Chronification of Pain: Mechanisms, Current Understanding, and Clinical Implications

2022 AAHA Pain Management Guidelines for Dogs and Cats

These updated guidelines present a practical and logical approach to the assessment and management of acute and chronic pain in canine and feline patients. Recognizing pain is fundamental to successful treatment, and diagnostic guides and algorithms are included for assessment of both acute and chronic pain. Particularly for chronic pain, capturing owner evaluation is important, and pain-assessment instruments for pet owners are described. Expert consensus emphasizes proactive, preemptive pain management rather than a reactive, "damage control" approach. The guidelines discuss treatment options centered on preemptive, multimodal analgesic therapies. There is an extensive variety of pharmacologic and nonpharmacologic therapeutic options for the management of acute and chronic pain in cats and dogs. The guidelines include a tiered decision tree that prioritizes the use of the most efficacious therapeutic modalities for the treatment of acute and chronic pain.

Novel bivalent ligands carrying potential antinociceptive effects by targeting putative mu opioid receptor and chemokine receptor CXCR4 heterodimers

The functional interactions between opioid and chemokine receptors have been implicated in the pathological process of chronic pain. Mounting studies have indicated the possibility that a MOR-CXCR4 heterodimer may be involved in nociception and related pharmacologic effects. Herein we have synthesized a series of bivalent ligands containing both MOR agonist and CXCR4 antagonist pharmacophores with an aim to investigate the functional interactions between these two receptors. In vitro studies demonstrated reasonable recognition of designed ligands at both respective receptors. Further antinociceptive testing in mice revealed compound 1a to be the most promising member of this series. Additional molecular modeling studies corroborated the findings observed. Taken together, we identified the first bivalent ligand 1a showing promising antinociceptive effect by targeting putative MOR-CXCR4 heterodimers, which may serve as a novel chemical probe to further develop more potent bivalent ligands with potential application in analgesic therapies for chronic pain management.

Pain in Persons with Disorders of Consciousness

Pain and suffering in persons with disorders of consciousness (DoC) remain poorly understood, frequently unaddressed or inadequately addressed, and controversial on numerous levels. This narrative literature review will address a number of critical issues germane to pain and suffering in this challenging group of patients, providing an introductory overview of the topic, perspectives on current knowledge regarding pain pathoanatomy and pathophysiology, and a review of common pain generators and factors that can lead to the chronifcation of pain. Caveats on bedside pain assessment challenges, as well as electrophysiologic and neuroimaging findings in these patients, will also be explored. Pain management techniques, including non-pharmacological and pharmacological, will be reviewed. Ethical considerations in the context of pain and suffering in persons with disorders of consciousness will round out the review prior to our concluding comments.

Interactions between Ketamine and Magnesium for the Treatment of Pain: Current State of the Art

BACKGROUND

Over the past three decades, NMDA-receptor antagonists have been shown to be efficient drugs for treating pain, particularly pain resistant to conventional analgesics. Emphasis will be on the old-new drugs, ketamine and magnesium, and their combination as a novel approach for treating chronic pain.

METHODS

The MEDLINE database was searched via PubMed for articles that were published up to March 1, 2020, with the keywords 'ketamine', 'magnesium', and 'pain' (in the title/abstract).

RESULTS

Studies in animals, as well as humans, have shown that interactions of ketamine and magnesium can be additive, antagonistic, and synergistic. These discrepancies might be due to differences in magnesium and ketamine dosage, administration times, and the chronological order of drug administration. Different kinds of pain can also be the source of divergent results.

CONCLUSION

This review explains why studies performed with a combination of ketamine and magnesium have given inconsistent results. Because of the lack of efficacy of drugs available for pain, ketamine and magnesium in combination provide a novel therapeutic approach that needs to be standardized with a suitable dosing regimen, including the chronological order of drug administration.

Effects of Patient and Surgery Characteristics on Persistent Postoperative Pain: A Mediation Analysis

OBJECTIVE

Acute postoperative pain intensity is associated with persistent postsurgical pain (PPP) risk. However, it remains unclear whether acute postoperative pain intensity mediates the relationship between clinical factors and persistent pain.

MATERIALS AND METHODS

Participants from a mixed surgical population completed the Brief Pain Inventory and Pain Catastrophizing Scale before surgery, and the Brief Pain Inventory daily after surgery for 7 days and at 30 and 90 days after surgery. We considered mediation models using the mean of the worst pain intensities collected daily on each of postoperative days (PODs) 1 to 7 against outcomes of worst pain intensity at the surgical site endpoints reflecting PPP (POD 90) and subacute pain (POD 30).

RESULTS

The analyzed cohort included 284 participants for the POD 90 outcome. For every unit increase of maximum acute postoperative pain intensity through PODs 1 to 7, there was a statistically significant increase of mean POD 90 pain intensity by 0.287 after controlling for confounding effects. The effects of female versus male sex (m=0.212, P=0.034), pancreatic/biliary versus colorectal surgery (m=0.459, P=0.012), thoracic cardiovascular versus colorectal surgery (m=0.31, P=0.038), every minute increase of anesthesia time (m=0.001, P=0.038), every unit increase of preoperative average pain score (m=0.012, P=0.015), and every unit increase of catastrophizing (m=0.044, P=0.042) on POD 90 pain intensity were mediated through acute PODs 1 to 7 postoperative pain intensity.

DISCUSSION

Our results suggest the mediating relationship of acute postoperative pain on PPP may be predicated on select patient and surgical factors.

Autogenic Training for Reducing Chronic Pain: a Systematic Review and Meta-analysis of Randomized Controlled Trials

Background

Autogenic training (AT) is frequently used as therapeutic approach in multimodal pain therapy. The aim of this systematic review and meta-analysis is to investigate the efficacy of AT in individuals suffering from chronic pain in comparison to passive and active control groups.

Methods

A comprehensive literature search in Medline, Web of Science, PsycInfo, and PubPsych and manual searches (last search April 7, 2021) were conducted to locate randomized controlled trials (RCTs). Treatment guidelines and references of relevant articles and previous reviews were checked. ProQuest Dissertations and Theses Full Text database, DART-Europe E-theses Portal, Networked Digital Library of Theses and Dissertations (NDLTD), and the Theses Database of the German National Library were screened to identify any unpublished material.

Results

A total of 13 eligible studies (k = 15 comparisons) including 576 participants were identified. Random-effects meta-analyses revealed a significantly positive, moderate effect of AT on the primary outcome pain compared to passive control groups (g = 0.58, 95% CI [0.36; 0.79], k = 9, I² = 0%). In comparison with other psychological interventions, no difference was found (g = − 0.05, 95% CI [− 0.30; 0.20], k = 6, I² = 0%). Sensitivity analyses proved the robustness of findings. Overall risk-of-bias judgment was ‘some concerns’ in the majority of studies.

Conclusions

Beneficial effects of AT on pain reduction were demonstrated, but findings are prone to bias. Furthermore, high methodological quality RCTs are needed to strengthen the promising evidence of AT for individuals with chronic pain.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12529-021-10038-6.

In silico Identification of Key Factors Driving the Response of Muscle Sensory Neurons to Noxious Stimuli

Nociceptive nerve endings embedded in muscle tissue transduce peripheral noxious stimuli into an electrical signal [i.e., an action potential (AP)] to initiate pain sensations. A major contributor to nociception from the muscles is mechanosensation. However, due to the heterogeneity in the expression of proteins, such as ion channels, pumps, and exchangers, on muscle nociceptors, we currently do not know the relative contributions of different proteins and signaling molecules to the neuronal response due to mechanical stimuli. In this study, we employed an integrated approach combining a customized experimental study in mice with a computational model to identify key proteins that regulate mechanical nociception in muscles. First, using newly collected data from somatosensory recordings in mouse hindpaw muscles, we developed and then validated a computational model of a mechanosensitive mouse muscle nociceptor. Next, by performing global sensitivity analyses that simulated thousands of nociceptors, we identified three ion channels (among the 17 modeled transmembrane proteins and four endoplasmic reticulum proteins) as potential regulators of the nociceptor response to mechanical forces in both the innocuous and noxious range. Moreover, we found that simulating single knockouts of any of the three ion channels, delayed rectifier voltage-gated K⁺ channel (Kv1.1) or mechanosensitive channels Piezo2 or TRPA1, considerably altered the excitability of the nociceptor (i.e., each knockout increased or decreased the number of triggered APs compared to when all channels were present). These results suggest that altering expression of the gene encoding Kv1.1, Piezo2, or TRPA1 might regulate the response of mechanosensitive muscle nociceptors.

Persistent Pain After Cardiac Surgery: Prevention and Management

Persistent postoperative pain (PPP) after cardiac surgery is a significant complication that negatively affects patient quality of life and increases health care system burden. However, there are no standards or guidelines to inform how to mitigate these effects. Therefore, in this review, we will discuss strategies to prevent and manage PPP after cardiac surgery. Adequate perioperative analgesia may prove instrumental in the prevention of PPP. Although opioids have historically been the primary analgesic approach to cardiac surgery, an opioid-sparing strategy may prove advantageous in reducing side effects, avoiding secondary hyperalgesia, and decreasing risk of PPP. Implementing a multimodal analgesic plan using alternative medications and regional anesthetic techniques may offer superior efficacy while reducing adverse effects.

Cross-cultural adaptation and validation of the German Central Sensitization Inventory (CSI-GE)

BACKGROUND

The Central Sensitization Inventory (CSI) is a screening tool designed to detect symptoms related to Central Sensitization (CS) and Central Sensitivity Syndromes (CSS) by measuring the degree of related phenomena. The objective of this study was to create a German, culturally-adapted version of the CSI and to test its psychometric properties.

METHODS

A German version of the CSI (CSI-GE) was developed, culturally-adapted, and pretested for comprehensibility. The psychometric properties of the resulting version were validated in a clinical study with chronic pain and pain-free control subjects. To assess retest reliability, the CSI-GE was administered twice to a subgroup of patients. Structural validity was tested using factor analyses. To investigate construct validity a hypotheses testing approach was used, including (1) correlations between the CSI-GE and several other well-established questionnaires as well as (2) an investigation of the CSI-GE discriminative power between different subgroups of participants believed to have different degrees of CS.

RESULTS

The CSI-GE showed excellent reliability, including high test-retest characteristics. Factor analyses confirmed a bi-factor dimensionality as has been determined previously. Analysing construct validity 6 out of 11 hypotheses (55%) were met. CSI-GE scores differentiated between subgroups according to expectations. Correlations between CSI-GE scores and other questionnaires suggested that none of the correlated constructs was identical, but there was overlap with other questionnaires based on symptom load. Several correlations did not fit with our current understanding of CS.

CONCLUSION

The CSI-GE appears to be a reliable tool for measuring CS/CSS-related symptomatology. Whether this implies that the CSI-GE measures the degree of CS within an individual subject remains unknown. The resulting score should be interpreted cautiously until further clarification of the construct.

G protein-coupled estrogen receptor in the rostral ventromedial medulla contributes to the chronification of postoperative pain

Aims

Chronification of postoperative pain is a common clinical phenomenon following surgical operation, and it perplexes a great number of patients. Estrogen and its membrane receptor (G protein‐coupled estrogen receptor, GPER) play a crucial role in pain regulation. Here, we explored the role of GPER in the rostral ventromedial medulla (RVM) during chronic postoperative pain and search for the possible mechanism.

Methods and Results

Postoperative pain was induced in mice or rats via a plantar incision surgery. Behavioral tests were conducted to detect both thermal and mechanical pain, showing a small part (16.2%) of mice developed into pain persisting state with consistent low pain threshold on 14 days after incision surgery compared with the pain recovery mice. Immunofluorescent staining assay revealed that the GPER‐positive neurons in the RVM were significantly activated in pain persisting rats. In addition, RT‐PCR and immunoblot analyses showed that the levels of GPER and phosphorylated μ‐type opioid receptor (p‐MOR) in the RVM of pain persisting mice were apparently increased on 14 days after incision surgery. Furthermore, chemogenetic activation of GPER‐positive neurons in the RVM of Gper‐Cre mice could reverse the pain threshold of pain recovery mice. Conversely, chemogenetic inhibition of GPER‐positive neurons in the RVM could prevent mice from being in the pain persistent state.

Conclusion

Our findings demonstrated that the GPER in the RVM was responsible for the chronification of postoperative pain and the downstream pathway might be involved in MOR phosphorylation.

Chronic Orofacial Pain: Models, Mechanisms, and Genetic and Related Environmental Influences

Chronic orofacial pain conditions can be particularly difficult to diagnose and treat because of their complexity and limited understanding of the mechanisms underlying their aetiology and pathogenesis. Furthermore, there is considerable variability between individuals in their susceptibility to risk factors predisposing them to the development and maintenance of chronic pain as well as in their expression of chronic pain features such as allodynia, hyperalgesia and extraterritorial sensory spread. The variability suggests that genetic as well as environmental factors may contribute to the development and maintenance of chronic orofacial pain. This article reviews these features of chronic orofacial pain, and outlines findings from studies in animal models of the behavioural characteristics and underlying mechanisms related to the development and maintenance of chronic orofacial pain and trigeminal neuropathic pain in particular. The review also considers the role of environmental and especially genetic factors in these models, focussing on findings of differences between animal strains in the features and underlying mechanisms of chronic pain. These findings are not only relevant to understanding underlying mechanisms and the variability between patients in the development, expression and maintenance of chronic orofacial pain, but also underscore the importance for considering the strain of the animal to model and explore chronic orofacial pain processes.

Pressure pain thresholds in individuals with knee pain: a cross-sectional study

Background

Knee osteoarthritis (KOA), chronic widespread pain (CWP) and overweight/obesity are public health problems that often coincide, and there is a multifactorial and unclear relationship between them. The study aimed to (1) investigate pain sensitivity, assessed by pressure pain thresholds (PPTs), among women and men with knee pain and (2) associations with, respectively, radiographic KOA (rKOA), CWP, and overweight/obesity.

Methods

Baseline data from an ongoing longitudinal study involving 280 individuals with knee pain in the 30–60 age group. Pain sensitivity was assessed by PPTs on eight different tender points using a pressure algometer. The participants’ knees were x-rayed. Self-reported CWP and number of pain sites were assessed with a pain figure, and overweight/obesity was measured using body mass index (BMI), visceral fat area (VFA), and body fat percentage, assessed with a bioimpedance. Associations were analysed using regression analyses.

Results

Women reported lower PPTs than men (p < 0.001), but no PPTs differences were found between those with and without rKOA. Low PPTs was associated with female sex, more pain sites, CWP, and a higher VFA and body fat percentage. The tender points second rib and the knees were most affected. The prevalence of CWP was 38 %.

Conclusions

The modifiable factors, increased VFA, and body fat could be associated with increased pain sensitivity among individuals with knee pain. Longitudinal studies are needed to further investigate the associations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04408-0.

Review of Literatures: Physiology of Orofacial Pain in Dentistry

The objective of this review of the literature is to summarize the physiology of orofacial pain in dentistry, particularly physiology of the pain pathway and molecular mechanisms on pathophysiology of pain, on account of new insights into classification of orofacial pain related diseases. This article will also focus on possible mechanisms of neuropathic orofacial pain which is distinguished from other types of pain.

Treatment responses in chronic temporomandibular patients depending on the treatment modalities and frequency of parafunctional behaviour

OBJECTIVES

(i) To evaluate the effect of three different interventions on treatment outcomes and (ii) to determine how the frequency of oral parafunction influences the effectiveness of the different therapeutic modalities.

METHODS

Forty-five participants were randomly assigned into three treatment groups [physical therapy (PT), stabilisation splint (SS) and control therapy (CT)]. According to Oral Behavior Checklist score, participants were divided into "high-frequency parafunction" (HFP) and low-frequency parafunction" (LFP) group. Primary (spontaneous pain and characteristic pain intensity) and secondary outcomes (range of mouth opening, anxiety symptoms, quality of life, perceived stress and global functional limitation) were evaluated during six-month treatment period.

RESULTS

Participants in PT group showed a significant reduction in characteristic pain intensity (p = .047, η²  = 0.243) when compared to SS and CT group, but significant improvement in spontaneous pain was found in all treatment groups. Patients treated with PT and SS exhibited significantly stronger improvement in pain-free mouth opening than patients in CT group (3rd month: p=.037, η2=0.258; 6th month: p = .005, η²  = 0.383). Within-group analyses showed significant decrease of perceived stress, anxiety symptoms and global functional limitation only in PT group over a six-month treatment period. Participants with HFP presented significantly greater levels of anxiety (3rd month: p = .009, η²  = 0.275; 6th month: p = .041, η²  = 0.176) than participants with LFP. Within-group analyses, however, showed significant improvement of anxiety, but also the decrease of perceived stress and improvement of global limitation for the HFP group but not for the LFP group.

CONCLUSION

Although no treatment can be marked as superior in terms of spontaneous pain relief, PT was more effective when observing relief of characteristic pain intensity. In HFP group the reduction of anxiety, stress and functional limitation was present regardless of the applied therapy.

TRIAL REGISTRATION

ClinicalTrials.gov NCT04694274. Registered on 01/04/2021.

Avoiding anchoring bias in unexplained chronic pain: an unexpected diagnosis of synovial osteochondromatosis

Unconscious biases may influence clinical decision making, leading to diagnostic error. Anchoring bias occurs when a physician relies too heavily on the initial data received. We present a 57-year-old man with a 3-year history of unexplained right thigh pain who was referred to a physiatry clinic for suggestions on managing presumed non-organic pain. The patient had previously been assessed by numerous specialists and had undergone several imaging investigations, with no identifiable cause for his pain. Physical examination was challenging and there were several 'yellow flags' on history. A thorough reconsideration of the possible diagnoses led to the discovery of hip synovial osteochondromatosis as the cause for his symptoms. Over-reliance on the referral information may have led to this diagnosis being missed. In patients with unexplained pain, it is important to be aware of anchoring bias in order to avoid missing rare diagnoses.

Reliability of Sonography Measures of the Lumbar Multifidus and Transversus Abdominis during Static and Dynamic Activities in Subjects with Non-Specific Chronic Low Back Pain

PURPOSE

The purpose of this study was to investigate the test-retest reliability of ultrasound (US) thickness measurements and the muscle contraction ratio (CR) of lumbar multifidus (LM) and transversus abdominis (TA) muscles in participants with and without nonspecific chronic low back pain (NCLBP).

METHODS

A total of 62 participants (37 with NCLBP, 25 without NCLBP) with participated in the study. The within-day and between-day reliability of US thickness measurements and CR in a lying (supine for TA and prone for LM) and sitting positions for both muscles (sitting on a gym ball with both feet on the ground or lifting one foot off the floor) were assessed. Reliability analysis was performed with intraclass correlations (ICCs) for these two static and dynamic positions.

RESULTS

Test-retest reliability was calculated to be good to high for the static position (ICC = 0.72-0.95) and the dynamic position (ICC = 0.74-0.94) sonographic measurements in both group of TA measurement. Test-retest reliability of LM measurements was good to high for the static position (ICC = 0.82-0.95) and the dynamic position (ICC = 0.85-0.97) sonographic measurements in both groups.

CONCLUSIONS

US imaging is a highly reliable method for the assessment of TA and LM thickness muscles in the dynamic position in participants with and without NCLBP. The CR measures may be adequately reliable in assessing the function of the TA and LM muscles in participants with NCLBP and healthy ones.

Pain Management in Clinical Practice Research Using Electronic Health Records

BACKGROUND

The use of electronic health record (EHR) systems encourages and facilitates the use of data for the development and surveillance of quality indicators, including pain management.

AIM

to conduct an integrative review on pain management research using data extracted from EHR in order to synthesize and analyze the following elements: pain management (assessments, interventions, and outcomes) and study results with potential clinical implications, data source, clinical sample characteristics, and method description.

DESIGN

An integrative review of the literature was undertaken to identify exemplars of scientific research studies that explore pain management using data from EHR, using Cooper's framework.

RESULTS

Our search of 1,061 records from PubMed, Scopus, and Cinahl was narrowed down to 28 eligible articles to be analyzed.

CONCLUSION

Results of this integrative review will make a critical contribution, assisting others in developing research proposals and sound research methods, as well as providing an overview of such studies over the past 10 years. Through this review it is therefore possible to guide new research on clinical pain management using EHR.

The role of regional anaesthesia and multimodal analgesia in the prevention of chronic postoperative pain: a narrative review

Effective prevention of chronic postoperative pain is an important clinical goal, informed by a growing body of studies. Peri-operative regional anaesthesia remains one of the most important tools in the multimodal analgesic toolbox, blocking injury-induced activation and sensitisation of both the peripheral and central nervous system. We review the definition and taxonomy of chronic postoperative pain, its mechanistic basis and the most recent evidence for the preventative potential of multimodal analgesia, with a special focus on regional anaesthesia. While regional anaesthesia targets several important aspects of the mechanistic pathway leading to chronic postoperative pain, evidence for its efficacy is still mixed, possibly owing to the heterogeneity of risk profiles within the surgical patient, but also to variation in techniques and medications reported in the literature.

Management of Procedural Pain in Children

In recent years, there has been increased interest in the study of pain in children and its treatment. It is known that when facing diagnostic and therapeutic procedures similar to those performed on adults, children either do not receive specific pain treatment or receive it on a significantly lower scale. However, recent research suggests a change in attitude and an improvement in the current treatment of children's pain. Although current knowledge demonstrates the falsity of many preconceived ideas about pain and its management, our results suggest that attitudinal change towards childhood pain remains slow and that real improvement in the training and practical application of the pediatrician who has to treat childhood pain is urgently needed. In this context, this manuscript has prepared standards and guidelines to improve pain management practices in a large number of national and international professional settings.

2020 AAHA Anesthesia and Monitoring Guidelines for Dogs and Cats

Risk for complications and even death is inherent to anesthesia. However, the use of guidelines, checklists, and training can decrease the risk of anesthesia-related adverse events. These tools should be used not only during the time the patient is unconscious but also before and after this phase. The framework for safe anesthesia delivered as a continuum of care from home to hospital and back to home is presented in these guidelines. The critical importance of client communication and staff training have been highlighted. The role of perioperative analgesia, anxiolytics, and proper handling of fractious/fearful/aggressive patients as components of anesthetic safety are stressed. Anesthesia equipment selection and care is detailed. The objective of these guidelines is to make the anesthesia period as safe as possible for dogs and cats while providing a practical framework for delivering anesthesia care. To meet this goal, tables, algorithms, figures, and "tip" boxes with critical information are included in the manuscript and an in-depth online resource center is available at aaha.org/anesthesia.

Perioperative Pregabalin for Preventive Analgesia in Breast Cancer Surgery: A Meta-analysis of Randomized Controlled Trials

OBJECTIVES

Pregabalin is a drug for neuropathic pain. Antipronociceptive properties of pregabalin have led to its recent use as an adjuvant to the multimodal postoperative pain regimen. This meta-analysis was conducted to evaluate the efficacy of perioperative pregabalin on acute and chronic postsurgical pain (CPSP) after breast cancer surgery.

METHODS

A meta-analysis including 8 randomized controlled trials searched from MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials was conducted. Subgroup analysis was performed according to doses and timecourse of pregabalin administration. Review Manager 5.3 was selected to conduct the meta-analysis.

RESULTS

Preoperative pregabalin in breast cancer surgery alleviated acute postoperative pain at rest 24 hours after surgery by 0.31 points on an 0 to 10 Numerical Rating Scale (95% confidence interval [CI] -0.57 to -0.05). Morphine consumption showed a decrease in postoperative use by 1.09 mg (95% CI: -1.61 to -0.57). The incidence of CPSP 3 months after surgery was reduced to 46% (95% CI: 0.25-0.85). Postoperative nausea and vomiting, dizziness, and sedation showed no overall significant reductions. However, a decrease in the incidence of postoperative nausea and vomiting and an increase in the incidence of dizziness were noted when patients received 300 mg of pregabalin before surgery.

DISCUSSION

This study demonstrated that pregabalin showed more efficacy on chronic pain than acute pain after a breast cancer surgery. Further study based on doses and treatment course of pregabalin should be conducted to establish stronger evidence of treatment effects.

Peripheral and central mechanisms of cough hypersensitivity

Chronic cough is a difficult to treat symptom of many respiratory and some non-respiratory diseases, indicating that varied pathologies can underpin the development of chronic cough. However, clinically and experimentally it has been useful to collate these different pathological processes into the single unifying concept of cough hypersensitivity. Cough hypersensitivity syndrome is reflected by troublesome cough often precipitated by levels of stimuli that ordinarily don't cause cough in healthy people, and this appears to be a hallmark feature in many patients with chronic cough. Accordingly, a strong argument has emerged that changes in the excitability and/or normal regulation of the peripheral and central neural circuits responsible for cough are instrumental in establishing cough hypersensitivity and for causing excessive cough in disease. In this review, we explore the current peripheral and central neural mechanisms that are believed to be involved in altered cough sensitivity and present possible links to the mechanism of action of novel therapies that are currently undergoing clinical trials for chronic cough.

Role of Nerve Growth Factor in Orofacial Pain

Some chronic pain conditions in the orofacial region are common and the mechanisms underlying orofacial pain are unresolved. Nerve growth factor (NGF) is a member of a family of neurotrophins and regulates the growth, maintenance and development of neurons. Increasing evidence suggests that NGF plays a crucial role in the generation of pain and hyperalgesia in different pain states. This review investigates the role of NGF in orofacial pain and their underlying cellular mechanisms, which may provide essential guidance to drug-discovery programmes. A systemic literature search was conducted in Pubmed focusing on NGF and orofacial pain. Articles were reviewed, and those discussing in vitro studies, animal evidence, clinical course, and possible mechanisms were summarized. We found a hyperalgesic effect of NGF in peripheral sensitization in orofacial pain models. We also summarize the current knowledge regarding NGF-dependent pain mechanism, which is initiated by retrograde transport of the ligand-receptor complex, ensuing transcriptional regulation of many important nociceptor genes involved in nociceptive processing. Phase III trials suggest that anti-NGF drug is endorsed with anti-inflammatory and pain-relieving effects with good tolerance in a variety of pain conditions, including pain associated with osteoarthritis and chronic lower back pain. Based on the data reviewed herein, NGF is believed to be an important hyperalgesic mediator in orofacial pain. The identification of underlying mechanisms and pathways of orofacial pain opens new frontiers for pain management.

Polygenic risk scores indicates genetic overlap between peripheral pain syndromes and chronic postsurgical pain

Chronic postsurgical pain (CPSP) is a debilitating chronic pain condition that has a substantial effect on quality of life. CPSP shows considerable clinical overlap with different chronic peripheral pain syndromes, suggesting a shared aetiology. This study aims to assess the genetic overlap between different chronic pain syndromes and CPSP, providing relevant biological context for potential chronic pain markers of CPSP. To analyse the genetic overlap between CPSP and chronic peripheral pain syndromes, recent GWAS studies were combined for polygenic risk scores (PRS) analysis, using a cohort of CPSP patients as starting point. Biological contextualisation of genetic marker, overlap between CPSP and chronic pain syndromes, was assessed through Gene Ontology (GO), using Pathway Scoring Algorithm (PASCAL) and REVIGO. PRS analyses suggest a significant genetic overlap between CPSP and 3 chronic pain disorders: chronic widespread pain (CWP, p value threshold = 0.003, R2 0.06, p = 0.003), rheumatoid arthritis (RA, p value threshold = 0.0177, R2 = 0.04, p = 0.017) and possibly sciatica (p value threshold = 0.00025, R2 = 0.03, p = 0.045). Whereas no significant genetic overlap was found with cluster headache and migraine, the outcome for osteoarthritis (OA) was inconsistent between the cohorts. This is likely related to cohort composition, as repeated random reallocation of patients' nullified CPSP/OA outcome variation between the discovery and replication cohorts. GO analyses suggested an aetiological involvement of genetic markers that control neurological signalling (specifically sodium channels) and inflammatory response. The current study reaffirms the impact of sample size, cohort composition and open data accessibility on the unbiased identification of genetic overlap across disorders. In conclusion, this study is the first to report genetic overlap between regulatory processes implicated in CPSP and chronic peripheral pain syndromes. Interaction between neurological signalling and inflammatory response may explain the genetic overlap between CPSP, CWP and RA. Enhanced understanding of mechanisms underlying chronification of pain will aid the development of new therapeutic strategies for CPSP with sodium channel biochemistry as a potential candidate.

The impact of fascia iliaca compartment block on chronic postsurgical pain in patients undergoing hip fracture repair

STUDY OBJECTIVE

Chronic postsurgical pain (CPSP), i.e. pain persisting >3 months, may appear after any type of surgery. There is a paucity of literature addressing CPSP development after hip fracture repair and the impact of any analgesic intervention on the development of CPSP in patients after hip fracture surgery. This study is the first aiming to examine the impact of ultrasound-guided fascia iliaca compartment block (USG FICB) on the development of CPSP after hip fracture repair.

DESIGN

Prospective randomized study.

SETTING

Operating room.

PATIENTS

182 patients scheduled for hip fracture surgery.

INTERVENTIONS

Patients were randomized to receive a USG FICB (FICB group) or a sham saline injection (sham FICB group), twenty minutes before positioning for spinal anesthesia.

MEASUREMENTS

The hip - related characteristic pain intensity (CPI) at 3- months post-surgery was the primary outcome measure. Presence and severity of hip-related pain at 3- and 6-months post-surgery, numeric rating pain scale (NRS) scores at 6, 24, 36, 48 postoperative hours, total 24-hour tramadol PCA administration and timing of the first tramadol dose, were documented as well.

MAIN RESULTS

FICB group presented with lower CPI scores 3- months postoperatively (p < 0.01), as well as lower percentage of patients with high-grade CPSP, 3 and 6 months postoperatively (p < 0.001). FICB group also showed significantly lower NRS scores in all instances, lower total 24 - hour tramadol consumption and higher mean time to first tramadol dose (p < 0.05). The overall sample of 182 patients reported a considerably high incidence of hip -related CPSP (60% at 3 months, 45% at 6 months).

CONCLUSIONS

USG FICB in the perioperative setting may reduce the incidence, intensity and severity of CPSP at 3 and 6 months after hip fracture surgery, providing safe and effective postoperative analgesia.

Predicting Factors of Pain Duration in Patients with Chronic Pain: A Large Population-based Study

Background

Chronic pain is the third main problem of global health and the most common cause of long-term disabilities. The duration that patients suffer from chronic pain is directly proportional to the extent of the suffering and to the amount of health care resources allocated to this problem. There is no research that has studied the risk factors associated with the long pain duration in chronic pain patients.

Methods

We investigated the potential risk factors associated with long pain duration in a population with diverse pain conditions in a cross-sectional study. We used a questionnaire that included a number of potential risk factors including sex, age, marital status, household condition, number of children, employment, education, body mass index (BMI), pain intensity, and the level of anxiety/depression. The data were analyzed by univariable and multivariable linear regression models.

Results

We recruited 780 patients. The analyses showed that age and abnormal BMI had a positive correlation with pain duration.

Conclusions

The risk factors that might be associated with longer pain duration include older age and abnormal BMI.

The Expanding Role of Ketamine in the Emergency Department

Patients frequently come to the emergency department for pain. For decades, ketamine has been used in the emergency department for procedural sedation but is now receiving attention as a potential alternative to opioids because of its unique analgesic effects. Additionally, ketamine's dissociative properties have made it a popular choice for sedating profoundly agitated patients. In this narrative review, these new roles for ketamine in the emergency department are discussed.

Salvia mellifera-How Does It Alleviate Chronic Pain?

Black sage, Salvia mellifera, can be made into a sun tea that is used as a foot soak to treat pain patients. The monoterpenoids and diterpenoids in the preparation penetrate the skin of the feet and stop the pain chemokine cycle, which may be the basis of chronic pain. Several chronic pain patients have reported long-term improvements in their pain after treatment with the preparation.

Associations of Elderly Onset Headache With Occurrence of Poor Functional Outcome, Cardiovascular Disease, and Cognitive Dysfunction During Long-term Follow-up

Background

Although the frequency and intensity of headaches decrease in older adults, headaches in this population are still an important neurological disorder. The purpose of this study was to investigate the associations of headache characteristics in older adults with the development of cardiovascular disease and cognitive dysfunction.

Methods

We prospectively enrolled 125 older (≥65 years old) patients with headache who were making their first visit to outpatient clinics and who had no prior history of cognitive dysfunction from 11 hospitals in Korea between August 2014 and February 2015. We investigated the occurrence of newly developed/or recurrent headache, cardiovascular disease, cognitive dysfunction, and poor functional outcomes.

Results

The mean age of all included patients was 72.6 years, 68.8% were women, and 43 (34.4%) had newly developed/or recurrent headache during follow-up. During a median follow-up of 31 months (interquartile range, 28–34 months), 21 participants (16.8%) experienced cardiovascular disease, and 26 (20.8%) developed cognitive dysfunction. Upon multivariate analysis and after adjusting for sex, age, and other factors, presence of newly developed/or recurrent headache was found to be associated with cardiovascular disease (hazard ratio [HR], 4.03; 95% confidence interval [CI], 1.28–12.61; p=0.017) and frequency of headache for the recent 3 months was related with cognitive dysfunction (HR, 1.05; 95% CI, 1.00–1.09; p=0.017) and poor functional outcomes (HR, 1.06; 95% CI, 1.01–1.11; p=0.011).

Conclusion

Our study demonstrated that there is an increased risk of cardiovascular disease, cognitive dysfunction, and poor functional outcomes in older patients with frequent, newly developed, or recurrent headache.

Nonanesthetic Effects of Ketamine: A Review Article

Ketamine is considered a dissociative anesthetic medication, and it is commonly administered by a parenteral route. It works mainly by blocking the N-methyl-D-aspartate receptor. It inhibits the voltage-gated Na and K channels and serotonin and dopamine reuptake; also, it affects specific receptors, such as α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, kainate, and aminobutyric acid A receptors. Ketamine appears to have particular mechanisms that are potentially involved during analgesic induction, including enhancing of descending inhibition and antiinflammatory effects. More recently, it has been shown that ketamine has potential in clinical practice for the management of chronic pain, cognitive function, depression, acute brain injury, and disorders of the immune system.