Mechanisms Challenges of the Pain Phenomenon

A 5000-year overview of the history of pain through ancient civilizations to modern pain theories

Pain and its management have been a predominant issue since the dawn of humanity. Pain has been the subject of much controversy and has constantly evolved across societies. The objective of this review is to trace the historical evolution of the concept of pain through the ages and to attempt to understand how modern theories of pain represent a legacy of ancestral knowledge passed down from culture to culture. We conducted a comprehensive review of primary and secondary sources across 6 major historical periods, including Pre-history, Antiquity, the Middle Ages, the Renaissance, the Modern, and Contemporary eras, using academic databases, specialized libraries, and historical archives. Results shows that during ancient civilizations, the understanding of pain oscillated between religious beliefs and medical advances. Antiquity societies made significant contributions to the understanding of pain mechanisms and management. Contrary to popular belief, significant advances were made during the Middle Ages despite the important impact of religion on the era's conceptualization of pain. During the Renaissance, the influence of religion waned, and secular medicine made significant progress. The development of pain theories peaked in the 19th century with technological advances. Long considered an expression of internal suffering, pain has fascinated humanity throughout history. The way pain has been perceived, understood, and treated has changed greatly over the centuries. This historical scientific review allows us to keep in mind that the vision we have of pain in Western society is predominantly based on the concrete heritage of ancient civilizations.

Monitoring Chronic Non-Cancer Pain in Denmark Over Two Decades: Prevalence, Mental Health and Loneliness

BACKGROUND

Epidemiological surveys have monitored chronic non-cancer pain (CNCP) and investigated associated factors in Denmark for more than 20 years. This study aimed to analyse CNCP prevalence in the Danish population from 2000 to 2023 and its associations with mental health status and loneliness.

METHODS

Population-based surveys were conducted between 2000 and 2023. In all waves, residents aged ≥ 16 years were randomly selected to complete a self-administered questionnaire. Samples included 10,089 respondents in 2000, 5292 in 2005, 14,330 in 2010, 13,429 in 2013, 13,050 in 2017, 10,384 in 2021 and 9303 in 2023. CNCP was defined as pain lasting ≥ 6 months. Mental status was assessed by Mental Component Summary score of Short Form-12 and severe loneliness by the Three-Item Loneliness Scale. Calibration weighting was applied to reduce potential non-response bias.

RESULTS

The prevalence of CNCP increased steadily by 9.4 percentage points from 2000 (19.5%) to 2023 (28.9%), but with a downward tick during the COVID-19 pandemic in 2021 (25.3%). Women aged 45 years or older had the highest prevalence in all waves. Results showed a worsening of mental health over time in both individuals with and without CNCP; however, the lowest scores were reported by individuals with CNCP. Severe loneliness seemed to be a substantial problem in individuals with CNCP (17.3% in 2021).

CONCLUSIONS

In summary, CNCP was highly prevalent over the given period and associated with mental health status and severe loneliness in recent years.

SIGNIFICANCE

This study demonstrated alarming trend on chronic non-cancer pain prevalence over time in Denmark. The high estimates of prevalence and related issues, such as mental health and severe loneliness deserve further investigation and prioritisation in the public health agenda.

Patient Fear of Pain: The Pre-Operative Period in the Neurosurgery Clinic

PURPOSE

This study was conducted as a descriptive study to determine the pain fears of patients undergoing surgery in the neurosurgery clinic.

MATERIAL AND METHOD

The study was conducted with 151 patients hospitalized in the neurosurgery clinic who met the inclusion criteria. Data were collected with the patient information form and the fear of pain scale-III. Ethics committee approval, institutional permission, and written consent from individuals were obtained before the study.

RESULTS

It was determined that the mean fear of pain score was 64.59 ± 18.43, 41.7% of the patient were fear of surgical incisional pain. Fear of surgical incisional pain is responsible for 22.0% and female gender is responsible for 29% of the change in fear of pain scores.

CONCLUSION

As a result, it was determined that the pain fear level of the patients in the pre-operative period was moderate. Increasing the practices to reduce the patients' fear of pain should be recommended.

The effect of prolonged elbow pain and rTMS on cortical inhibition: A TMS-EEG study

Introduction

Recent studies using combined transcranial magnetic stimulation (TMS) and electroencephalography (EEG) have shown that pain leads to an increase in the N45 peak of the TMS-evoked potential (TEP), which is mediated by GABAergic inhibition. Conversely, 10Hz repetitive TMS (10Hz-rTMS), which provides pain relief, reduces the N45 peak. However, these studies used brief pain stimuli (lasting minutes), limiting their clinical relevance. The present study determined the effect of pain and 10Hz-rTMS on the N45 peak in a prolonged pain model (lasting several days) induced by nerve growth factor (NGF) injection to the elbow muscle.

Materials and Methods

Experiment 1 : TEPs were measured in 22 healthy participants on Day 0 (pre-NGF), Day 2 (peak pain), and Day 7 (pain resolution). Experiment 2 : We examined the effect of 5 days of active (n=16) or sham (n=16) rTMS to the left primary motor cortex (M1) on the N45 peak during prolonged NGF-induced pain, with TEPs measured on Day 0 and Day 4 (post-rTMS).

Results

Experiment 1: While no overall change in the N45 peak was seen, a correlation emerged between higher pain severity on Day 2 and a larger increase in the N45 peak. Experiment 2 : Active rTMS reduced the N45 peak on Day 4 vs. Day 0, with no effect in the sham group.

Conclusion

Our findings suggest that (i) higher pain severity correlates with an increase in the N45 peak, and (ii) rTMS decreases cortical inhibition in a model of prolonged experimental pain. This study extends previous research by demonstrating a link between pain perception and cortical inhibition within a prolonged pain context.

Criteria and Guidelines for Returning to Running Following a Tibial Bone Stress Injury: A Scoping Review

Tibial bone stress injuries (BSIs) are common among long-distance runners. They have a high recurrence rate, and complexity emerges in the wider management and successful return to running. Following a tibial BSI, a critical component of complete rehabilitation is the successful return to running, and there is a lack of consistency or strong evidence to guide this process. The objectives of this review were to outline the criteria used in clinical decision-making prior to resuming running, and to establish evidence-based guidelines for the return to running process following a tibial BSI. Electronic databases including MEDLINE, CINAHL, Scopus, SPORTDiscus and AMED were searched for studies that stated criteria or provided guidelines on the objectives above. Fifty studies met the inclusion criteria and were included. Thirty-nine were reviews or clinical commentaries, three were retrospective cohort studies, two were randomised controlled trials, two were pilot studies, one was a prospective observational study, and three were case studies. Therefore, the recommendations that have been surmised are based on level IV evidence. Decisions on when an athlete should return to running should be shared between clinicians, coaches and the athlete. There are five important components to address prior to introducing running, which are: the resolution of bony tenderness, pain-free walking, evidence of radiological healing in high-risk BSIs, strength, functional and loading tests, and the identification of contributing factors. Effective return to running planning should address the athlete's risk profile and manage the risk by balancing the athlete's interests and reinjury prevention. An individualised graduated return to running programme should be initiated, often starting with walk-run intervals, progressing running distance ahead of speed and intensity, with symptom provocation a key consideration. Contributing factors to the initial injury should be addressed throughout the return to run process.

Conditioned pain modulation, kinesiophobia, and pain catastrophizing as prognostic factors for chronicity in a population with acute low back pain: An exploratory prospective study

BACKGROUND

Psychosocial factors and alteration of the somatosensory functions have been associated with persistent low back pain (LBP). A decreased capacity of the central nervous system to modulate pain has been suggested as a potential contributor to the persistence of pain.

OBJECTIVE

To investigate whether conditioned pain modulation (CPM), initial symptoms/disability, kinesiophobia, and pain catastrophizing is associated with the transition from acute to chronic LBP.

DESIGN

Prospective cohort study.

METHOD

Fifty participants presenting with acute LBP (<6 weeks) took part in three evaluation sessions (baseline, 3 and 6 months). At baseline and 3-month evaluations, all participants completed self-administered questionnaires (Oswestry Disability Index [ODI], Short Form of Brief Pain Inventory [BPI-SF], Tampa Scale of Kinesiophobia [TSK] and Pain Catastrophizing Scale [PCS]) and CPM was assessed. At the 6-month evaluation, questionnaires were readministered, and participants were dichotomized according to their status (Non-chronic LBP [NCLBP] or chronic LBP [CLBP]). Univariate tests were used to compare baseline variables between NCLBP and CLBP.

RESULTS

No significant baseline difference was found for TSK (p = 0.48), PCS (p = 0.78), CPM (p = 0.82), ODI (p = 0.78), BPI-SF severity (p = 0.50), and interference subscales (p = 0.54) between those categorized as NCLBP or CLBP at 6 months.

CONCLUSIONS

This exploratory study failed to support the hypothesis that inefficient CPM mechanisms and the presence of psychological factors could be factors associated with the transition to chronic pain in individuals with acute LBP.

Summarizing the effects of different exercise types in chronic neck pain - a systematic review and meta-analysis of systematic reviews

BACKGROUND

To date, no consensus exists as to whether one exercise type is more effective than another in chronic neck pain. This systematic review and meta-analysis of systematic reviews aimed to summarize the literature on the effect of various exercise types used in chronic neck pain and to assess the certainty of the evidence.

METHODS

We searched the databases Ovid MEDLINE, Embase, Cochrane Library, SportDiscus, and Web of Science (Core Collection) for systematic reviews and meta-analyses on adults between 18 and 70 years with chronic neck pain lasting ≥ 12 weeks which investigated the effects of exercises on pain and disability. The included reviews were grouped into motor control exercise (MCE), Pilates exercises, resistance training, traditional Chinese exercise (TCE), and yoga. Study quality was assessed with AMSTAR-2 and the level of certainty for the effects of the exercise through GRADE. A narrative analysis of the results was performed and in addition, meta-analyses when feasible.

RESULTS

Our database search resulted in 1,794 systematic reviews. We included 25 systematic reviews and meta-analyses including 17,321 participants (overlap not accounted for). The quality of the included reviews ranged from critically low to low (n = 13) to moderate to high (n = 12). We found low to high certainty of evidence that MCE, Pilates exercises, resistance training, TCE, and yoga have short-term positive effects on pain and that all exercise types except resistance training, show positive effects on disability compared to non-exercise controls. We found low to moderate certainty of evidence for conflicting results on pain and disability when the exercise types were compared to other exercise interventions in the short-term as well as in intermediate/long-term apart for yoga, as no long-term results were available.

CONCLUSION

Overall, our findings show low to high certainty of evidence for positive effects on pain and disability of the various exercise types used in chronic neck pain compared to non-exercise interventions, at least in the short-term. Based on our results, no optimal exercise intervention for patients with chronic neck pain can be recommended, since no large differences between the exercise types were shown here. Because the quality of the included systematic reviews varied greatly, future systematic reviews need to increase their methodological quality.

TRIAL REGISTRATION

Prospero CRD42022336014.

Multifaceted Roles of ALK Family Receptors and Augmentor Ligands in Health and Disease: A Comprehensive Review

This review commemorates the 10-year anniversary of the discovery of physiological ligands Augα (Augmentor α; ALKAL2; Fam150b) and Augβ (Augmentor β; ALKAL1; Fam150a) for anaplastic lymphoma kinase (ALK) and leukocyte tyrosine kinase (LTK), previously considered orphan receptors. This manuscript provides an in-depth review of the biophysical and cellular properties of ALK family receptors and their roles in cancer, metabolism, pain, ophthalmology, pigmentation, central nervous system (CNS) function, and reproduction. ALK and LTK receptors are implicated in the development of numerous cancers, and targeted inhibition of their signaling pathways can offer therapeutic benefits. Additionally, ALK family receptors are involved in regulating body weight and metabolism, modulating pain signaling, and contributing to eye development and pigmentation. In the CNS, these receptors play a role in synapse modulation, neurogenesis, and various psychiatric pathologies. Lastly, ALK expression is linked to reproductive functions, with potential implications for patients undergoing ALK inhibitor therapy. Further research is needed to better understand the complex interactions of ALK family receptors and Aug ligands and to repurpose targeted therapy for a wide range of human diseases.

High- Versus Low-Dose Exercise Therapy for Knee Osteoarthritis : A Randomized Controlled Multicenter Trial

BACKGROUND

The benefits of exercise in patients with knee osteoarthritis are well documented, but the optimal exercise dose remains unknown.

OBJECTIVE

To compare high-dose versus low-dose exercise therapy with regard to knee function, pain, and quality of life (QoL) in patients with long-term symptomatic knee osteoarthritis.

DESIGN

A Swedish and Norwegian multicenter randomized controlled superiority trial with multiple follow-ups up to 12 months after the intervention. (ClinicalTrials.gov: NCT02024126).

SETTING

Primary health care facilities.

PATIENTS

189 patients with diagnosed knee osteoarthritis and a history of pain and decreased knee function were assigned to high-dose therapy (n = 98; 11 exercises; 70 to 90 minutes) or low-dose therapy (n = 91; 5 exercises; 20 to 30 minutes).

INTERVENTION

Patient-tailored exercise programs according to the principles of medical exercise therapy. Global (aerobic), semiglobal (multisegmental), and local (joint-specific) exercises were performed 3 times a week for 12 weeks under supervision of a physiotherapist.

MEASUREMENTS

The Knee Injury and Osteoarthritis Outcome Score (KOOS) was measured biweekly during the 3-month intervention period and at 6 and 12 months after the intervention. The primary end point was the mean difference in KOOS scores between groups at the end of the intervention (3 months). Secondary outcomes included pain intensity and QoL. The proportion of patients with minimal clinically important changes in primary and secondary outcomes was compared between groups.

RESULTS

Both groups improved over time, but there were no benefits of high-dose therapy in most comparisons. One exception was the KOOS score for function in sports and recreation, where high-dose therapy was superior at the end of treatment and at 6-month follow-up. A small benefit in QoL at 6 and 12 months was also observed.

LIMITATION

There was no control group that did not exercise.

CONCLUSION

The results do not support the superiority of high-dose exercise over low-dose exercise for most outcomes. However, small benefits with high-dose exercise were found for knee function in sports and recreation and for QoL.

PRIMARY FUNDING SOURCE

Swedish Rheumatic Fund.

Pain Science in Practice (Part 4): Central Sensitization I

SYNOPSIS: Central sensitization is an umbrella term for facilitated synaptic plasticity. This editorial (1) explains the differences between homosynaptic and heterosynaptic plasticity, (2) explains the role of glia cells in dorsal horn neuroplasticity, and (3) briefly discusses the clinical relevance of central sensitization and nociplastic pain. Part 5 covers wind-up, classical central sensitization, and long-term potentiation. J Orthop Sports Phys Ther 2023;53(1):1-4. doi:10.2519/jospt.2023.11569.

Television-viewing time and bodily pain in Australian adults with and without type 2 diabetes: 12-year prospective relationships

BACKGROUND

Bodily pain is a common presentation in several chronic diseases, yet the influence of sedentary behaviour, common in ageing adults, is unclear. Television-viewing (TV) time is a ubiquitous leisure-time sedentary behaviour, with a potential contribution to the development of bodily pain. We examined bodily pain trajectories and the longitudinal relationships of TV time with the bodily pain severity; and further, the potential moderation of the relationships by type 2 diabetes (T2D) status.

METHOD

Data were from 4099 participants (aged 35 to 65 years at baseline) in the Australian Diabetes, Obesity and Lifestyle Study (AusDiab), who took part in the follow-ups at 5 years, 12 years, or both. Bodily pain (from SF36 questionnaire: a 0 to 100 scale, where lower scores indicate more-severe pain), TV time, and T2D status [normal glucose metabolism (NGM), prediabetes, and T2D] were assessed at all three time points. Multilevel growth curve modelling used age (centred at 50 years) as the time metric, adjusting for potential confounders, including physical activity and waist circumference.

RESULTS

Mean TV time increased, and bodily pain worsened (i.e., mean bodily pain score decreased) across the three time points. Those with T2D had higher TV time and more-severe bodily pain than those without T2D at all time points. In a fully adjusted model, the mean bodily pain score for those aged 50 years at baseline was 76.9(SE: 2.2) and worsened (i.e., bodily pain score decreased) significantly by 0.3(SE: 0.03) units every additional year (p <0.001). Those with initially more-severe pain had a higher rate of increase in pain severity. At any given time point, a one-hour increase in daily TV time was significantly associated with an increase in pain severity [bodily pain score decreased by 0.69 (SE: 0.17) units each additional hour; p <0.001], accounting for the growth factor (age) and confounders' effects. The association was more-pronounced in those with T2D than in those without (prediabetes or NGM), with the effect of T2D on bodily pain severity becoming more apparent as TV time increases, significantly so when TV time increased above 2.5 hours per day.

CONCLUSION

Bodily pain severity increased with age in middle-aged and older Australian adults over a 12-year period, and increments in TV time predicted increased bodily pain severity at any given period, which was more pronounced in those with T2D. While increasing physical activity is a mainstay of the prevention and management of chronic health problems, these new findings highlight the potential of reducing sedentary behaviours in this context.

Whole-Body Cryostimulation in Fibromyalgia: A Scoping Review

Currently, all available therapies for the control and management of fibromyalgia (FM) are mostly focused on relieving patients’ symptoms and improving their quality of life. The purpose of this review is to provide an up-to-date overview of the evidence supporting the beneficial effects of whole-body cryostimulation (WBC) in patients with FM and evidence-based guidance on the possible adjuvant use of WBC in the treatment of FM. We searched the most recent literature by retrieving 10 eligible studies, 4 of which were abstracts only, from a total of 263 records. Thermal stress caused by cryostimulation induces an analgesic effect, improving pain, redox balance, and inflammatory symptoms in an exercise-mimicking fashion. In addition, it reduces the feeling of fatigue, improves mood, and reduces mental health deterioration with positive consequences on depressive states and improved sleep quality. Although the studies included in this review are not of sufficient quality and quantity to draw definitive conclusions about the effectiveness of WBC in FM, initial evidence indicates WBC as a promising add-on option in the multidisciplinary treatment of FM, due to its rapid action and high patients’ compliance. The application of WBC protocols has the potential to expand therapeutic options for the treatment of FM and related disorders; however, larger, high-quality primary studies are still needed.