Epidemiology of neuropathic pain

Antinociceptive Effect of the Combination of a Novel α4β2* Agonist with Donepezil in a Chronic Pain Model

Chronic pain presents a major challenge in contemporary medicine, given the limited effectiveness and numerous adverse effects linked to available treatments. Recognizing the potential of the cholinergic pathway as a therapeutic target, the present work evaluates the antinociceptive activity of a combination of Cris-104, a novel α4β2* receptor agonist, and donepezil, a central anticholinesterase agent. Isobolographic analysis revealed that equimolar combination was approximately 10 times more potent than theoretically calculated equipotent additive dose. Administration of Cris-104 and donepezil combination (3 μmol/kg) successfully reversed hyperalgesia and mechanical allodynia observed in rats subjected to spinal nerve ligation (SNL). The combination also modulated neuroinflammation by reducing astrocyte activation, evident in the decreased expression of glial fibrillary acidic protein (GFAP) in the spinal cord. The observed synergism in combining a nicotinic receptor agonist with an anticholinesterase agent underscores its potential for treating chronic pain. This alternative therapeutic distinct advantage, including dose reduction and high selectivity for the receptor, contribute to a more favorable profile with minimized adverse effects.

Considerations on the Obstacles That Lead to Slow Recruitment in a Pain Management Clinical Trial: Experiences from the Belgian PELICAN (PrEgabalin Lidocaine Capsaicin Neuropathic Pain) Pragmatic Study

Background

A qualitative evaluation study of the prematurely terminated PrEgabalin Lidocaine Capsaicin Neuropathic Pain (PELICAN) study was performed. The PELICAN study aimed to examine pain management for localized neuropathic pain (LNP), as epidemiological figures have shown a high percentage of LNP patients in Belgium. The study compared systemic and topical medications according to pain relief, adverse effects, and several measures of quality of life.

Objective

Achieving better study patient recruitment through qualitative research. To investigate and determine the causes of the observed recruitment problems in the PELICAN study, pain centers involved in the study as well as nonrecruiting pain centers were included. Furthermore, it aimed to highlight the positive and negative lessons learned from the conducted study and the number of obstacles the team had to overcome.

Methods

A qualitative study, using a mixed methods approach, was performed. Multiple pain centers in Belgium completed an online survey, after which a structured interview was conducted to elaborate the responses in more detail. The broad topics of these meetings were feedback about the study, reviewing survey answers, and actions undertaken to enhance recruitment.

Results

Different factors contributed to the low recruitment rate in the PELICAN study, such as limited and late referral from the general practitioners to the Belgian pain centers, insufficient internal referrals from nonpain specialists, lack of specific expertise on LNP in some centers, scarcity of staff, limited reimbursement to administer complex analgesic schemes, overestimation of the patient population, and the reluctance of patients to participate in pain research. Additionally, shortcomings in the implemented study design and the need for more logistical investments were identified.

Conclusion

The findings of the qualitative study demonstrate the need for further, more varied LNP research in Belgium, not limited to pharmacological studies. It also sheds important light on the recruitment obstacles that may be faced during these studies. Future studies could support this research by offering better proposals for feasibility and recruitment, for instance, by designing and conducting a compelling pilot study or applying social media during the recruitment phase. Clinical Trials. This trial is registered with NCT03348735. EUDRACT number 2018-003617-17.

A Review of Scientific Evidence for THC:CBD Oromucosal Spray (Nabiximols) in the Management of Chronic Pain

The 20% prevalence of chronic pain in the general population is a major health concern given the often profound associated impairment of daily activities, employment status, and health-related quality of life in sufferers. Resource utilization associated with chronic pain represents an enormous burden for healthcare systems. Although analgesia based on the World Health Organization’s pain ladder continues to be the mainstay of chronic pain management, aside from chronic cancer pain or end-of-life care, prolonged use of non-steroidal anti-inflammatory drugs or opioids to manage chronic pain is rarely sustainable. As the endocannabinoid system is known to control pain at peripheral, spinal, and supraspinal levels, interest in medical use of cannabis is growing. A proprietary blend of cannabis plant extracts containing delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) as the principal cannabinoids is formulated as an oromucosal spray (USAN name: nabiximols) and standardized to ensure quality, consistency and stability. This review examines evidence for THC:CBD oromucosal spray (nabiximols) in the management of chronic pain conditions. Cumulative evidence from clinical trials and an exploratory analysis of the German Pain e-Registry suggests that add-on THC:CBD oromucosal spray (nabiximols) may have a role in managing chronic neuropathic pain, although further precise clinical trials are required to draw definitive conclusions.

G-Protein Coupled Receptors Targeted by Analgesic Venom Peptides

Chronic pain is a complex and debilitating condition associated with a large personal and socioeconomic burden. Current pharmacological approaches to treating chronic pain such as opioids, antidepressants and anticonvulsants exhibit limited efficacy in many patients and are associated with dose-limiting side effects that hinder their clinical use. Therefore, improved strategies for the pharmacological treatment of pathological pain are urgently needed. G-protein coupled receptors (GPCRs) are ubiquitously expressed on the surface of cells and act to transduce extracellular signals and regulate physiological processes. In the context of pain, numerous and diverse families of GPCRs expressed in pain pathways regulate most aspects of physiological and pathological pain and are thus implicated as potential targets for therapy of chronic pain. In the search for novel compounds that produce analgesia via GPCR modulation, animal venoms offer an enormous and virtually untapped source of potent and selective peptide molecules. While many venom peptides target voltage-gated and ligand-gated ion channels to inhibit neuronal excitability and blunt synaptic transmission of pain signals, only a small proportion are known to interact with GPCRs. Of these, only a few have shown analgesic potential in vivo. Here we review the current state of knowledge regarding venom peptides that target GPCRs to produce analgesia, and their development as therapeutic compounds.

Trends in long-term opioid prescribing in primary care patients with musculoskeletal conditions: an observational database study

Supplemental Digital Content is Available in the Text.

Long-term opioid use decreased from 2011, but the proportion of more potent opioids prescribed increased. Ongoing review of effectiveness and need for discontinuation is important.

Long-term opioids may benefit patients with chronic pain but have also been linked to harmful outcomes. In the United Kingdom, the predominant source of opioids is primary care prescription. The objective was to examine changes in the incidence, length, and opioid potency of long-term prescribing episodes for musculoskeletal conditions in UK primary care (2002-2013). This was an observational database study (Clinical Practice Research Datalink, 190 practices). Participants (≥18 years) were prescribed an opioid for a musculoskeletal condition (no opioid prescribed in previous 6 months), and issued ≥2 opioid prescriptions within 90 days (long-term episode). Opioids were divided into short- and long-acting noncontrolled and controlled drugs. Annual incidence of long-term opioid episodes was determined, and for those still in a long-term episode, the percentage of patients prescribed each type 1 to 2 years, and >2 years after initiation. Annual denominator population varied from 1.25 to 1.38 m. A total of 76,416 patients started 1 long-term episode. Annual long-term episode incidence increased (2002-2009) by 38% (42.4-58.3 per 10,000 person-years), remaining stable to 2011, then decreasing slightly to 55.8/10,000 (2013). Patients prescribed long-acting controlled opioids within the first 90 days of long-term use increased from 2002 to 2013 (2.3%-9.9%). In those still in a long-term opioid episode (>2 years), long-acting controlled opioid prescribing increased from 3.5% to 22.6%. This study has uniquely shown an increase in prescribing long-term opioids to 2009, gradually decreasing from 2011 in the United Kingdom. The trend was towards increased prescribing of controlled long-acting opioids and earlier use. Further research into the risks and benefits of opioids is required.

Is an easy and reliable diagnosis of localized neuropathic pain (LNP) possible in general practice? Development of a screening tool based on IASP criteria

BACKGROUND AND OBJECTIVE

Neuropathic pain (NP) is a common type of chronic pain in which 60% of patients present with localized symptoms. Early diagnosis of NP is often a challenge in primary care. Moreover, so far no standard diagnostic procedure for localized NP (LNP) is available. To help general practitioners, a screening tool was developed and evaluated.

RESEARCH DESIGN AND METHODS

The development of the screening tool was based on the grading system principles for NP proposed by the IASP, focusing on medical history and distribution of painful symptoms and sensory signs. It was tested by 31 general practitioners and evaluated against the NP diagnosis of three pain specialists as reference in a single center prospective study in Spain using a cohort study design including an adult population of chronic pain patients. This design avoids spectrum bias where the spectrum of disease is not correctly reflected in the study population.

MAIN OUTCOME MEASURES

General practitioners rated usefulness, simplicity, and time requirements of the tool. Diagnostic accuracy was expressed by sensitivity, specificity, and positive and negative predictive values.

RESULTS

General practitioners consecutively screened 2079 chronic pain patients (mean age 60.7 ± 11.1 years, 69.9% female). Using the tool, 394 patients were diagnosed with LNP. Screening including sensory examination took 7 min (median). General practitioners rated the tool as useful (24/31; 77.4%) or very useful (7/31; 22.6%) for diagnosing LNP and facilitating clinical practice (30/31; 96.8%). Under daily practice conditions, sensitivity and specificity of the tool for detecting LNP was 46.7% and 86.6%, respectively.

CONCLUSIONS

The proposed screening tool was shown to be easy and useful for detecting NP and LNP in chronic pain patients as a fast first assessment tool in primary care, thus facilitating the choice of a topical treatment. LIMITATIONS AND STRENGTHS: The drop-out rate was high but was accounted for by using correction factors in the diagnostic accuracy calculations. A strength is the unselected chronic patient population: spectrum of disease correctly reflects day-to-day clinical practice and is not biased. Diagnostic accuracy of the tool therefore appears to be realistic.

Ask the Experts: Neuropathic pain from a primary care perspective

Blair H Smith, MD, MEd, FRCGP, FRCP, Edin, qualified in medicine at the University of Glasgow (Scotland, UK) in 1987, and as a general practitioner in 1993. He is the Professor of Population Science at the University of Dundee (Scotland, UK), having previously been the Professor of Primary Care Medicine at the University of Aberdeen (Scotland, UK). He is also a general practitioner with the Peterhead Medical Practice (Aberdeenshire, Scotland, UK). His research on the epidemiology and primary care management of chronic (neuropathic) pain has been widely published with more than 100 original research articles in peer-reviewed medical journals, and numerous related book chapters. He leads a program of research, funded by the UK Medical Research Council, on the selfmanagement of chronic pain by older adults, and is also one of the Chief Investigators in Generation Scotland, a major family study for research into the genetics of health and illness, including pain. He is currently the Treasurer of the Neuropathic Pain Special Interest Group of the International Association for the Study of Pain and Director of the Scottish Pain Research Community.

Can treatment success with 5% lidocaine medicated plaster be predicted in cancer pain with neuropathic components or trigeminal neuropathic pain?

An expert group of 40 pain specialists from 16 countries performed a first assessment of the value of predictors for treatment success with 5% lidocaine-medicated plaster in the management of cancer pain with neuropathic components and trigeminal neuropathic pain. Results were based on the retrospective analysis of 68 case reports (sent in by participants in the 4 weeks prior to the conference) and the practical experience of the experts. Lidocaine plaster treatment was mostly successful for surgery or chemotherapy-related cancer pain with neuropathic components. A dose reduction of systemic pain treatment was observed in at least 50% of all cancer pain patients using the plaster as adjunct treatment; the presence of allodynia, hyperalgesia or pain quality provided a potential but not definitively clear indication of treatment success. In trigeminal neuropathic pain, continuous pain, severe allodynia, hyperalgesia, or postherpetic neuralgia or trauma as the cause of orofacial neuropathic pain were perceived as potential predictors of treatment success with lidocaine plaster. In conclusion, these findings provide a first assessment of the likelihood of treatment benefits with 5% lidocaine-medicated plaster in the management of cancer pain with neuropathic components and trigeminal neuropathic pain and support conducting large, well-designed multicenter studies.

Epidemiology of neuropathic pain and its impact on quality of life

Epidemiology is an important clinical tool in designing and evaluating management and prevention strategies, and is particularly relevant to neuropathic pain. However, there is a relative lack of accurate information available. In one sense, neuropathic pain describes a symptom or a mechanism, rather than a specific disease; on the other hand, there are sufficient similarities in the effects and response to treatment between different causes to make it worthwhile to consider neuropathic pain as a distinct condition. However, there are important specific disease-based factors that need to be considered separately. Estimates of prevalence that are based on specific causes of neuropathic pain tend to be lower (1-2%) than those that are based on reports of the classic symptoms (6-8%), and further methodological research is needed. All neuropathic pain is associated with poor general health, comparable with other severe chronic diseases. The importance of newly proposed risk factors, including genetic factors, still needs to be assessed at a population level.

Treatment of localized neuropathic pain after disk herniation with 5% lidocaine medicated plaster

Objective

To assess treatment with the 5% lidocaine medicated plaster for peripheral neuropathic pain after disk herniation.

Study design

Case series, single center, retrospective data.

Patients and methods

Data of 23 patients treated for neuropathic pain with the lidocaine plaster for up to 24 months after a protrusion or prolapse of the cervical, thoracic, or lumbar vertebral disks were retrospectively analyzed. Changes in overall pain intensity, in intensity of different pain qualities and of allodynia and hyperalgesia were evaluated.

Results

Patients (14 female/nine male, mean age 53.5 ± 10.4 years) presented with radiating pain into the abdomen, back, neck, shoulder, or legs and feet with a mean pain intensity of 8.3 ± 1.5 on the 11-point Likert scale. Mean treatment duration was 7.6 months; 52% of the patients received lidocaine plaster as monotherapy. At the end of the observation, mean overall pain intensity had been reduced to 3.1 ± 1.8. All other parameters also improved. The treatment was well tolerated.

Conclusion

These results point to a safe and effective treatment approach with 5% lidocaine medicated plaster for localized neuropathic pain related to disk herniation. However, owing to the small sample size, further investigation in a larger-scale controlled trial is warranted.

Prevalence of neuropathic features of back pain in clinical populations: implications for the diagnostic triage paradigm

SUMMARY Contemporary clinical assessment of back pain is based on the diagnostic triage paradigm. The most common diagnostic classification is nonspecific back pain, considered to be of nociceptive etiology. A small proportion are diagnosed with radicular pain, of neuropathic origin. In this study we review the body of literature on the prevalence of neuropathic features of back pain, revealing that the point prevalence is 17% in primary care, 34% in mixed clinical settings and 53% in tertiary care. There is evidence that neuropathic features of back pain are not restricted to typical clinical radicular pain phenotypes and may be under-recognized, particularly in primary care. The consequence of this is that in the clinic, diagnostic triage may erroneously classify patients with nonspecific back pain or radicular pain. A promising alternative is the development of mechanism-based pain phenotyping in patients with back pain. Timely identification of contributory pain mechanisms may enable greater opportunity to select appropriate therapeutic targets and improve patient outcomes.

Patient perceptions associated with the 5% lidocaine medicated plaster in daily practice

OBJECTIVE

To evaluate patients' perceptions of 5% lidocaine medicated plaster for treatment of chronic neuropathic pain in daily clinical practice.

RESEARCH DESIGN AND METHODS

In a prospective, multicentre, non-interventional observation, patient-reported outcome data were collected in clinical practices in Germany using the German Pain Questionnaire for pre-treatment documentation and the German Pain Diary for documentation of weekly treatment-associated changes. Questionnaires were completed by the patients without input from their physicians.

MAIN OUTCOME MEASURES

Mean changes over the 12-week treatment period in pain intensity, in impairments of daily activities (modified pain disability index, mPDI) and of quality of life (quality of life impairment by pain inventory, QLIP), in Hospital Anxiety and Depression Scale scores (HADS-A and HADS-D), and in overall burden of pain.

RESULTS

Data of 922 patients were evaluated. Mean average pain intensity over 24 h improved by 5.1 points (74%) from 6.9 ± 1.6 points at baseline. A 30% reduction in overall pain intensity was already observed within the first 2-3 weeks with continuous further reductions until end of observation. Marked improvements in anxiety and depression scores (40% and 52%, respectively), and in pain-related restrictions in daily life activities (66%) and quality of life (157%) were also noted. Burden of pain was reduced by 56.2 points (73%) from 77.5 points at baseline. Stratification by diagnosis showed a treatment effect of lidocaine plaster for all underlying conditions with highest treatment effects for diabetic polyneuropathy and postherpetic neuralgia.

CONCLUSIONS

In a patient population where 46% of individuals already suffered from chronic to markedly chronic pain, patients perceive the 5% lidocaine medicated plaster as an efficacious topical treatment of chronic neuropathic pain in daily clinical practice. Strongest pain relief as well as associated improvements in pain-related restrictions were observed within the first five treatment weeks; however, beneficial effects continued until end of observation.

Towards a definition of refractory neuropathic pain for epidemiological research. An international Delphi survey of experts

Background

Best current estimates of neuropathic pain (NeuP) prevalence come from studies using various screening detecting pain with probable neuropathic features; the proportion experiencing significant, long-term NeuP, and the proportion not responding to standard treatment are unknown. These “refractory” cases are the most clinically important to detect, being the most severe, requiring specialist treatment.

Methods

We report an international Delphi survey of experts in NeuP, aiming for consensus on the features required to define, for epidemiological research: (1) neuropathic pain; and (2) when NeuP is “refractory”. A web-based questionnaire was developed and data collected from three rounds of questionnaires from nineteen experts.

Results

There was good consensus on essential inclusion of six items to identify NeuP (“prickling, tingling, pins & needles”, “pain evoked by light touch”, “electric shocks or shooting pain”, “hot or burning” pain, “brush allodynia on self-examination”, and “relevant history”) and on some items that were non-essential. Consensus was also reached on components of a “refractory NeuP” definition: minimum duration (one year); number of trials of drugs of known effectiveness (four); adequate duration of these trials (three months / maximum tolerated); outcomes of treatment (pain severity, quality of life). Further work needs to validate these proposed criteria in general population research.

Conclusions

This paper presents an international consensus on measuring the epidemiology of refractory neuropathic pain. This will be valuable in reaching an agreed estimate of the prevalence of neuropathic pain, and the first estimate of refractory neuropathic pain prevalence.

What is localized neuropathic pain? A first proposal to characterize and define a widely used term

SUMMARY According to several guidelines, topical agents should be considered for the pharmacological management of localized neuropathic pain. As a definition for the term ‘localized neuropathic pain’ that might facilitate easier identification of patients who are putatively responsive to topical treatments could not be found in the literature, six pain specialists met in 2010 to address this challenging issue. The following nucleus of a definition that is based on the International Association for the Study of Pain (IASP) definition of neuropathic pain, is the most detailed that can currently be proposed: ‘Localized neuropathic pain is a type of neuropathic pain that is characterized by consistent and circumscribed area(s) of maximum pain’. An extended version of this core definition and the difficulties in covering all aspects of localized neuropathic pain are presented, and discussions within the scientific community are encouraged to develop a definition that might help to identify patients who could benefit most from topical treatment.