome', and 'cervical radiculopathy'. The ambiguity surrounding these diagnostic labels complicates the clinical reasoning process. It is imperative for clinicians to discern and comprehend the dominant pain mechanism. Three distinct hypothetical clinical scenarios depict patients with almost identical pain distribution but divergent dominant pain mechanisms. Within these scenarios, both subjective and objective examinations are employed to elucidate the dominant pain mechanism associated with neck-related arm pain: nociceptive, neuropathic, and nociplastic. Furthermore, clinicians must remain aware that the dominant pain mechanism can evolve over time.

What's New in Neuropathy?

Neuropathic pain presents diagnostic and treatment challenges. Despite recent advances in our understanding of the diagnosis and treatment of neuropathy, much remains to be elucidated. Familiar with neuropathy is the paradox that aberrant nerve signaling causes both sensory loss and pain. Voltage-gated sodium channels play an important role in neuronal electrogenesis and communication among neurons, and their dysregulation leads to hyperexcitability and pain. While numerous validated diagnostic assessment tools are available for neuropathy, patients often experience a diagnostic delay about the cause of their neuropathy. New research is defining more specific types of neuropathy beyond peripheral and central forms. The prevalence of pain varies by type of neuropathy, with chronic idiopathic axonal polyneuropathy associated with the highest proportion of patients experiencing pain. In the majority of types, it exceeds 50%. Gluten neuropathy, a form of peripheral neuropathy, is a new diagnostic consideration. It may require electrochemical conductance testing of hands and feet to test for sudomotor dysfunction. Among those with serologically confirmed gluten sensitivity or celiac disease, gluten neuropathy is a common neurological manifestation and may be addressed at least partially by a gluten-free diet. In Greece, a new neuropathic pain registry was created in 2014 in order to help gather data from real-world neuropathic pain patients. While still in its earliest phase, this registry has already produced demographic and treatment data that suggest suboptimal prescribing and less than recommended use of interventional procedures. Awareness campaigns are underway to encourage more Greek pain clinics to participate in this important registry.

New Vistas in microRNA Regulatory Interactome in Neuropathic Pain

Neuropathic pain is a chronic pain condition seen in patients with diabetic neuropathy, cancer chemotherapy-induced neuropathy, idiopathic neuropathy as well as other diseases affecting the nervous system. Only a small percentage of people with neuropathic pain benefit from current medications. The complexity of the disease, poor identification/lack of diagnostic and prognostic markers limit current strategies for the management of neuropathic pain. Multiple genes and pathways involved in human diseases can be regulated by microRNA (miRNA) which are small non-coding RNA. Several miRNAs are found to be dysregulated in neuropathic pain. These miRNAs regulate expression of various genes associated with neuroinflammation and pain, thus, regulating neuropathic pain. Some of these key players include adenylate cyclase (Ac9), toll-like receptor 8 (Tlr8), suppressor of cytokine signaling 3 (Socs3), signal transducer and activator of transcription 3 (Stat3) and RAS p21 protein activator 1 (Rasa1). With advancements in high-throughput technology and better computational power available for research in present-day pharmacology, biomarker discovery has entered a very exciting phase. We dissect the architecture of miRNA biological networks encompassing both human and rodent microRNAs involved in the development of neuropathic pain. We delineate various microRNAs, and their targets, that may likely serve as potential biomarkers for diagnosis, prognosis, and therapeutic intervention in neuropathic pain. miRNAs mediate their effects in neuropathic pain by signal transduction through IRAK/TRAF6, TLR4/NF-κB, TXIP/NLRP3 inflammasome, MAP Kinase, TGFβ and TLR5 signaling pathways. Taken together, the elucidation of the landscape of signature miRNA regulatory networks in neuropathic pain will facilitate the discovery of novel miRNA/target biomarkers for more effective management of neuropathic pain.

Approach to Neuropathic Pain

Neuropathic pain is a common chief complaint encountered by neurologists and primary care providers. It is caused by disorders involving the somatosensory nervous system. The clinical evaluation of neuropathic pain is challenging and requires a multifaceted systematic approach with an emphasis on a thorough history and physical examination to identify characteristic signs and symptoms. Ancillary laboratory investigations, targeted imaging, and electrodiagnostic studies further help identify underlying etiologies to guide specific treatments. Management of neuropathic pain encompasses treating the underlying pathology as well as symptomatic control with nonpharmacological, pharmacological, and interventional therapies. Here, we present an approach to help evaluate patients with neuropathic pain.

Methods to discriminate between mechanism-based categories of pain experienced in the musculoskeletal system: a systematic review

ABSTRACT

Mechanism-based classification of pain has been advocated widely to aid tailoring of interventions for individuals experiencing persistent musculoskeletal pain. Three pain mechanism categories (PMCs) are defined by the International Association for the Study of Pain: nociceptive, neuropathic, and nociplastic pain. Discrimination between them remains challenging. This study aimed to build on a framework developed to converge the diverse literature of PMCs to systematically review methods purported to discriminate between them; synthesise and thematically analyse these methods to identify the convergence and divergence of opinion; and report validation, psychometric properties, and strengths/weaknesses of these methods. The search strategy identified articles discussing methods to discriminate between mechanism-based categories of pain experienced in the musculoskeletal system. Studies that assessed the validity of methods to discriminate between categories were assessed for quality. Extraction and thematic analysis were undertaken on 184 articles. Data synthesis identified 200 methods in 5 themes: clinical examination, quantitative sensory testing, imaging, diagnostic and laboratory testing, and pain-type questionnaires. Few methods have been validated for discrimination between PMCs. There was general convergence but some disagreement regarding findings that discriminate between PMCs. A combination of features and methods, rather than a single method, was generally recommended to discriminate between PMCs. Two major limitations were identified: an overlap of findings of methods between categories due to mixed presentations and many methods considered discrimination between 2 PMCs but not others. The results of this review provide a foundation to refine methods to differentiate mechanisms for musculoskeletal pain.

MCRT, a multifunctional ligand of opioid and neuropeptide FF receptors, attenuates neuropathic pain in spared nerve injury model

Chimeric peptide MCRT (YPFPFRTic-NH₂ ) was a multifunctional ligand of opioid and neuropeptide FF (NPFF) receptors and reported to be potentially antalgic in acute tail-flick test. Here, we developed spared nerve injury (SNI) model to explore its efficacy in chronic neuropathic pain. Analgesic tolerance, opioid-induced hyperalgesia and gastrointestinal transit were measured for safety evaluation. Intracerebroventricular (i.c.v.) and intraplantar (i.pl.) injections were conducted as central and peripheral routes, respectively. Results demonstrated that MCRT alleviated neuropathic pain effectively and efficiently, with the ED₅₀ values of 4.93 nmol/kg at the central level and 3.11 nmol/kg at the peripheral level. The antagonist blocking study verified the involvement of mu-, delta-opioid and NPFF receptors in MCRT produced anti-allodynia. Moreover, the separation of analgesia from unwanted effects was preliminarily achieved and that MCRT caused neither analgesic tolerance nor hyperalgesia after chronic i.c.v. administration, nor constipation after i.pl. administration. Notably, the local efficacy of MCRT in SNI mice was about one thousandfold higher than morphine and ten thousandfold higher than pregabalin, indicating a great promise in the future treatment of neuropathic pain.

Statins and Neuropathic Pain: A Narrative Review

The frequently prescribed drug class of statins have pleiotropic effects and have been implicated in neuropathic pain syndromes. This narrative review examines studies of statin-induced neuropathic pain which to date have been conducted only in animal models. However, the pathophysiology of diabetic neuropathy in humans may shed some light on the etiology of neuropathic pain. Statins have exhibited a paradoxical effect in that statins appear to reduce neuropathic pain in animals but have been associated with neuropathic pain in humans. While there are certain postulated mechanisms offering elucidation as to how statins might be associated with neuropathic pain, there is, as the American Heart Association stated, to date no definitive association between statins and neuropathic pain. Statins are important drugs that reduce cardiovascular risk factors and should be prescribed to appropriate patients with these risk factors but some of this population is also at elevated risk for neuropathic pain from other causes.

Emerging role of nanomedicine in the treatment of neuropathic pain

Neuropathic pain (NeP) is a complex chronic pain condition associated with nerve injury. Approximately, 7-10% of the general population across the globe is suffering from this traumatic condition, but the existing treatment strategies are inadequate to deliver pain relief and are associated with severe adverse effects. To overcome these limitations, lot of research is focussed on developing new molecules with high potency and fewer side effects, novel cell and gene-based therapies and modification of the previously approved drugs by different formulation aspects. Nanomedicine has attracted a lot of attention in the treatment of many diverse pathological conditions because of their unique physiochemical and biological properties. In this manuscript, we highlighted the emerging role of nanomedicine in different therapies (drug, cell and gene), also we emphasised on the challenges associated with nanomedicine such as development of well-characterised nanoformulation, scaling of batches with reproducible results and toxicity along with this we discussed about the future of nanomedicine in the treatment of neuropathic pain.

Gabapentin versus Transdermal Fentanyl Matrix for the Alleviation of Chronic Neuropathic Pain of Radicular Origin: A Randomized Blind Multicentered Parallel-Group Noninferiority Trial

A number of studies have been published proposing various approaches to the treatment of neuropathic pain; however, to our knowledge, no attempts have been made to compare gabapentin and fentanyl in patients with lumbar radiculopathy. We evaluated the relative efficacy and safety of fentanyl matrix and gabapentin for the treatment of chronic neuropathic pain of radicular origin. The study was designed as a randomized blind multicentered parallel-group noninferiority trial. A total of 108 patients with moderate-to-severe pain (≥4 intensity on an 11-point numeric rating scale) were randomly prescribed either fentanyl matrix or gabapentin over a period of 56 days. In the primary analysis, the noninferiority of fentanyl matrix treatment was evaluated in relation to the efficacy of gabapentin based on the pain intensity difference (PID) at 56 days after the first dose of the drugs. Secondary endpoints included pain relief, improvement in functional status (the Korean-Oswestry Disability Index (K-ODI)), improvement in depressive symptoms (Korean-Beck Depression Index (K-BDI)) between the 28th and 56th day, and adverse events (AEs). Analysis of the primary efficacy endpoint established the noninferiority of fentanyl matrix compared with gabapentin, with no statistically significant difference observed in the PID after 56 days for the two treatment groups. Similarly, analysis of pain relief revealed no significant differences between the groups on days 28 and 56. There was no difference in the K-ODI and K-BDI between the groups during the study period. The overall incidence of at least one AE was similar for fentanyl matrix (67.3%) and gabapentin (69.6%). The most commonly reported AEs for patients treated with fentanyl matrix and gabapentin included dizziness (30.8% vs. 44.6%, respectively), somnolence (26.9% vs. 35.7%), and constipation (15.4% vs. 17.9%). This study demonstrated that the analgesic effect of fentanyl matrix is noninferior in comparison with gabapentin and supports the use of fentanyl matrix as an effective and safe treatment for moderate-to-severe chronic neuropathic pain. This trial is registered with NCT01127100.

Whole body vibration exercise in the management of cancer therapy-related morbidities: A systematic review

The purpose of this systematic review was to investigate the effects of whole body vibration (WBV) exercise in the management of cancer therapy-related morbidities. The PubMED and PEDro databases were used to access publications published in English about the use of whole body vibration (WBV) exercises in cancer patients until February 22^nd 2017. The studies included were classified according to the level of evidence (LE) by the National Health and Medical Research Council Hierarchy of evidence and the methodological quality (MQ) by the PEDro scale. The four included studies (2 of them with "high" LE-II and MQ) were performed in patients with different types of cancer (i.e. breast, lung, prostate, solid or hematological), treated with WBV exercise to counteract the cancer therapy-related morbidities. The variables evaluated were muscle activity, subjective rate of perceived exertion, exercise capacity, muscle strength, quality of life, resting urinary incontinence and severity of peripheral neuropathy. Although WBV exercise appears to be a potential treatment procedure of cancer therapy-related morbidities, further additional studies are required to determine specific and tailored protocols to be used in the different stages of the disease.

Pregabalin for the treatment of neuropathic pain: a narrative review for primary care providers

BACKGROUND

Neuropathic pain (NeP) is a distinct type of pain caused by damage to the nervous system itself. This often severe and chronic type of pain requires specific treatments that target the underlying pain pathophysiology.

AIM

The purpose of the current narrative review is to provide an overview of pregabalin (Lyrica ¹ ) for the treatment of NeP including its effects on pain, pain-related sleep interference, and other health-related outcomes, timing of therapeutic effect, safety and tolerability, and dosing. The information provided here will help primary care providers develop more effective NeP treatment strategies.