Insights into the mechanisms and the emergence of sex-differences in pain

Deciphering nociplastic pain: clinical features, risk factors and potential mechanisms

Nociplastic pain is a mechanistic term used to describe pain that arises or is sustained by altered nociception, despite the absence of tissue damage. Although nociplastic pain has distinct pathophysiology from nociceptive and neuropathic pain, these pain mechanisms often coincide within individuals, which contributes to the intractability of chronic pain. Key symptoms of nociplastic pain include pain in multiple body regions, fatigue, sleep disturbances, cognitive dysfunction, depression and anxiety. Individuals with nociplastic pain are often diffusely tender - indicative of hyperalgesia and/or allodynia - and are often more sensitive than others to non-painful sensory stimuli such as lights, odours and noises. This Review summarizes the risk factors, clinical presentation and treatment of nociplastic pain, and describes how alterations in brain function and structure, immune processing and peripheral factors might contribute to the nociplastic pain phenotype. This article concludes with a discussion of two proposed subtypes of nociplastic pain that reflect distinct neurobiological features and treatment responsivity.

Association Between Self-Construals, Social Pain Sensitivity, and Gender in Young Adults

We experience pain in response to negative, unwanted social interaction with others (e.g., social rejection), and this type of pain is termed as social pain in the recent literature. While sensitivity to social pain may be beneficial to increase a chance for survival, social pain sensitivity could also be detrimental to elevate the risk of various health issues. Such opposing natures of social pain sensitivity warrants research to better identify factors that are linked to social pain sensitivity. Self-construals show perspectives on how to view oneself in relations to others, characterized as independent and interdependent self-construals, and may be linked to social pain sensitivity. Additionally, pervious data have indicated gender differences in social pain sensitivity, but it is unclear if self-construals explain gender differences in social pain sensitivity. Therefore, this study examined if self-construals were associated with social pain sensitivity, and gender differences in social pain sensitivity were accounted for by self-construals. The participants were 148 college students who completed several self-report questionnaires to evaluate self-construals and social pain sensitivity. The results indicated that interdependent tendency, which showed higher interdependent self-construal than independent self-construal, was associated with social pain sensitivity. While gender differences in social pain sensitivity were confirmed, gender differences in social pain sensitivity were not accounted for by interdependent tendency. The results suggest that interdependent tendency is associated with social pain sensitivity, but is not involved in gender differences in social pain sensitivity.

The epidemiology of neck and low back pain in Iran: a national and sub-national analysis from 1990 to 2019

Background

Neck pain (NP) is a condition influenced by multiple factors. It places a significant burden on individuals suffering from NP and on social and economic systems. On a global scale, low back pain (LBP) stands out as a significant contributor to years lost to disability, and this burden is on the rise due to population growth and aging.

Methods

The Global Burden of Disease database was used to collect data on the prevalence, incidence, and years lived with disability (YLD) of NP and LBP between 1990 and 2019. Various factors, including age group, gender, Iran, and its 31 provinces, were used to classify the data.

Results

Iran accounted for 0.86 million incident cases of NP in 2019, with age-standardized incident rate per 100 000 population of 934.1. Tehran has the maximum age-standardized prevalence, incidence, and YLD. Iran accounted for the age-standardized incidence rate for LBP per 100 000 population of 3492.9, and it reduced to -8.35% from 1990. Mazandaran exhibits the highest levels of prevalence, incidence, and YLD for LBP in 2019. In Iran, the point prevalence of NP in 2019 was higher in females and increased with age up to 50-54 years for females and 70-74 years for males. However, there is only a slight difference between females and males in Iran regarding LBP prevalence.

Conclusions

In this study, the authors report the prevalence, incidence, YLD, and age-standardized rates for NP and LBP in the world's general population and Iran's population based on its sub-nations in 1990 and 2019.

Analgesia Administration by Sex Among Pediatric Emergency Department Patients with Abdominal Pain

Background

There is conflicting data about sex-based differences in the treatment of acute pain in the ED. Little is known about sex-based disparities in analgesia in pediatric ED patients.

Objectives

Our objective was to determine whether analgesic administration rates differ between female and male pediatric patients presenting to the ED with abdominal pain.

Methods

We conducted a retrospective cohort study of ED patients 5-21 years old with abdominal pain between 6/1/19 and 6/30/21. The primary outcome was receipt of any analgesia, and secondary outcomes were receipt of opioid analgesia and time to receipt of analgesia. Multivariable regression models were fitted for each outcome.

Results

We studied 1,087 patients; 681 (63%) were female with a median age of 17 years (IQR 13, 19) and 406 (37%) were male with a median age of 14 years (IQR 9, 18). 371 female patients (55%) and 180 male patients (44%) received any analgesia. 132 female patients (19%) and 83 male patients (20%) received opioid analgesia. In multivariate analyses, female patients were equally likely to receive any analgesia (OR 1.30, 95% CI 0.97 - 1.74, p = 0.07), but time to analgesia was 14% longer (GMR 1.14, 95% CI 1.00 - 1.29, p = 0.04). Non-White patients were 32% less likely to receive opioids (OR 0.68, 95% CI 0.47 - 0.97, p = 0.04).

Conclusions

Female pediatric ED patients were equally likely to receive any analgesia as male patients, but their time to analgesia was longer. Non-White patients were less likely to receive opioid analgesia than White patients.

The relationship between chronic diseases and the intensity and duration of low back pain

BACKGROUND

Low back pain (LBP) is a worldwide problem that affects numerous people and limits their mobility. Several factors, including chronic diseases, increase the risk of developing LBP. To date, the information available about the relationship between chronic diseases and the intensity and duration of LBP is quite limited.

AIM

The aim of the present study was to address the relationship between chronic diseases and both the intensity and duration of LBP.

DESIGN

This is an observational cross-sectional study.

SETTING

The study was conducted in the community of Saudi Arabia.

POPULATION

2181 adult participants (aged 18 years or more, mean age of 33 and standard deviation [SD] of ±11, 61% females) from Saudi Arabia with either recent or recurring LBP participated in the study.

METHODS

The participants of this study were surveyed, and their demographic information was obtained. They were asked whether they had LBP during the past year, and if they had, they were asked about their LBP in terms of the pain intensity on a scale that runs from 0 to 10, where 0 indicates no pain and 10 indicates extreme pain. Further, the participants were asked how long their pain lasted (in days). They were also inquired whether they had any of the following chronic diseases: diabetes mellitus, high blood pressure, hypotension, arthritis, cardiopulmonary diseases, kidney diseases, and hypothyroidism. Logistic regression was used to analyze the relationships between both of LBP's intensity and duration, and the presence of chronic diseases, while adjusting for the potential effect of age and gender.

RESULTS

A total of 2181 adults with either new onset of or recurrent LBP during the past 12 months participated in the present study. Of these, 356 (16%), who had LBP, suffered from one or more of the said chronic diseases. It was found that having one or more chronic diseases had statistically significant relationship with increased LBP's intensity (P=0.002), as well as prolonged duration (P=0.001). In particular, hypertension, arthritis, and hypothyroidism have statistically significant relationship with increased the intensity of the pain (P<0.05). Only, hypertension and arthritis have statistically significant relationship with increased the duration of pain (P≤0.001).

CONCLUSIONS

The presence of chronic diseases was associated with a more intense and longer duration of LBP.

CLINICAL REHABILITATION IMPACT

In view of the results of this study, we expect that those who have chronic diseases will have a longer duration of LBP and more intense pain.

Effectiveness of Self-Care Education for Chronic Neck Pain: A Systematic Review and Meta-Analysis

Self-care programs for chronic neck pain are relevant to everyday life and can lead to long- term improvement. More studies on their effectiveness, key components and appropriate duration are needed. The aim of this study was to determine the effectiveness of self-care programs for patients with chronic neck pain. A systematic review and meta-analysis of randomized controlled trials was conducted according to the PRISMA guidelines. After searching in PubMed, Web of Science, Scopus and ScienceDirect, eleven studies met the inclusion criteria. Self-care education interventions typically consisted of education (i.e., pain neuro-science education or general educational concepts) accompanied by exercise or manual therapy. The most frequent components were addressing physical and psychological symptoms and engaging in self-care strategies. The least frequent ones were monitoring and recording symptoms and discussing with providers of medical care. The duration of the interventions ranged from three sessions to six months. Finally, individual and supervised modalities were the most frequent. After pooling the data, a meta-analysis was carried out according to four variables (i.e., pain, disability, kinesiophobia and catastrophization) and showed significant results (p < 0.05) in favor of self-care interventions. This systematic review and meta-analysis suggests that self-education interventions improve pain, psychological pain-related variables and disability in patients with chronic neck pain. The most frequently used components were addressing physical and psychological symptoms and engaging in self-care strategies. Future trials should focus on including other components, such as discussing symptoms with providers of medical care or self-monitoring symptoms. Additional areas of focus include more homogeneous doses and comparator treatments, as well as studies with better evidence to reach more solid conclusions.

Relating Spinal Injury-Induced Neuropathic Pain and Spontaneous Afferent Activity to Sleep and Respiratory Dysfunction

Abstract Spinal cord injury (SCI) can induce dysfunction in a multitude of neural circuits including those that lead to impaired sleep, respiratory dysfunction, and neuropathic pain. We used a lower thoracic rodent contusion SCI model of neuropathic pain that has been shown to associate with increased spontaneous activity in primary afferents and hindlimb mechanosensory stimulus hypersensitivity. Here we paired capture of these variables with chronic capture of three state sleep and respiration to more broadly understand SCI-induced physiological dysfunction and to assess possible interrelations. Noncontact electric field sensors were embedded into home cages to non-invasively capture the temporal evolution of sleep and respiration changes for six weeks after SCI in naturally behaving mice. Hindlimb mechanosensitivity was assessed weekly, and terminal experiments measured primary afferent spontaneous activity in situ from intact lumbar dorsal root ganglia (DRG). We observed that SCI led to increased spontaneous primary afferent activity (both firing rate and the number of spontaneously active DRGs) that correlated with increased respiratory rate variability and measures of sleep fragmentation. This is the first study to measure and link sleep dysfunction and variability in respiratory rate in a SCI model of neuropathic pain, and thereby provide broader insight into the magnitude of overall stress burden initiated by neural circuit dysfunction after SCI.

Sex Differences in Pain and Quantitative Sensory Testing in Patients With Rheumatoid Arthritis

OBJECTIVE

Women with rheumatoid arthritis (RA) have higher pain and worse functional outcomes compared to men, even when treated with similar medications. The objective of this study was to identify sex differences in pain intensity, pain interference, and quantitative sensory tests (QST), which are independent of inflammation, in patients with RA.

METHODS

This study is a post hoc analysis of participants in the Central Pain in Rheumatoid Arthritis cohort. Pain intensity was assessed using a 0-10 numeric rating scale. Pain interference was measured using a Patient-Reported Outcomes Measurement Information System computerized adaptive test. QST included pressure pain detection thresholds, temporal summation, and conditioned pain modulation. Women and men were compared using multiple linear regression, adjusted for age, education, race, research site, depression, obesity, RA disease duration, swollen joint count, and C-reactive protein.

RESULTS

Mean ± SD pain intensity was 5.32 ± 2.29 among women with RA, compared to 4.60 ± 2.23 among men with RA (adjusted difference 0.83 [95% confidence interval (95% CI) 0.14, 1.53]). Women with RA had lower pressure pain detection thresholds at the trapezius (adjusted difference -1.22 [95% CI -1.73, -0.72]), wrist (adjusted difference -0.57 [95% CI -1.07, -0.06]), and knee (adjusted difference -1.10 [95% CI -2.00, -0.21]). No statistically significant differences in pain interference, temporal summation, and conditioned pain modulation were observed.

CONCLUSION

Women reported higher pain intensity and lower pressure pain detection thresholds (higher pain sensitivity) than men. However, pain interference, temporal summation, and conditioned pain modulation did not differ between men and women.

The burden of neck pain in the Middle East and North Africa region, 1990-2019

Background

Neck pain is a common cause of disability across the world. The objective of the present study was to present a thorough investigation of the burden caused by neck pain in the Middle East and North Africa (MENA) region, by country, sex, age group and socio-demographic index (SDI).

Methods

The data on the burden of neck pain, encompassing its prevalence, incidence and years lived with disability (YLDs), were extracted from the Global Burden of Disease (GBD) 2019 study. These findings are reported as age-standardised numbers and rates (per 100,000), accompanied by 95 % uncertainty intervals (UIs).

Results

The age-standardised point prevalence of neck pain in 2019 was 3066.7 (95 % UI: 2407.8 to 3894.3) per 100,000, with an age-standardised incidence rate of 649.2 (509.2-829.2) in the MENA region, neither of which have changed since 1990. The age-standardised YLD rate of neck pain was 303.0 (201.5-438.8) per 100,000 population in 2019. The highest YLD rate of neck pain was found in Iran [423.5 (280.3-609.8)] and the lowest in Kuwait [215.0 (141.0-314.1)]. The highest number of prevalent cases were seen in the 45-49 age-group for both sexes in 2019, but overall females had a higher point prevalence than males. Furthermore, over the study period (1990-2019) there was no clear and consistent relationship between the SDI and the burden of neck pain.

Conclusion

Although the burden of neck pain has largely remained stable over the past three decades, the prevalence and morbidity in the MENA region remains high. Preventive and rehabilitative programs should be implemented that firstly target middle-aged females and males.

Physiological response to pain in female adolescents with nonsuicidal self-injury as a function of severity

BACKGROUND

Preliminary evidence indicates altered hypothalamic-pituitary-adrenal (HPA) axis and autonomic nervous system (ANS) response to experimental pain in individuals with nonsuicidal self-injury (NSSI). This study investigated effects of NSSI severity and severity of psychopathology on the HPA axis and ANS response to pain.

METHODS

N = 164 adolescents with NSSI and n = 45 healthy controls received heat pain stimulation. Salivary cortisol, α-amylase and blood pressure were repeatedly assessed before and after painful stimulation. Heart rate (HR) and heart rate variability (HRV) were assessed continuously. NSSI severity and comorbid psychopathology were derived from diagnostic assessments. Main and interaction effects of time of measurement and NSSI severity, adjusted for severity of adverse childhood experiences, borderline personality disorder and depression, on HPA axis and ANS response to pain were examined using regression analyses.

RESULTS

Increasing NSSI severity predicted an increasing cortisol response (χ2(3) = 12.09, p = .007) to pain. After adjusting for comorbid psychopathology, greater NSSI severity predicted decreased α-amylase levels following pain (χ2(3) = 10.47, p = .015), and decreased HR (χ2(2) = 8.53, p = .014) and increased HRV(χ2(2) = 13.43, p = .001) response to pain.

LIMITATIONS

Future research should implement several NSSI severity indicators, potentially revealing complex associations with the physiological response to pain. Assessing physiological responses to pain in NSSI in a naturalistic setting presents a promising avenue for future research in NSI.

CONCLUSIONS

Findings indicate an increased pain-related HPA axis response and an ANS response characterized by reduced sympathetic and increased parasympathetic activity associated with NSSI severity. Results support claims for dimensional approaches to NSSI and its related psychopathology alongside shared, underlying neurobiological correlates.

Precision management of post-COVID pain: An evidence and clinical-based approach

Background Pain after a SARS-CoV-2 acute infection (post-COVID pain) is becoming a new healthcare emergency but remains underestimated and most likely undertreated due to a lack of recognition of the phenomenon and knowledge of the underlying pain mechanisms. Evidence supporting any particular treatment approach for the management of post-COVID pain is lacking. Large variability in the patient response to any standard pain treatments is clinically observed, which has led to calls for a personalized, tailored approach to treating patients with chronic post-COVID pain (i.e. 'precision pain medicine'). Applying the global concerted action towards precision medicine to post-COVID pain could help guide clinical decision-making and aid in more effective treatments. Methods The current position paper discusses factors to be considered by clinicians for managing post-COVID pain ranging from identification of the pain phenotype to genetic consideration. Results The ability of clinicians to phenotype post-COVID pain into nociceptive, neuropathic, nociplastic or mixed type is suggested as the first step to better planification of a treatment programme. Further, the consideration of other factors, such as gender, comorbidities, treatments received at the acute phase of infection for onset-associated COVID-19 symptoms, factors during hospitalization or the presence of emotional disturbances should be implemented into a treatment programme. Conclusions Accordingly, considering these factors, management of post-COVID pain should include multimodal pharmacological and non-pharmacological modalities targeting emotional/cognitive aspects (i.e. psychological and/or coping strategies), central sensitization-associated mechanisms (i.e. pain neuroscience education), exercise programmes as well as lifestyle interventions (e.g. nutritional support and sleep management). SIGNIFICANCE: This position paper presents an evidence-based clinical reasoning approach for precision management of post-COVID pain.

Sex-related correspondence between mechanical hypersensitivity and the discharge of medullary pain control neurons in neuropathic rats

Here we studied whether the sex-related difference in mechanical hypersensitivity induced by neuropathy is associated with the discharge rate of medullary pain control neurons. We performed experiments in male and female rats with spared nerve injury (SNI) model of peripheral neuropathy. Mechanical hypersensitivity was assessed behaviorally by monofilaments. Discharge rates of pain-control neurons were determined using in vivo single unit recordings under light anesthesia. Recording targets were two medullary nuclei involved in descending pain control: the rostral ventromedial medulla (RVM) and the medullary dorsal reticular nucleus (DRt). Based on the response to peripheral noxious stimulus, neurons were classified as pronociceptive RVM ON-like or DRt neurons, or antinociceptive RVM OFF-like neurons. Behavioral results indicated that the mechanical hypersensitivity induced by SNI was significantly stronger in females than males. The ongoing discharge rates of pronociceptive RVM ON-like neurons were higher and those of antinociceptive RVM OFF-like neurons lower in SNI females than SNI males. Ongoing discharge rates of pronociceptive DRt neurons were not significantly different between SNI females and males. The results suggest that a sex difference in the discharge rate of pain control neurons in the RVM but not DRt may contribute to the maintenance of stronger neuropathic hypersensitivity in females.

Influence of Surface Geometry on Palm and Fist Contact Pressure Distribution During Strikes With the Hand in Automotive Assembly

The increase in repetitive strain injuries to the hand underscores the need for assessing and preventing musculoskeletal overuse associated with hand-intensive tasks. This study investigates the risk of overload injuries in soft tissue structures of the hand by analyzing the pressure distribution and location of peak pressure in the hand during snap-fit connection assembly in the automotive industry. The influence of the surface geometry of automotive trim components the pressure distribution and force imparted during strikes with the palm and the fist are investigated in a cohort of 30 subjects with extensive experience installing trim parts with snap-fit connections. Using the palm or fist (ulnar hand side) of the dominant hand, the subjects struck a simulation device with a flat, rounded, or edged surface geometry. The average peak force applied was 600 N (±122 N), nearly 3 times the force required to overcome the technical resistance of the snap-fit connector (220 N). Fist strikes exerted a 40% higher mean peak pressure and 18% higher mean pressure than did palm strikes. The pressure distribution in the region of the thenar eminence and soft tissue of the ulnar side of the hand did not differ between fist strikes on flat and edged surfaces. Considering the delicate anatomy of the hand, especially the hypothenar muscles on the ulnar side, assembling connection claps using the fist instead of the palm may prevent repetitive blunt trauma to the sensitive blood vessels and nerves in the palm.

Sex specific role of RNA-binding protein, AUF1, on prolonged hypersensitivity after repetitive ischemia with reperfusion injury

Repetitive ischemia with reperfusion (I/R) injury is a common cause of myalgia. I/R injuries occur in many conditions that differentially affect males and females including complex regional pain syndrome and fibromyalgia. Our preclinical studies have indicated that primary afferent sensitization and behavioral hypersensitivity due to I/R may be due to sex specific gene expression in the DRGs and distinct upregulation of growth factors and cytokines in the affected muscles. In order to determine how these unique gene expression programs may be established in a sex dependent manner in a model that more closely mimics clinical scenarios, we utilized a newly developed prolonged ischemic myalgia model in mice whereby animals experience repeated I/R injuries to the forelimb and compared behavioral results to unbiased and targeted screening strategies in male and female DRGs. Several distinct proteins were found to be differentially expressed in male and female DRGs, including AU-rich element RNA binding protein (AUF1), which is known to regulate gene expression. Nerve specific siRNA-mediated knockdown of AUF1 inhibited prolonged hypersensitivity in females only, while overexpression of AUF1 in male DRG neurons increased some pain-like responses. Further, AUF1 knockdown was able to specifically inhibit repeated I/R induced gene expression in females but not males. Data suggests that RNA binding proteins like AUF1 may underlie the sex specific effects on DRG gene expression that modulate behavioral hypersensitivity after repeated I/R injury. This study may aid in finding distinct receptor differences related to the evolution of acute to chronic ischemic muscle pain development between sexes.

Environmental enrichment promotes resilience to neuropathic pain-induced depression and correlates with decreased excitability of the anterior cingulate cortex

Depression is a common comorbidity of chronic pain with many patients being affected. However, efficient pharmacological treatment strategies are still lacking. Therefore, it is desirable to find additional alternative approaches. Environmental enrichment has been suggested as a method to alleviate pain-induced depression. However, the neuronal mechanisms of its beneficial effects are still elusive. The anterior cingulate cortex (ACC) plays a central role in processing pain-related negative affect and chronic pain-induced plasticity in this region correlates with depressive symptoms. We studied the consequences of different durations of environmental enrichment on pain sensitivity and chronic pain-induced depression-like behaviors in a mouse model of neuropathic pain. Furthermore, we correlated the behavioral outcomes to the activity levels of pyramidal neurons in the ACC by analyzing their electrophysiological properties ex vivo. We found that early exposure to an enriched environment alone was not sufficient to cause resilience against pain-induced depression-like symptoms. However, extending the enrichment after the injury prevented the development of depression and reduced mechanical hypersensitivity. On the cellular level, increased neuronal excitability was associated with the depressive phenotype that was reversed by the enrichment. Therefore, neuronal excitability in the ACC was inversely correlated to the extended enrichment-induced resilience to depression. These results suggest that the improvement of environmental factors enhanced the resilience to developing chronic pain-related depression. Additionally, we confirmed the association between increased neuronal excitability in the ACC and depression-like states. Therefore, this non-pharmacological intervention could serve as a potential treatment strategy for comorbid symptoms of chronic pain.

Gender differences in the laryngectomee experience

BACKGROUND

Laryngectomy is a pivotal event in patients. lives, with pervasive and far-reaching effects. Understanding gender differences in these effects may improve care of laryngectomy patients. This paper describes gender differences in the experience after laryngectomy.

AIM

To explore the similarities and differences in the laryngectomee experience based on gender.

METHODS & PROCEDURES

Four gender-matched focus groups were conducted; dialogue was audio recorded, transcribed and studied using interpretative phenomenological analysis (IPA).

OUTCOMES & RESULTS

A total of 17 laryngectomees, eight female and nine male, age range 41-80 years, participated in focus groups. Laryngectomy represented a turning point in the lives of both genders. Four themes emerged: perception of loss, adjusting to alaryngeal communication, finding a positive outlook and re-establishing the self. Themes applied to both genders, with subthemes demonstrating similarities and differences between men and women.

CONCLUSIONS & IMPLICATIONS

Men and women experienced destabilization after laryngectomy related to perceived losses and shifts in identity. Men described navigating from physical disability toward recovery of function, while women described an emotional journey concerning loss and rediscovery of meaning in their lives. Understanding the laryngectomee experience in better detail, which includes recognizing gender differences and rejecting a one-size-fits-all approach, may facilitate more effective preoperative counselling and post-operative support from providers.

WHAT THIS PAPER ADDS

What is already known on the subject Patients who undergo total laryngectomy often struggle with problems with physical, emotional, and social functioning and decreased quality of life. As the literature currently stands, the understanding of the experience of laryngectomees has primarily focused on the perspective of a singular gender. Thus, this is the first qualitative study specifically investigating differences in the laryngectomee experience between men and women. What this paper adds to existing knowledge This study finds that women and men both endorse significant mental and physical changes following laryngectomy; however, their perception of their experience differed by gender. Women endorsed alteration to meaningful life and men demonstrated distress related to loss of physical functioning; both genders described laryngectomy as a formative event that helped them rediscover joy and redefine themselves for the better. What are the potential or actual clinical implications of this work? Our findings suggest men and women have distinct mental and emotional struggles after laryngectomy despite similar physical changes. This suggests that tailoring care with consideration of these gender differences, including preoperative counselling, post-operative support and gender-matched visitors or support groups, may help beneficial in recovery after laryngectomy.

A nationwide survey on producer and veterinarian perceptions of the painfulness of procedures and disease states in dairy and beef cattle

Failure to adequately manage pain in cattle causes suffering and is thus a welfare concern for the livestock industry. The objectives of this study were to summarize caregiver perceptions of the painfulness of various procedures and disease conditions in cattle. This survey also assessed factors that impact the perception of painfulness and determined relationships between pain perception and mitigation in producers and veterinarians in the United States beef and dairy cattle industries. An online survey was distributed via organization listservs and social media groups representing beef and dairy veterinarians and producers. The survey included questions about respondent demographics and pain perception and frequency of pain mitigation use for a variety of common husbandry procedures and disease conditions in cattle less than 2 months, 2-12 months, and greater than 12 months of age. Descriptive statistics were generated, and ordinal logistic regressions were used to assess the relationship between perceived pain level, frequency of pain mitigation use, and respondent demographic factors (e.g., gender, age, and role). There was a relatively low percentage of respondents that identified there was "no pain" associated with the listed procedures and conditions. Across the majority of procedures and conditions and cattle age categories, men perceived procedures to be less painful than women (P < 0.05). Veterinarians and producer-veterinarians perceived procedures to be more painful than producers (P < 0.05) for the majority of procedures and conditions. There were some differences identified between respondent age groups in pain perception but the trends were not consistent across procedures and conditions. There was a significant positive linear trend, with greater perceived pain associated with greater likelihood of providing local and systemic analgesia for all procedures and conditions across all cattle age categories (P ≤ 0.02). Perception of pain is complex and multifactorial, and it influences the likelihood to treat pain in cattle. This research highlighted the importance of understanding how these factors may play a role in increasing the use of pain mitigation within the beef and dairy industries.

Gonadal hormone-dependent nociceptor sensitization maintains nociplastic pain state in female mice

ABSTRACT

Nociplastic pain conditions develop predominantly in women. We recently established a murine nociplastic pain model by applying postinjury thermal (40°C) stimulation to an injured (capsaicin-injected) area, triggering a transition to a nociplastic pain state manifesting as persistent mechanical hypersensitivity outside of the previously injured area. The nociplastic pain state was centrally maintained by spinal microglia in males but peripherally by ongoing afferent activity at the previously injured area in females. Here, we investigated whether gonadal hormones are critical for the development of this peripherally maintained nociplastic pain state in females. Although the transition to a nociplastic pain state still occurred in ovariectomized females, the pain state was maintained neither by ongoing afferent activity at the previously injured area nor by spinal microglia. Estradiol reconstitution a week before the injury plus postinjury stimulation, but not after the transition had already occurred, restored the development of peripherally maintained nociplastic mechanical hypersensitivity in ovariectomized females. G protein-coupled estrogen receptor antagonism during the transition phase mimicked ovariectomy in gonad-intact females, whereas the receptor antagonism after the transition gradually alleviated the nociplastic mechanical hypersensitivity. At the previously injured area, afferents responsive to allyl isothiocyanate (AITC), a TRPA1 agonist, contributed to the maintenance of nociplastic mechanical hypersensitivity in gonad-intact females. In ex vivo skin-nerve preparations, only AITC-responsive afferents from the nociplastic pain model in gonad-intact females showed ongoing activities greater than control. These results suggest that gonadal hormones are critical for peripherally maintained nociplastic pain state in females by sensitizing AITC-responsive afferents to be persistently active.

The complexities of the sleep-pain relationship in adolescents: A critical review

Chronic pain is a common and disabling condition in adolescents. Disturbed sleep is associated with many detrimental effects in adolescents with acute and chronic pain. While sleep and pain are known to share a reciprocal relationship, the sleep-pain relationship in adolescence warrants further contextualization within normally occurring maturation of several biopsychological processes. Since sleep and pain disorders begin to emerge in early adolescence and are often comorbid, there is a need for a comprehensive picture of their interrelation especially related to temporal relationships and mechanistic drivers. While existing reviews provide a solid foundation for the interaction between disturbed sleep and pain in youth, we will extend this review by highlighting current methodological challenges for both sleep and pain assessments, exploring the recent evidence for directionality in the sleep-pain relationship, reviewing potential mechanisms and factors underlying the relationship, and providing direction for future investigations. We will also highlight the potential role of digital technologies in advancing the understanding of the sleep and pain relationship. Ultimately, we anticipate this information will facilitate further research and inform the management of pain and poor sleep, which will ultimately improve the quality of life in adolescents and reduce the risk of pain persisting into adulthood.

Biopsychosocial Approach in Identifying Risk Factors of Kinesiophobia in Persons with Subacromial Pain Syndrome and Developing a Clinical Prediction Tool

Introduction

Although the negative effects of kinesiophobia on functional status in subacromial pain syndrome (SAPS) patients are clearly demonstrated, no study examines the risk factors of kinesiophobia in individuals with SAPS from a biopsychosocial perspective. The present study aims to determine the risk factors of kinesiophobia in individuals with SAPS using a biopsychosocial approach. This study also aims to explore the compounding effects of multiple associative risk factors by developing a clinical prediction tool to identify SAPS patients at higher risk for kinesiophobia.

Materials and methods

This cross-sectional study included 549 patients who were diagnosed with SAPS. The Tampa-Scale of Kinesiophobia (TSK) was used to assess kinesiophobia. Visual analog scale (VAS), The Shoulder Pain and Disability Index (SPADI), Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire, the presence of metabolic syndrome, using any non-steroidal anti-inflammatory drugs, Pain Catastrophizing Scale (PCS), Illness Perception Questionnaire-revised (IPQ-R), Hospital Anxiety and Depression Scale (HADS), behavioral pattern of the patient, sociodemographic characteristics, and treatment expectancy were outcome measures.

Results

Thirteen significant risk factors of having kinesiophobia were: VASat rest (≥ 5.2), VASduring activity (≥ 7.1), DASH (≥ 72.1), presence of metabolic syndrome, PCShelplessness (≥ 16.1), IPQ-Rpersonal control (≤ 17.1), IPQ-Rtreatment control (≤ 16.3), HADSdepression (≥ 7.9), avoidance behavior type, being female, educational level (≤ high school), average hours of sleep (≤ 6.8), and treatment expectancy (≤ 6.6). The presence of seven or more risk factors increased the probability of having high level of kinesiophobia from 34.3 to 51%.

Conclusions

It seems necessary to address these factors, increase awareness of health practitioners and individuals.

Level of evidence

Level IV.

Sex and gender differences in pain

Chronic pain affects 20% of adults and is one of the leading causes of disability worldwide. Women and girls are disproportionally affected by chronic pain. About half of chronic pain conditions are more common in women, with only 20% having a higher prevalence in men. There are also sex and gender differences in acute pain sensitivity. Pain is a subjective experience made up of sensory, cognitive, and emotional components. Consequently, there are multiple dimensions through which sex and gender can influence the pain experience. Historically, most preclinical pain research was conducted exclusively in male animals. However, recent studies that included females have revealed significant sex differences in the physiological mechanisms underlying pain, including sex specific involvement of different genes and proteins as well as distinct interactions between hormones and the immune system that influence the transmission of pain signals. Human neuroimaging has revealed sex and gender differences in the neural circuitry associated with pain, including sex specific brain alterations in chronic pain conditions. Clinical pain research suggests that gender can affect how an individual contextualizes and copes with pain. Gender may also influence the susceptibility to develop chronic pain. Sex and gender biases can impact how pain is perceived and treated clinically. Furthermore, the efficacy and side effects associated with different pain treatments can vary according to sex and gender. Therefore, preclinical and clinical research must include sex and gender analyses to understand basic mechanisms of pain and its relief, and to develop personalized pain treatment.

Estrogenic impregnation alters pain expression: analysis through functional neuropeptidomics in a surgical rat model of osteoarthritis

PURPOSE

Several observational studies suggest that estrogens could bias pain perception. To evaluate the influence of estrogenic impregnation on pain expression, a prospective, randomized, controlled, blinded study was conducted in a Sprague-Dawley rat model of surgically induced osteoarthritis (OA).

METHODS

Female rats were ovariectomized and pre-emptive 17β-estradiol (0.025 mg, 90-day release time) or placebo pellets were installed subcutaneously during the OVX procedures. Thirty-five days after, OA was surgically induced on both 17β-estradiol (OA-E) and placebo (OA-P) groups. Mechanical hypersensitivity was assessed by static weight-bearing (SWB) and paw withdrawal threshold (PWT) tests. Mass spectrometry coupled with high-performance liquid chromatography (HPLC-MS) was performed to quantify the spinal pronociceptive neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), bradykinin (BK), somatostatin (SST), and dynorphin-A (Dyn-A).

RESULTS

Compared to control, ovariectomized rats presented higher SP (P = 0.009) and CGRP (P = 0.017) concentrations. OA induction increased the spinal level of SP (+ 33%, P < 0.020) and decreased the release of BK (- 20%, (P < 0.037)). The OA-E rats at functional assessment put more % body weight on the affected hind limb than OA-P rats at D7 (P = 0.027) and D56 (P = 0.033), and showed higher PWT at D56 (P = 0.009), suggesting an analgesic and anti-allodynic effect of 17β-estradiol. Interestingly, the 17β-estradiol treatment counteracted the increase of spinal concentration of Dyn-A (P < 0.016) and CGRP (P < 0.018).

CONCLUSION

These results clearly indicate that 17β-estradiol interfers with the development of central sensitization and confirm that gender dimorphism should be considered when looking at pain evaluation.

Myrtenol Reduces Orofacial Nociception and Inflammation in Mice Through p38-MAPK and Cytokine Inhibition

Orofacial pain is one of the commonest and most complex complaints in dentistry, greatly impairing life quality. Preclinical studies using monoterpenes have shown pharmacological potential to treat painful conditions, but the reports of the effects of myrtenol on orofacial pain and inflammation are scarce. The aim of this study was to evaluate the effect of myrtenol in experimental models of orofacial pain and inflammation. Orofacial nociceptive behavior and the immunoreactivity of the phosphorylated p38 (P-p38)-MAPK in trigeminal ganglia (TG) and spinal trigeminal subnucleus caudalis (STSC) were determined after the injection of formalin in the upper lip of male Swiss mice pretreated with myrtenol (12.5 and 25 mg/kg, i.p.) or vehicle. Orofacial inflammation was induced by the injection of carrageenan (CGN) in the masseter muscle of mice pretreated with myrtenol (25 and 50 mg/kg, i.p.) or its vehicle (0.02% Tween 80 in saline). Myeloperoxidase (MPO) activity and histopathological changes in the masseter muscle and interleukin (IL)-1β levels in the TG and STSC were measured. The increase in face-rubbing behavior time induced by formalin and P-p38-MAPK immunostaining in trigeminal ganglia were significantly reduced by myrtenol treatment (12.5 and 25 mg/kg). Likewise, increased MPO activity and inflammatory histological scores in masseter muscle, as well as augmented levels of IL-1β in the TG AND STSC, observed after CGN injection, were significantly decreased by myrtenol (25 and 50 mg/kg). Myrtenol has potential to treat orofacial inflammation and pain, which is partially related to IL-1β levels in the trigeminal pathway and p38-MAPK modulation in trigeminal ganglia.

Neurobiological antecedents of multisite pain in children

ABSTRACT

Altered brain structure and function is evident in adults with multisite chronic pain. Although many such adults trace their pain back to childhood, it has been difficult to disentangle whether central nervous system alterations precede or are consequences of chronic pain. If the former is true, aberrant brain activity may identify children vulnerable to developing chronic pain later in life. We examined structural and functional brain magnetic resonance imaging metrics in a subset of children from the first 2 assessments of the Adolescent Brain and Cognitive Development Study. Children (aged 9-10) who were pain free at baseline and then developed multisite pain 1 year later (n = 115) were matched to control children who were pain free at both timepoints (n = 230). We analyzed brain structure (cortical thickness and gray matter volume) and function (spontaneous neural activity and functional connectivity). Results were deemed significant at the cluster level P < 0.05 false discovery rate corrected for multiple comparisons. At baseline, children who subsequently developed multisite pain had increased neural activity in superior parietal /primary somatosensory and motor cortices and decreased activity in the medial prefrontal cortex. They also exhibited stronger functional connectivity between the salience network, somatosensory, and default mode network regions. No significant differences in the brain structure were observed. Increased neural activity and functional connectivity between brain regions, consistent to that seen in adults with chronic pain, exist in children before developing multisite pain. These findings may represent a neural vulnerability to developing future chronic pain.

Mechanisms Underlying Lumbopelvic Pain During Pregnancy: A Proposed Model

Up to 86% of pregnant women will have lumbopelvic pain during the 3rd trimester of pregnancy and women with lumbopelvic pain experience lower health-related quality of life during pregnancy than women without lumbopelvic pain. Several risk factors for pregnancy-related lumbopelvic pain have been identified and include history of low back pain, previous trauma to the back or pelvis and previous pregnancy-related pelvic girdle pain. During pregnancy, women go through several hormonal and biomechanical changes as well as neuromuscular adaptations which could explain the development of lumbopelvic pain, but this remains unclear. The aim of this article is to review the potential pregnancy-related changes and adaptations (hormonal, biomechanical and neuromuscular) that may play a role in the development of lumbopelvic pain during pregnancy. This narrative review presents different mechanisms that may explain the development of lumbopelvic pain in pregnant women. A hypotheses-driven model on how these various physiological changes potentially interact in the development of lumbopelvic pain in pregnant women is also presented. Pregnancy-related hormonal changes, characterized by an increase in relaxin, estrogen and progesterone levels, are potentially linked to ligament hyperlaxity and joint instability, thus contributing to lumbopelvic pain. In addition, biomechanical changes induced by the growing fetus, can modify posture, load sharing and mechanical stress in the lumbar and pelvic structures. Finally, neuromuscular adaptations during pregnancy include an increase in the activation of lumbopelvic muscles and a decrease in endurance of the pelvic floor muscles. Whether or not a causal link between these changes and lumbopelvic pain exists remains to be determined. This model provides a better understanding of the mechanisms behind the development of lumbopelvic pain during pregnancy to guide future research. It should allow clinicians and researchers to consider the multifactorial nature of lumbopelvic pain while taking into account the various changes and adaptations during pregnancy.

Dorsal horn neuronal sparing predicts the development of at-level mechanical allodynia following cervical spinal cord injury in mice

Spinal cord injury (SCI) frequently results in immediate and sustained neurological dysfunction, including intractable neuropathic pain in approximately 60-80% of individuals. SCI induces immediate mechanical damage to spinal cord tissue followed by a period of secondary injury in which tissue damage is further propagated, contributing to the development of anatomically unique lesions. Variability in lesion size and location influences the degree of motor and sensory dysfunction incurred by an individual. We predicted that variability in lesion parameters may also explain why some, but not all, experimental animals develop mechanical sensitivity after SCI. To characterize the relationship of lesion anatomy to mechanical allodynia, we utilized a mouse cervical hemicontusion model of SCI that has been shown to lead to the development and persistence of mechanical allodynia in the ipsilateral forelimb after injury. At four weeks post-SCI, the numbers and locations of surviving neurons were quantified along with total lesion volume and nociceptive fiber sprouting. We found that the subset of animals exhibiting mechanical allodynia had significantly increased neuronal sparing in the ipsilateral dorsal horn around the lesion epicenter compared to animals that did not exhibit mechanical allodynia. Additionally, we failed to observe significant differences between groups in nociceptive fiber density in the dorsal horn around the lesion epicenter. Notably, we found that impactor probe displacement upon administration of the SCI surgery was significantly lower in sensitive animals compared with not-sensitive animals. Together, our data indicate that lesion severity negatively correlates with the manifestation of at-level mechanical hypersensitivity and suggests that sparing of dorsal horn neurons may be required for the development of neuropathic pain.

Attachment voices promote safety learning in humans: A critical role for P2

Humans have evolved to seek the proximity of attachment figures during times of threat in order to obtain a sense of safety. In this context, we examined whether or not the voice of an intimate partner (termed "attachment voice") could reduce fear-learning of conditioned stimuli (CS+) and enhance learning of safety signals (CS-). Although the ability to learn safety signals is vital for human survival, few studies have explored how attachment voices affect safety learning. To test our hypothesis, we recruited thirty-five young couples and performed a classic Pavlovian conditioning experiment, recording behavioral and electroencephalographic (EEG) data. The results showed that compared with a stranger's voice, the voices of the partners reduced expectancy of the unconditioned stimulus (a shock) during fear-conditioning, as well as the magnitude of P2 event-related potentials within the EEG responses, provided the voices were safety signals. Additionally, behavioral and EEG responses to the CS+ and CS- differed more when the participants heard their partner's voice than when they heard the stranger's voice. Thus, attachment voices, even as pure vowel sounds without any semantic information, enhanced acquisition of conditioned safety (CS-). These findings may provide implications for investigating other new techniques to improve clinical treatments for fear- and anxiety-related disorders and for psychological interventions against the mental health effects of the public health emergency.

Postinjury stimulation triggers a transition to nociplastic pain in mice

ABSTRACT

Acute injury-induced pain can transition to chronic nociplastic pain, which predominantly affects women. To facilitate studies on the underlying mechanisms of nociplastic pain, we developed a mouse model in which postinjury thermal stimulation (intermittent 40°C water immersion for 10 minutes at 2 hours postcapsaicin) prolongs capsaicin (ie, experimental injury)-induced transient mechanical hypersensitivity outside of the injury area. Although capsaicin injection alone induced mechanical and thermal hypersensitivity that resolved in ∼7 days (slower recovery in females), the postinjury stimulation prolonged capsaicin-induced mechanical, but not thermal, hypersensitivity up to 3 weeks in both sexes. When postinjury stimulation was given at a lower intensity (30°C) or at later time points (40°C at 1-3 days postcapsaicin), chronification of mechanical hypersensitivity occurred only in females. Similar chronification could be induced by a different postinjury stimulation modality (vibration of paw) or with a different injury model (plantar incision). Notably, the 40°C postinjury stimulation did not prolong capsaicin-induced inflammation in the hind paw, indicating that the prolonged mechanical hypersensitivity in these mice arises without clear evidence of ongoing injury, reflecting nociplastic pain. Although morphine and gabapentin effectively alleviated this persistent mechanical hypersensitivity in both sexes, sexually dimorphic mechanisms mediated the hypersensitivity. Specifically, ongoing afferent activity at the previously capsaicin-injected area was critical in females, whereas activated spinal microglia were crucial in males. These results demonstrate that postinjury stimulation of the injured area can trigger the transition from transient pain to nociplastic pain more readily in females, and sex-dependent mechanisms maintain the nociplastic pain state.

Prevalence and risk factors of musculoskeletal pain symptoms as long-term post-COVID sequelae in hospitalized COVID-19 survivors: a multicenter study

This study investigated the prevalence of long-term musculoskeletal post-COVID pain and their risk factors in a large cohort of COVID-19 survivors. A multicenter cohort study including patients hospitalised due to COVID-19 in five hospitals of Madrid (Spain) during the first wave of the pandemic was conducted. Hospitalisation and clinical data were collected from medical records. Patients were scheduled for a telephone interview after hospital discharge for collecting data about the musculoskeletal post-COVID pain. Anxiety/depressive levels and sleep quality were likewise assessed. From 2,000 patients recruited, a total of 1,969 (46.4% women, age: 61, SD: 16 years) were assessed on average at 8.4 (SD 1.5) months after discharge. At the time of the study, 887 (45% women) reported musculoskeletal post-COVID pain. According to the presence of previous pain symptoms, the prevalence of "de novo" (new-onset) musculoskeletal post-COVID pain was 74.9%, whereas 25.1% experienced an increase of previous symptoms (exacerbated COVID-related pain). Female gender (OR1.349, 95%CI 1.059-1.720), previous history of musculoskeletal pain (OR1.553, 95%CI 1.271-1.898), the presence of myalgia (OR1.546, 95%CI 1.155-2.070) and headache (1.866, 95%CI 1.349-2.580) as COVID-19 associated onset symptoms, and days at hospital (OR1.013, 95%CI 1.004-1.022) were risk factors associated musculoskeletal post-COVID pain. In conclusion, musculoskeletal post-COVID pain is present in 45.1% of COVID-19 survivors at eight months after hospital discharge with most patients developing "de novo" post-COVID pain. Female gender, history of musculoskeletal pain, presence of myalgias and headache as COVID-19 symptoms at the acute phase, and days at hospital were risk factors associated with musculoskeletal post-COVID pain.

Neuron Type-Dependent Synaptic Activity in the Spinal Dorsal Horn of Opioid-Induced Hyperalgesia Mouse Model

Opioids are widely used for pain relief; however, chronic opioid use causes a paradoxical state of enhanced pain sensitivity, termed “Opioid-induced hyperalgesia (OIH).” Despite the clinical importance of OIH, the detailed mechanism by which it enhances pain sensitivity remains unclear. In this study, we tested whether repeated morphine induces a neuronal circuit polarization in the mouse spinal dorsal horn (SDH). Transgenic mice expressing GFP to neurokinin 1 receptor-expressing neurons (sNK1Rn) and GABAergic interneurons (sGABAn) that received morphine [20 mg/kg, once daily for four consecutive days (i.p.)] developed mechanical hypersensitivity. Repeated morphine altered synaptic strengths in the SDH as a specific cell-type but not in a gender-dependent manner. In sNK1Rn and non-tonic firing neurons, repeated morphine treatment significantly increased frequency of spontaneous excitatory postsynaptic current (sEPSC) and evoked EPSC (eEPSC). In addition, repeated morphine treatment significantly decreased evoked inhibitory postsynaptic current (eIPSC) in sNK1Rn. Conversely, in sGABAn and tonic firing neurons, repeated morphine treatment significantly decreased sEPSC frequency and eEPSC, but had no change of eIPSC in sGABAn. Interestingly, repeated morphine treatment significantly decreased neuronal rheobase of sNK1Rn but had no effect on sGABAn. These findings suggest that spinal neuronal circuit polarization maybe the mechanism of OIH and identify a potential therapeutic mechanism to prevent or treat opioid-induced pain.

Sexually Dimorphic Expression of Fear-conditioned Analgesia in Rats and Associated Alterations in the Endocannabinoid System in the Periaqueductal Grey

The endocannabinoid system within the periaqueductal grey (PAG) has been implicated in fear-conditioned analgesia (FCA), the profound suppression of pain upon re-exposure to a context previously paired with an aversive stimulus. Since the endocannabinoid and nociceptive systems exhibit sexual dimorphism, the aim of the present study was to assess possible sex differences in the expression of FCA, fear in the presence of nociceptive tone, and associated sex-dependent alterations in the endocannabinoid system within the PAG. Male and female Sprague-Dawley rats received footshock (10 × 1s; 0.4 mA; every 60 s) or no-footshock in a conditioning arena and 23.5 h later received intraplantar injection of formalin (2.5%) under brief isoflourane anaesthetic into the right hind paw. Nociceptive and fear-related behaviours were assessed 30 min later. Levels of endocannabinoids, N-acylethanolamines and neurotransmitters in the PAG were assessed by LC-MS/MS and expression of endocannabinoid system-related proteins by Western immunoblotting. Male, but not female, rats exhibited robust FCA and greater expression of fear-related behaviours than females. Fear-conditioned formalin-treated males, but not females, had higher levels of N-oleoylethanolamine (OEA) and γ-aminobutyric acid (GABA) in the PAG, compared with non-fear-conditioned controls. There was no effect of fear conditioning on the levels of FAAH or CB₁ receptor expression (CB1R) in the PAG of male or female formalin-treated rats. Non-fear-conditioned females had higher levels of CB1R and PPARγ expression than non-fear-conditioned male counterparts. In summary, our results provide evidence of sexual dimorphism in the expression of FCA and fear-related behaviours, and associated alterations in components of the endocannabinoid system and GABA within the PAG.

Time course prevalence of post-COVID pain symptoms of musculoskeletal origin in patients who had survived to severe acute respiratory syndrome coronavirus 2 infection: a systematic review and meta-analysis

ABSTRACT

The aim of this review or meta-analysis is to synthesize the prevalence of post-coronavirus disease (COVID) pain symptoms of musculoskeletal origin in hospitalized or nonhospitalized patients recovered from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. MEDLINE, CINAHL, PubMed, EMBASE, and Web of Science databases, as well as medRxiv and bioRxiv preprint servers were searched up to May 1, 2021. Studies or preprints reporting data on post-COVID pain symptoms such as myalgias, arthralgias, or chest pain after SARS-CoV-2 infection and collected by personal, telephonic, or electronical interview were included. The methodological quality of the studies was assessed using the Newcastle-Ottawa Scale. Random-effects models were used for meta-analytical pooled prevalence of each post-COVID musculoskeletal pain symptom. Data synthesis was categorized at onset or hospital admission and at 30, 60, and 90, and ≥180 days after. From a total of 12,123 studies identified, 27 peer-reviewed studies and 6 preprints were included. The sample included 14,639 hospitalized and 11,070 nonhospitalized COVID-19 patients. The methodological quality of almost 70% studies was fair. The overall prevalence of post-COVID myalgia, joint pain, and chest pain ranged from 5.65% to 18.15%, 4.6% to 12.1%, and 7.8% to 23.6%, respectively, at different follow-up periods during the first year postinfection. Time trend analysis showed a decrease prevalence of musculoskeletal post-COVID pain from the symptom's onset to 30 days after, an increase 60 days after, but with a second decrease ≥180 days after. This meta-analysis has shown that almost 10% of individuals infected by SARS-CoV-2 will suffer from musculoskeletal post-COVID pain symptomatology at some time during the first year after the infection.

The anatomy of pain and suffering in the brain and its clinical implications

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Chronic pain, with a prevalence of 20-30 % is the major cause of human suffering worldwide, because effective, specific and safe therapies have yet to be developed. It is unevenly distributed among sexes, with women experiencing more pain and suffering. Chronic pain can be anatomically and phenomenologically dissected into three separable but interacting pathways, a lateral 'painfulness' pathway, a medial 'suffering' pathway and a descending pain inhibitory pathway. One may have pain(fullness) without suffering and suffering without pain(fullness). Pain sensation leads to suffering via a cognitive, emotional and autonomic processing, and is expressed as anger, fear, frustration, anxiety and depression. The medial pathway overlaps with the salience and stress networks, explaining that behavioural relevance or meaning determines the suffering associated with painfulness. Genetic and epigenetic influences trigger chronic neuroinflammatory changes which are involved in transitioning from acute to chronic pain. Based on the concept of the Bayesian brain, pain (and suffering) can be regarded as the consequence of an imbalance between the two ascending and the descending pain inhibitory pathways under control of the reward system. The therapeutic clinical implications of this simple pain model are obvious. After categorizing the working mechanisms of each of the available treatments (pain killers, psychopharmacology, psychotherapy, neuromodulation, psychosurgery, spinal cord stimulation) to 1 or more of the 3 pathways, a rational combination can be proposed of activating the descending pain inhibitory pathway in combination with inhibition of the medial and lateral pathway, so as to rebalance the pain (and suffering) pathways.

Treatment Strategies for Generator Pocket Pain

OBJECTIVE

Generator site pain is a relatively common phenomenon in patients undergoing spinal cord stimulation (SCS) that complicates management and effective pain relief. This pain may be managed conservatively, with repositioning of the battery and, in some cases, with explant. Here we explore our experience with management of generator site pain ("pocket pain") in a large single-center study.

METHODS

All SCS permanent implants and implantable pulse generator (IPG) placements over 9 years were reviewed. Of 785 cases, we identified 43 patients with pocket pain (5.5%). Demographics and treatments of the pocket pain cohort were analyzed.

RESULTS

The mean age (± SEM) of the pocket pain cohort was 46.86 ± 1.06, and there were 10/33 males/females. Females were overrepresented in pocket pain cohort (76.7%) when compared with the total SCS cohort (59.0%) (X2 = 5.93, P = 0.015). Diagnosis included failed back surgery syndrome (51.2%), complex regional pain syndrome (23.3%), and chronic neuropathic pain (25.5%). No patients improved with conservative therapy. All patients either went on to revision (n = 23) or explant (n = 20). Time from initial surgery to development of pocket pain was 7.5 months (range: 0.3-88) and from pocket pain to revision surgery was 4.5 months (range: 0.4-26). In addition, significantly more pocket pain patients (65.1%) had workers' compensation (WC) insurance compared with patients without pocket pain (24.9%) (X2 = 33.3, P < 0.001).

CONCLUSION

In our institutional experience, pocket pain was inadequately managed with conservative treatments. Being female and having SCS filed under WC increased risk of pocket pain. Future work will explore the nuances in device placement based on body shape and manual activity responsibilities.

Female Gender Is Associated with a Higher Prevalence of Chronic Neck Pain, Chronic Low Back Pain, and Migraine: Results of the Spanish National Health Survey, 2017

OBJECTIVES

To assess the prevalence of chronic neck pain (CNP), chronic low back pain (CLBP), and migraine headache (MH) in the Spanish population and to identify sociodemographic and health-related variables associated with CNP, CLBP, and MH.

DESIGN

Observational study.

SETTING

Spain.

SUBJECTS

A total of 22,511 persons 18 years of age or older (10,304 males and 12,207 females) who participated in the 2017 Spanish National Health Survey.

METHODS

Stratified three-stage sampling was applied. CNP, CLBP, and MH were the dependent variables. The analysis was conducted separately by gender. Sociodemographic features, self-perceived health status, lifestyle habits, comorbidities, and pain features were analyzed by using logistic regression models.

RESULTS

Females reported a higher prevalence of CNP, CLBP, and MH (P < 0.001) than males. For both sexes, anxiety and/or depression and poor self-rated health were associated with a significantly increased prevalence of CNP, CLBP, and MH. For CNP and CLBP, the identified associated factors were older age and limitations to usual activity. For CNP and MH, the most common associated factor was comorbid respiratory disease.

CONCLUSIONS

Our study identified several factors associated with CNP, CLBP, and MH in Spanish female and male adults, with potential implications for health care providers.

Phenotyping peripheral neuropathic pain in male and female adolescents: pain descriptors, somatosensory profiles, conditioned pain modulation, and child-parent reported disability

ABSTRACT

Neuropathic pain (NeuP) can be difficult to diagnose and manage in children. Data regarding prevalence and sex-dependent differences are limited, and more detailed phenotyping is needed. This observational cohort study recruited adolescents (10-17 years) with NeuP or complex regional pain syndrome (CRPS). After pain history and NeuP questionnaires, quantitative sensory testing was performed. Individual z-score plots were calculated with body-region control measures and matched to mechanism-related sensory profiles (sensory loss, thermal hyperalgesia, and mechanical hyperalgesia). Conditioned pain modulation was assessed with pressure pain threshold and a contralateral cold conditioning stimulus, and meaningful conditioned pain modulation defined as twice the standard error of measurement. Patients and parents completed validated questionnaires for child quality of life (QoL), pain catastrophizing, and self-reported anxiety/depression. Males (n = 23) and females (n = 43) with NeuP (n = 52) or CRPS (n = 14) reported moderate-severe pain with neuropathic sensory descriptors. Mixed patterns of sensory gain/loss at pain sites were not sex-dependent. Thermal hyperalgesia was common in both NeuP and CRPS, whereas sensory loss occurred only with NeuP and in a smaller proportion than adult cohorts. Conditioned pain modulation was inhibitory in 54%, facilitatory in 14%, and nonresponders had variable cold conditioning sensitivity. Males and females reported marked impairment of QoL, increased emotional distress, and pain catastrophising. Child-parent QoL scores correlated, but catastrophizing scores were discordant when parents or adolescents reported higher anxiety/depression. NeuP in adolescents is associated with significant pain, physical impairment, and psychosocial impairment. Quantifying alterations in somatosensory profiles, descending modulation, child and parent psychological function will inform individualized therapy and stratification for future clinical trials.

Periaqueductal gray/dorsal raphe dopamine neurons contribute to sex differences in pain-related behaviors

Sex differences in pain severity, response, and pathological susceptibility are widely reported, but the neural mechanisms that contribute to these outcomes remain poorly understood. Here we show that dopamine (DA) neurons in the ventrolateral periaqueductal gray/dorsal raphe (vlPAG/DR) differentially regulate pain-related behaviors in male and female mice through projections to the bed nucleus of the stria terminalis (BNST). We find that activation of vlPAG/DRDA+ neurons or vlPAG/DRDA+ terminals in the BNST reduces nociceptive sensitivity during naive and inflammatory pain states in male mice, whereas activation of this pathway in female mice leads to increased locomotion in the presence of salient stimuli. We additionally use slice physiology and genetic editing approaches to demonstrate that vlPAG/DRDA+ projections to the BNST drive sex-specific responses to pain through DA signaling, providing evidence of a novel ascending circuit for pain relief in males and contextual locomotor response in females.

Increased expression of dendrin in the dorsal horn of the spinal cord during stress is regulated by sex hormones

Chronic stress has various effects on organisms and is sex-specific. The aim of the study was to describe the expression of synapse strengthening protein, dendrin, in the spinal cord (SC) and the dependence of its expression on chronic stress and sex hormones. Thirteen-month-old female and male rats were castrated (ovariectomy [F-OVX] or orchidectomy [M-ORX]) or sham-operated (F-SH or M-SH), respectively. At age 15 months, three 10-day-sessions of sham stress (control, C) or chronic stress (S) were conducted. Dendrin expression was present in the thoracic SC segments and the dorsal root ganglia (DRG). In the SC, dendrin expression was prominent in superficial laminae of the dorsal horn and lamina X (central canal). The M-ORX-S group had the highest dendrin expression in the dorsal horn, being significantly higher than the M-ORX-C or M-SH-S groups (P < 0.05). Dendrin expression was significantly higher in the F-SH-S group than the F-SH-C group (P < 0.05), as well as in the F-SH-S than the M-SH-S (P < 0.05). Co-localization with the α-d-galactosyl-specific isolectin B4 (IB4) in central projections of the DRG neurons in the dorsal horn of the SC was 7.43 ± 3.36%, while with the calcitonin gene-related peptide (CGRP) was 8.47 ± 4.45%. Localization of dendrin was observed in soma and nuclei of neurons in the dorsal horn. Dendrin expression in pain-processing areas of the SC, the DRG neurons and their peripheral projections suggest possible roles in pain perception and modulation. Stress-induced increase in dendrin expression and its dependence on sex hormones may partially explain sex-specific pain hypersensitivity induced by stress.

Pain in Women: A Perspective Review on a Relevant Clinical Issue that Deserves Prioritization

Introduction

Gender equity and gender medicine are opportunities not to be missed, and this Expert Group Opinion Paper on pain in women aims to review the treatment of pain conditions mainly affecting women, as well as the fundamental aspects of the different clinical response to drug treatment between the genders, and what can be done for gender-specific rehabilitation.

Methods

Perspective review.

Results

Genotypic and phenotypic differences in pain between the sexes are conditioned by anatomical, physiological, neural, hormonal, psychological, social, and cultural factors, such as the response to pharmacological treatment to control pain. The examination of these factors shows that women are affected by pain diseases more frequently and severely than men and that they report pain more frequently and with a lower pain threshold than men. Some forms of pain are inherently related to gender differences, such as pain related to the genitourinary system. However, other forms of chronic pain are seen more frequently in women than men, such as migraine, rheumatological, and musculoskeletal pain, in particular fibromyalgia.

Discussion

Research is needed into the pathophysiological basis for gender differences in the generation of acute pain and maintenance of chronic pain, including the factors that put women at higher risk for developing chronic pain. In addition, different specialties need to collaborate to develop gender-related diagnostic and therapeutic guidelines, and healthcare professionals need to upskill themselves in the appropriate management of pain using existing diagnostic tools and therapeutic options.

Sex Differences in Clinical Outcomes Following Surgical Treatment of Femoroacetabular Impingement

BACKGROUND

Sex-based differences in clinical outcomes following surgical treatment of femoroacetabular impingement remain largely uncharacterized; this prospective, multicenter study evaluated these differences both directly and adjusted for covariates.

METHODS

Hips undergoing surgical treatment of symptomatic femoroacetabular impingement were prospectively enrolled in a multicenter cohort. Patient demographics, radiographic parameters, intraoperatively assessed disease severity, and history of surgical procedures, as well as patient-reported outcome measures, were collected preoperatively and at a mean follow-up of 4.3 years. A total of 621 (81.6%) of 761 enrolled hips met the minimum 1 year of follow-up and were included in the analysis; 56.7% of analyzed hips were female. Univariate and multivariable statistics were utilized to assess the direct and adjusted differences in outcomes, respectively.

RESULTS

Male hips had greater body mass index and larger α angles. Female hips had significantly lower preoperative and postoperative scores across most patient-reported outcome measures, but also had greater improvement from preoperatively to postoperatively. The preoperative differences between sexes exceeded the threshold for the minimal clinically important difference of the modified Harris hip score (mHHS) and all Hip disability and Osteoarthritis Outcome Score (HOOS) domains except quality of life. Preoperative sex differences in mHHS, all HOOS domains, and Short Form-12 Health Survey physical function component score were greater than the postoperative differences. A greater proportion of female hips achieved the minimal clinically important difference for the mHHS, but male hips were more likely to meet the patient acceptable symptom state for this outcome. After adjusting for relevant covariates with use of multiple regression analysis, sex was not identified as an independent predictor of any outcome. Preoperative patient-reported outcome scores were a strong and highly significant predictor of all outcomes.

CONCLUSIONS

Significant differences in clinical outcomes were observed between sexes in a large cohort of hips undergoing surgical treatment of femoroacetabular impingement. Despite female hips exhibiting lower baseline scores, sex was not an independent predictor of outcome or reoperation.

LEVEL OF EVIDENCE

Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Sexual Dimorphism in the Expression of Pain Phenotype in Preclinical Models of Rheumatoid Arthritis

Rheumatoid arthritis is one of most frequent rheumatic diseases, affecting around 1% of the population worldwide. Pain impacting the quality of life for the patient with rheumatoid arthritis, is often the primary factor leading them to seek medical care. Although sex-related differences in humans and animal models of rheumatoid arthritis are described, the correlation between pain and sex in rheumatoid arthritis has only recently been directly examined. Here we review the literature and explore the mechanisms underlying the expression of the pain phenotype in females and males in preclinical models of rheumatoid arthritis.

The burden of early life stress on the nociceptive system development and pain responses

For a long time, the capacity of the newborn infant to feel pain was denied. Today it is clear that the nociceptive system, even if still immature, is functional enough in the newborn infant to elicit pain responses. Unfortunately, pain is often present in the neonatal period, in particular in the case of premature infants which are subjected to a high number of painful procedures during care. These are accompanied by a variety of environmental stressors, which could impact the maturation of the nociceptive system. Therefore, the question of the long-term consequences of early life stress is a critical question. Early stressful experience, both painful and non-painful, can imprint the nociceptive system and induce long-term alteration in brain function and nociceptive behavior, often leading to an increase sensitivity and higher susceptibility to chronic pain. Different animal models have been developed to understand the mechanisms underlying the long-term effects of different early life stressful procedures, including pain and maternal separation. This review will focus on the clinical and preclinical data about early life stress and its consequence on the nociceptive system.

Cluster headache is one of the most intensely painful human conditions: Results from the International Cluster Headache Questionnaire

OBJECTIVE

To determine the pain intensity of cluster headache through a large survey by comparing it to other painful disorders. Furthermore, to investigate the relationship between maximal pain, autonomic, and other clinical symptoms, as well as demographic attributes of cluster headache.

BACKGROUND

The pain of cluster headache is anecdotally considered to be one of the worst pains in existence. The link between pain and autonomic features of cluster headache is understood mechanistically through the trigeminovascular reflex, though it is not clear if this is a graded response. Links between pain and other features of cluster headache are less well understood.

METHODS

This Internet-based cross-sectional survey included questions on cluster headache diagnostic criteria, which were used as part of the inclusion/exclusion criteria for the study. Respondents were asked to rate a cluster headache attack on the 0-10 numerical rating scale. Additionally, they were asked if they had experienced a list of other painful conditions such as labor pain or nephrolithiasis; if so they were asked to rate that pain as well. The survey also included demographics, mood scores, and treatment responses.

RESULTS

A total of 1604 cluster headache respondents were included in the analysis. Respondents rated cluster headache as significantly (p < 0.001) more intense than every other pain condition examined. Cluster headache attacks were rated as 9.7 ± 0.6 (mean ± standard deviation) on the numerical rating scale, followed by labor pain (7.2 ± 2.0), pancreatitis (7.0 ± 1.5), and nephrolithiasis (6.9 ± 1.9). The majority of cluster headache respondents rated a cluster headache attack at maximal or 10.0 pain (72.1%, 1157/1604). Respondents with maximal pain were statistically significantly more likely to have cranial autonomic features compared to respondents with less pain: conjunctival injection or lacrimation 91% (1057/1157) versus 85% (381/447), eyelid edema 77% (887/1157) versus 66% (293/447), forehead/facial sweating 60% (693/1157) versus 49% (217/447), fullness in the ear 47% (541/1157) versus 35% (155/447), and miosis/ptosis 85% (1124/1157) versus 75% (426/447) (all p values <0.001). Respondents with maximal pain also had other statistically significant findings: more frequent attacks (4.0 ± 2.0 attacks per day vs. 3.5 ± 2.0 attacks per day), higher Hopelessness Depression Symptom Questionnaire scores (24.5 ± 16.9 vs. 21.1 ± 15.2), decreased overall effectiveness from calcium channel blockers (on a 5-point Likert scale), and more likely female: 34% (389/1157) versus 24% (108/447) (all p values <0.001). Pain intensity was not associated with restlessness, headache duration, age of onset, episodic/chronic status, or the effectiveness of any acute or preventive medication other than calcium channel blockers.

CONCLUSIONS

Cluster headache is an intensely painful disorder, even in the context of other disorders considered intensely painful. Maximal pain intensity is associated with more cranial autonomic features, suggesting a graded response between pain and autonomic features. Maximal pain intensity is also associated with headache frequency but not duration, suggesting a relationship between pain intensity and mechanisms controlling headache onset, but not between pain intensity and mechanisms controlling headache offset.

Sex and gender differences in anesthesia: Relevant also for perioperative safety?

Sex (a biological determination) and gender (a social construct) are not interchangeable terms and both impact perioperative management and patient safety. Sex and gender differences in clinical phenotypes of chronic illnesses and risk factors for perioperative morbidity and mortality are relevant for preoperative evaluation and optimization. Sex-related differences in physiology, as well as in pharmacokinetics and pharmacodynamics of anesthetic drugs may influence the anesthesia plan, the management of pain, postoperative recovery, adverse effects, patient satisfaction, and outcomes. Further studies are needed to characterize outcome differences between men and women in non-cardiac, cardiac, and transplantation surgery in order to individualize perioperative management and improve patient safety. Transgender patients represent a vulnerable population who need special perioperative care. Gender balance increases team performance and may improve perioperative outcomes.

Nociceptive, emotional, electrophysiological, and histological characterization of the chronic constriction injury model in female Wistar Han rats

Chronic neuropathic pain affects 7-10 % of the population and is often accompanied by comorbid emotional disorders, which greatly reduce the quality of life of the patients, impairing physical, cognitive, emotional, and social functioning. Despite the higher prevalence and severity of chronic pain in women, the number of publications using female animals remains scarce. While in the chronic constriction injury (CCI) model the development of mechanical/thermal hyperalgesia, allodynia and spontaneous pain has been shown in both sexes, little is known on CCI-induced emotional impairments and sciatic nerve histopathology in female rats, as well as on the contributions of ovarian hormones to peripheral nerve injury. In this work, young adult rats (Wistar Han) were assigned to one of five groups: gonadally intact females (SHAM/SHAM), ovariectomized females (SHAM/OVX), gonadally intact females with CCI (CCI/SHAM); ovariectomized females with CCI (CCI/OVX) and males with CCI (CCI_M). In the postoperative period, CCI animals, both females and males, displayed visible gait abnormalities, limping and guarding the affected hind paw although locomotion was not affected. Neuropathic females developed sustained mechanical allodynia, with CCI/OVX animals displaying symptoms two weeks before CCI/SHAM females. Interestingly, regarding mechanical and cold allodynia, CCI males slowly recovered from week 3 onwards. While CCI induced neither anxiety- nor depressive-like behaviour in females, ovariectomy per se induced anhedonic-like behaviour, regardless of CCI surgery. Histopathological analysis of the sciatic nerve showed CCI induced nerve damage, fibrosis, myelin sheath degradation and inflammation. Single-cell electrophysiological data from the rostral ventromedial medulla (RVM) suggests this area is partly involved in descending facilitation associated with experimental neuropathic pain. Altogether, our findings demonstrate CCI females display distinct sensory, emotional, electrophysiological, and histopathological impairments from males, and that ovariectomy aggravates females' responses to peripheral nerve injury.

Pain relief outcomes using an SCS device capable of delivering combination therapy with advanced waveforms and field shapes

BACKGROUND

Given the range of subjective experiences reported by patients with chronic pain, Spinal Cord Stimulation (SCS) systems designed for tailored delivery of analgesic therapy may help improve treatment effectiveness and satisfaction.

RESEARCH DESIGN AND METHODS

This case-series evaluated 420 patients with chronic back and/or leg pain implanted with an SCS device capable of sequential or simultaneous delivery of neurostimulation (i.e. combination therapy) as well as multiple waveforms and/or field shapes. Following implantation, an array of standard programs (e.g. paresthesia-based SCS), and a custom set of sub-perception programs were provided per patient feedback. Pain scores (Numeric Rating Scale, NRS) were collected at baseline and during follow-up.

RESULTS

In this multicenter, observational series (n = 420, 53.1% female; Age: 64.2 ± 13.4 years), a mean overall pain score of 7.2 ± 1.8 (SD) was reported pre-trial (Baseline). At a mean follow-up duration of 208 ± 200 (SD) days, the mean overall pain score reduced to 2.4 (p < 0.0001). Overall pain was reduced by 5.1 ± 2.4 and 4.5 ± 2.4 points (NRS) at 3-months (N = 256) and at 12-months post-implant (N = 122) respectively (p < 0.0001).

CONCLUSIONS

These results suggest that highly 'customizable' SCS approaches may allow for highly effective pain relief within the real-world clinical setting.