Studying sex and gender differences in pain and analgesia: a consensus report

Chronic stress induces wide-spread hyperalgesia: The involvement of spinal CCK1 receptors

Chronic primary pain (CPP) occurs in the absence of tissue injury and includes temporomandibular disorders (TMD), fibromyalgia syndrome (FMS) and irritable bowel syndrome (IBS). CPP is commonly considered a stress-related chronic pain and often presents as wide-spread pain or comorbid pain conditions in different regions of the body. However, whether prolonged stress can directly result in the development of CPP comorbidity remains unclear. In the present study, we adapted a 21 day heterotypic stress paradigm in mice and examined whether chronic stress induced wide-spread hyperalgesia, modeling comorbid CPP in the clinic. We found that chronic stress induced anxiety- and depression-like behaviors, and resulted in long-lasting wide-spread hyperalgesia over several body regions such as the orofacial area, hindpaw, thigh, upper back and abdomen in female mice. We further found that the expression of cholecystokinin (CCK)1 receptors was significantly increased in the L4-L5 spinal dorsal horn of the female mice after 14 and 21 day heterotypic stress compared with the control animals. Intrathecal injection of the CCK1 receptor antagonist CR-1505 blocked pain hypersensitivity in the subcervical body including the upper back, thigh, hindpaw and abdomen. These findings suggest that the upregulation of spinal CCK1 receptors after chronic stress contributes to the central mechanisms underlying the development of wide-spread hyperalgesia, and may provide a potential and novel central target for clinical treatment of CPP.

Is Social Support Associated With Clinical Outcomes in Adults With Nonspecific Chronic Low Back Pain? A Systematic Review

OBJECTIVES

Nonspecific chronic low back pain (NSCLBP) is associated with psychological and social factors such as social support. However, little research has focused on the latter. This article aimed to review the literature on the association between social support and clinical outcomes of patients with NSCLBP, particularly regarding differences in sex, gender, and types of social support.

METHODS

MEDLINE, EMBASE, Web of Science, PsycINFO, and CENTRAL were searched until April 19, 2024, without restrictions of time or language. Eligible articles were observational studies reporting measures of association between social support and clinical outcomes among adults with NSCLBP. Risk of bias was assessed using the QUIPS tool, and findings were analyzed qualitatively. This systematic review was registered on PROSPERO (CRD42022363210).

RESULTS

Of the 3528 identified studies, 11 were included in the review (1290 patients), showing a moderate to high risk of bias. Of the 5 studies showing a significant finding for pain, 4 reported a negative correlation (r=-0.18, -0.32, -0.35, -0.36) and 1 did not report any association index. Of the 6 studies showing a significant finding for disability, 2 reported a negative correlation (r=-0.29, -0.42), 2 reported a positive association (r=0.322; β=0.29), and 2 did not report any association index. No data was available for the investigated subgroups or secondary clinical outcomes.

DISCUSSION

Small associations were found between social support and clinical outcomes of individuals with NSCLBP. Further research is needed to establish its clinical relevance according to types of social support, sex, and gender.

The Role of Pain Expectations in the Development of Secondary Pinprick Hypersensitivity: Behavioral-Neurophysiological Evidence and the Role of Pain-Related Fear

Secondary mechanical hypersensitivity, a common symptom of neuropathic pain, reflects increased responsiveness of nociceptive pathways and can be induced temporarily in healthy volunteers using high-frequency electrical stimulation of the skin. Expectations modulate acute pain perception and fear of pain has been shown to attenuate and amplify the placebo and nocebo effects, respectively. However, the role of expectations and fear in the development of mechanical secondary hypersensitivity remains unclear. The modulatory role of fear and expectations in the development of mechanical secondary hypersensitivity remains so far mainly correlational. Here, we randomly assigned healthy participants (women) to a placebo, nocebo, or control group. In the experimental groups, participants' expectations of pain were manipulated using verbal suggestions accompanied by an inert treatment. Fear of pain was evaluated both in terms of fear of pain and via questionnaires. Sensitivity to mechanical stimulation was assessed by self-reported pinprick ratings before and after high-frequency stimulation; pinprick-evoked potentials elicited by the stimulation were recorded. The placebo group developed the least mechanical secondary hypersensitivity (smaller proximal-distal spread), while the nocebo group developed the most, but only when outliers were excluded. Higher expectations of pain predicted a greater development of mechanical secondary hypersensitivity. Anticipatory pain-related fear only mediated the relationship between unpleasantness expectations and perceived pinprick unpleasantness. Dispositional fear of pain moderated the relationship between expectations and the perceived intensity and unpleasantness of pinpricks. No group differences were observed in pinprick-evoked potentials. We provide preliminary evidence that both expectations and fear impact the development of mechanical secondary hypersensitivity. PERSPECTIVE: Expectations of pain may influence the development of secondary mechanical hypersensitivity. This effect is moderated by dispositional fear of pain and partially mediated by situational fear of pain.

COMT Variants are Associated With Breast and Nipple Pain

Estimates suggest that only 24.9% of infants born in 2019 were exclusively breastfed before 6 months of age, despite the known health benefits of exclusive breastfeeding. Breast and nipple pain is one of the primary determinants of exclusive breastfeeding. Environmental contributions to breastfeeding success have been reported extensively in the literature, but the contribution(s) of maternal genetics has yet to be discovered. The purpose of the study was to identify an association between pain and lactation-related gene variants with exclusive breastfeeding determinants. We selected 4 genes having single nucleotide polymorphisms (SNPs) with potential functional significance in breastfeeding and pain: prolactin receptor (PRLR), oxytocin receptor (OXTR), catechol-O-methyltransferase (COMT), and milk fat globule epidermal growth factor and factor V/VIII domain containing (MFGE8). We performed a cross-sectional secondary analysis of a longitudinal randomized controlled trial study, Promoting Self-Management of Breast and Nipple Pain with Biomarkers and Technology for Breastfeeding Women (NCT05262920). Breast and nipple pain, perceived insufficient milk, and breastfeeding self-efficacy were examined using total scale scores for the Brief Pain Inventory, Visual Analog Scale, H&H Lactation Scale, and the Breastfeeding Self-efficacy Scale-short form, respectively. Of the candidate genes examined, SNPs within COMT were significantly associated with breastfeeding-related outcomes. Specifically, COMT rs4633 and rs4680 minor allele carriers (T, A) reported higher breast and nipple pain intensity than women homozygous for the major allele (C, G). COMT is the most widely researched "pain gene" and has been linked to cold, postoperative, and postpartum pain. This study is the first to identify a contribution of COMT variants to breast and nipple pain and, as a result, to breastfeeding exclusivity. PERSPECTIVE: Two SNPs in the pain gene COMT are associated with breast and nipple pain. Clinically, a minor allele in COMT rs4633 and rs4680 may increase a woman's rating of moderate breast and nipple pain. TRIAL REGISTRATION: PROMPT was registered in ClinicalTrials.gov (protocol #NCT05262920).

Education, gender, and frequent pain among middle-aged and older adults in the United States, England, China, and India

ABSTRACT

Using cross-sectional data from the United States, England, China, and India, we examined the relationship between education and frequent pain, alongside the modification role of gender in this relationship. We further examined patterns of 3 pain dimensions among participants who reported frequent pain, including pain severity, interference with daily activities, and medication use (these pain dimension questions were not administered in all countries). Our analytical sample included 92,204 participants aged 50 years and above. We found a high prevalence of frequent pain across the 4 countries ranging from 28% to 41%. Probit models showed that higher education was associated with lower risk of pain (United States: -0.26, 95% CI: -0.33, -0.19; England: -0.32, 95% CI: -0.39, -0.25; China: -0.33, 95% CI -0.41, -0.26; India: -0.18, 95% CI -0.21, -0.15). Notably, in China and India, the negative association between higher education and frequent pain was less pronounced among women compared with men, which was not observed in the United States or England. Further analysis showed that individuals with higher education experiencing frequent pain reported less severity, fewer daily activity interferences, and less medication use compared with those with lower education. In the United States, these associations were stronger among women. Our findings highlight the prevalent pain among middle-aged and older adults in these 4 countries and emphasize the potentially protective role of higher education on frequent pain, with nuanced gender differences across different settings. This underscores the need for tailored strategies considering educational and gender differences to improve pain management and awareness.

Pressure algometry in the general adult population: Age and sex differences

Experimental pain studies have revealed inter-individual variations in pain perception that are influenced by age, sex, and country of origin. This study aimed to explore the age and sex differences in pressure pain thresholds within the Iranian general population. To assess the pressure pain thresholds, a handheld pressure algometer was applied bilaterally to the middle fingers of both hands. The participants also completed the short form of the McGill Pain Questionnaire to provide a clinical pain rating. This cross-sectional study included 1610 adult subjects (54.96% female, mean age 40.13 ± 10.18 years). The findings indicated that females generally exhibited lower pain thresholds than males when assessing pain detection and tolerance parameters (P < .001). Females also demonstrated a significant lower pressure thresholds and clinical pain ratings compared with men (P < .001). Additionally, significant differences were observed between age groups in terms of pain detection and tolerance thresholds (P = .02 and P = .03, respectively). However, the interaction between sex and age was not significant. No significant differences in pain detection thresholds were observed between the right and left hand (P = .11). This study underscores the potential utility of algometry as a valuable tool for objectifying pain in the Iranian population.

Self-reported pain during different phases of orthodontic treatment with fixed appliance: A multi-centre randomized controlled trial in adolescents with crowding

OBJECTIVES

To compare self-reported pain levels across various treatment phases using passive self-ligating (Damon) and conventional (Victory) standardized fixed appliance systems.

MATERIALS AND METHODS

Adolescents (12-17 years old) with crowding and displaced teeth, planned for non-extraction treatment, were recruited from four orthodontic clinics. They were randomized into stratified blocks (1:1 ratio) using concealed allocation to receive Damon Q™ (34 boys, 28 girls) or Victory™ (39 boys, 31 girls). Pain and analgesic intake were assessed on seven different occasions with validated self-report questionnaires using a 10-grade scale.

RESULTS

Of the 132 patients included, six were lost to follow up. Clinically relevant mean pain scores (≥4) were registered in both groups after bonding upper and lower arches and after insertion of 0.019 × 0.025 stainless steel archwire. The highest mean scores were reported on day two after bonding the upper arch (Damon 5.96, Victory 7.18, P = .011). In both groups, at least 40% reported taking analgesics during various treatment phases. The Damon group reported a lower intake of analgesics on days one and two (P = .042 and .037) after treatment initiation. In the entire sample, boys reported significantly higher mean pain scores than girls on the second and third days after bonding (P = .008 and .026, respectively).

CONCLUSIONS

Lower pain levels were reported from the Damon group after bonding. In general, boys reported higher pain than girls did. Clinicians and adolescents need to be aware that clinically relevant pain levels can be expected not only after bonding but also in later phases.

Uniportal video-assisted thoracic surgery versus open thoracotomy for chronic pain after surgery: a prospective cohort study

PURPOSE

The potential of uniportal video-assisted thoracic surgery (U-VATS) to reduce chronic pain after thoracic surgery (CPTS) compared to open thoracotomy (OT) remains unexplored. This prospective study aims to assess the incidence of CPTS following U-VATS or OT and identify associated risk factors.

METHODS

Patients undergoing thoracic surgery were recruited from March 2021 to March 2022, categorized by surgical approach (U-VATS vs. OT). Standard clinical protocols for surgery, anesthesia, and analgesia were followed. Pain symptoms were assessed using the Short-form McGill Pain Questionnaire, with follow-ups up to 6 months. Perioperative factors influencing CPTS at 3 months were analyzed through univariate and multivariate methods.

RESULTS

A total of 694 patients were analyzed. Acute pain after thoracic surgery (APTS) was significantly less severe in the U-VATS group (p < 0.001). U-VATS patients exhibited a lower incidence of CPTS at 3 months (63.4% vs. 80.1%, p < 0.001), with reduced severity among those experiencing CPTS (p = 0.007) and a decreased occurrence of neuropathic pain (p = 0.014). Multivariate analysis identified OT incision, moderate to severe APTS (excluding moderate static pain at 24 h postoperative), nocturnal surgery, and lung surgery as risk factors for CPTS.

CONCLUSION

This study underscores the potential of U-VATS to reduce both the incidence and severity of CPTS at 3 months compared to OT. Furthermore, it highlights risk factors for CPTS, including OT incision, inadequately managed APTS, lung surgery, and nocturnal surgery. These findings emphasize the importance of considering surgical approach and perioperative pain management strategies to mitigate the burden of CPTS.

Sex differences in mechanisms of pain hypersensitivity

The introduction of sex-as-a-biological-variable policies at funding agencies around the world has led to an explosion of very recent observations of sex differences in the biology underlying pain. This review considers evidence of sexually dimorphic mechanisms mediating pain hypersensitivity, derived from modern assays of persistent pain in rodent animal models. Three well-studied findings are described in detail: the male-specific role of spinal cord microglia, the female-specific role of calcitonin gene-related peptide (CGRP), and the female-specific role of prolactin and its receptor. Other findings of sex-specific molecular involvement in pain are subjected to pathway analyses and reveal at least one novel hypothesis: that females may preferentially use Th1 and males Th2 T cell activity to mediate chronic pain.

Systemic administration of Resolvin D1 reduces cancer-induced bone pain in mice: Lack of sex dependency in pain development and analgesia

AIMS

Bone cancer produces severe pain that is treated with opioids, but serious side effects limit opioid utilization. There is therefore a need to develop effective and safe non-opioid alternatives. The lipid mediator, Resolvin D1 (RvD1), could be a prospective candidate for cancer pain treatment. To assess RvD1 and other potential candidates, appropriate animal models that recapitulate clinical features must be used. Although several preclinical models of cancer pain have been developed, the influence of sex on the development of cancer pain and the effectiveness of RvD1 have not been studied.

RESULTS

Using a mouse model of fibrosarcoma growth in and around the calcaneus bone, we demonstrated that the mechanical hyperalgesia in the tumor-bearing hind paw develops independently of sex, except that it developed a little sooner in female mice. A single intravenous injection of RvD1 (0.001-10 μg/kg) decreased hyperalgesia in both sexes with similar potency (ED50 = 0.0015 μg/kg) and efficacy. Repeated daily administration of 10 μg/kg RvD1 prolonged the analgesic effect and completely abolished hyperalgesia. This was also independent of sex.

CONCLUSION

In this preclinical mouse model of bone cancer pain, the development of pain and the analgesic effectiveness of RvD1 are not influenced by sex.

Chronic Musculoskeletal Pain and Central Sensitization-Related Symptoms in Chilean Victims of Political Violence During the 1973 to 1990 Dictatorship

People who suffer political violence (PV) are at risk of developing mental illness, chronic noncommunicable diseases, chronic pain, and decreased life expectancy. However, these indicators have been studied primarily in war veterans and refugees. The objective of this study was to estimate the prevalence of chronic musculoskeletal pain (CMP) and central sensitization-related symptoms (CSRS) in Chilean victims of PV during the 1973 to 1990 dictatorship. A cross-sectional observational multicenter study was conducted. Three hundred twenty-five people from six centers of a Ministry of Health of Chile program participated. The presence of CMP was determined by a history of pain ≥3 months, and CSRS was determined using the central sensitization inventory. About 69.23% of the sample had CMP (76.85% of females and 56.56% of males). About 60% of people with CMP showed a high level of CSRS severity (66.67% females and 44.93% males). Females presented significantly higher proportions of CMP (p < .001), and there was an association between CSRS severity and being female (p = .004). Chilean victims of PV during the 1973 to 1990 dictatorship presented a high prevalence of CMP and high-level CSRS severity. Both conditions affected females more than males. Future studies are needed to further delve into these variables' behavior and their influence on the quality of life in this population.

Licofelone, a Dual COX/LOX Inhibitor, Ameliorates Paclitaxel-Induced Mechanical Allodynia in Rats in a Cannabinoid Receptor-Dependent Manner

The use of paclitaxel as a chemotherapeutic drug is limited by the development of dose-dependent paclitaxel-induced neuropathic pain (PINP). Recently, we observed that the combination of indomethacin plus minocycline (IPM) attenuates PINP in a mouse model in a cannabinoid (CB) receptor-dependent manner. Indomethacin inhibits cyclooxygenase (COX) activity, and minocycline inhibits 5-lipoxygenase (5-LOX) activity. Male Sprague Dawley rats with paclitaxel-induced mechanical allodynia were treated with indomethacin, minocycline, IPM combination, licofelone (a dual COX/LOX inhibitor), or their vehicles. AM251, a CB1 receptor antagonist, and AM630, a CB2 receptor antagonist, were administered before the IPM combination or licofelone. Mechanical allodynia was measured using a dynamic plantar aesthesiometer. Molecular docking was performed using CB-Dock2. Licofelone and IPM combination had antiallodynic effects, which were significantly higher than either indomethacin or minocycline alone. AM251 and AM630 blocked the antiallodynic effects of IPM combination and licofelone. Molecular docking showed that licofelone binds to both CB1 and CB2 receptors with a high affinity similar to the phytocannabinoid 1-trans-delta-9-tetrahydrocannabinol and the synthetic cannabinoid WIN 55,212-2. Licofelone inhibits COX and LOX and/or directly interacts with CB receptors to produce antiallodynic effects in a rat model of PINP. The findings further suggest that licofelone could be a therapeutic agent for managing PINP.

Epigenomic landscape of the human dorsal root ganglion: sex differences and transcriptional regulation of nociceptive genes

Gene expression is influenced by chromatin architecture via controlled access of regulatory factors to DNA. To better understand gene regulation in the human dorsal root ganglion (hDRG) we used bulk and spatial transposase-accessible chromatin technology followed by sequencing (ATAC-seq). Using bulk ATAC-seq, we detected that in females diverse differentially accessible chromatin regions (DARs) mapped to the X chromosome and in males to autosomal genes. EGR1/3 and SP1/4 transcription factor binding motifs were abundant within DARs in females, and JUN, FOS and other AP-1 factors in males. To dissect the open chromatin profile in hDRG neurons, we used spatial ATAC-seq. The neuron cluster showed higher chromatin accessibility in GABAergic, glutamatergic, and interferon-related genes in females, and in Ca2+- signaling-related genes in males. Sex differences in transcription factor binding sites in neuron-proximal barcodes were consistent with the trends observed in bulk ATAC-seq data. We validated that EGR1 expression is biased to female hDRG compared to male. Strikingly, XIST, the long-noncoding RNA responsible for X inactivation, hybridization signal was found to be highly dispersed in the female neuronal but not non-neuronal nuclei suggesting weak X inactivation in female hDRG neurons. Our findings point to baseline epigenomic sex differences in the hDRG that likely underlie divergent transcriptional responses that determine mechanistic sex differences in pain.

Threat sensitivity in emotion dynamics: Negativity effects and sex differences

Evolutionary theorizing has given rise to the idea that responding to any particular threat may be more mandatory than responding to any particular reward. The present three experiments (total N = 375) sought to provide support for this perspective in an emotion dynamics task in which participants continuously rated their affective state in response to appetitive (reward-related) versus aversive (threat-related) images. Even when equating images for arousal and extremity, several negativity effects (e.g., steeper reactivity slopes in response to aversive images) were found. These negativity effects can serve as an experimental model of threat sensitivity, which should predispose some individuals, more than others, to symptoms related to fear and anxiety. This point was made with respect to sex differences, given that women (relative to men) are diagnosed with anxiety disorders at higher rates. Sex differences were pronounced and extensions of this work, both basic and applied, are proposed.

Sex differences in PD-L1-induced analgesia in paclitaxel-induced peripheral neuropathy mice depend on TRPV1-based inhibition of CGRP

AIMS

Paclitaxel (PTX) is extensively utilized in the management of diverse solid tumors, frequently resulting in paclitaxel-induced peripheral neuropathy (PIPN). The present study aimed to investigate sex differences in the behavioral manifestations and underlying pathogenesis of PIPN and search for clinically efficacious interventions.

METHODS

Male and female C57BL/6 mice (5-6 weeks and 12 months, weighing 18-30 g) were intraperitoneally (i.p.) administered paclitaxel diluted in saline (NaCl 0.9%) at a dose of 2 mg/kg every other day for a total of 4 injections. Von Frey and hot plate tests were performed before and after administration to confirm the successful establishment of the PIPN model and also to evaluate the pain of PIPN and the analgesic effect of PD-L1. On day 14 after PTX administration, PD-L1 protein (10 ng/pc) was injected into the PIPN via the intrathecal (i.t.) route. To knock down TRPV1 in the spinal cord, adeno-associated virus 9 (AAV9)-Trpv1-RNAi (5 μL, 1 × 1013 vg/mL) was slowly injected via the i.t. route. Four weeks after AAV9 delivery, the downregulation of TRPV1 expression was verified by immunofluorescence staining and Western blotting. The levels of PD-L1, TRPV1 and CGRP were measured via Western blotting, RT-PCR, and immunofluorescence staining. The levels of TNF-α and IL-1β were measured via RT-PCR.

RESULTS

TRPV1 and CGRP protein and mRNA levels were higher in the spinal cords of control female mice than in those of control male mice. PTX-induced nociceptive behaviors in female PIPN mice were greater than those in male PIPN mice, as indicated by increased expression of TRPV1 and CGRP. The analgesic effects of PD-L1 on mechanical hyperalgesia and thermal sensitivity were significantly greater in female mice than in male mice, with calculated relative therapeutic levels increasing by approximately 2.717-fold and 2.303-fold, respectively. PD-L1 and CGRP were partly co-localized with TRPV1 in the dorsal horn of the mouse spinal cord. The analgesic effect of PD-L1 in PIPN mice was observed to be mediated through the downregulation of TRPV1 and CGRP expression following AAV9-mediated spinal cord specific decreased TRPV1 expression.

CONCLUSIONS

PTX-induced nociceptive behaviors and the analgesic effect of PD-L1 in PIPN mice were sexually dimorphic, highlighting the significance of incorporating sex as a crucial biological factor in forthcoming mechanistic studies of PIPN and providing insights for potential sex-specific therapeutic approaches.

Role of HDAC5 Epigenetics in Chronic Craniofacial Neuropathic Pain

The information provided from the papers reviewed here about the role of epigenetics in chronic craniofacial neuropathic pain is critically important because epigenetic dysregulation during the development and maintenance of chronic neuropathic pain is not yet well characterized, particularly for craniofacial pain. We have noted that gene expression changes reported vary depending on the nerve injury model and the reported sample collection time point. At a truly chronic timepoint of 10 weeks in our model of chronic neuropathic pain, functional groupings of genes examined include those potentially contributing to anti-inflammation, nerve repair/regeneration, and nociception. Genes altered after treatment with the epigenetic modulator LMK235 are discussed. All of these differentials are key in working toward the development of diagnosis-targeted therapeutics and likely for the timing of when the treatment is provided. The emphasis on the relevance of time post-injury is reiterated here.

CGRP neuropeptide levels in patients with endometriosis-related pain treated with dienogest: a comparative study

BACKGROUND AND OBJECTIVE

Endometriosis (EM) involves the peripheral nervous system and causes chronic pain. Sensory nerves innervating endometriotic lesions contribute to chronic pain and influence the growth phenotype by releasing neurotrophic factors and interacting with nearby immune cells. Calcitonin gene-related peptide (CGRP), a pain-signaling neurotransmitter, has a significant role. This study examines the effect of Dienogest (DNG), a hormone therapy used for managing EM -related pain, on serum CGRP levels in EM patients.

MATERIALS AND METHODS

The Visual Analog Scale (VAS) assessed pain in diagnosed EM.

INDIVIDUALS

Serum samples were obtained to measure CGRP concentration. Participants received a 2 mg/day oral dose of DNG for six months as prescribed treatment. Additional serum samples were collected after this period to measure CGRP levels.

RESULTS

In the EM group, 6.7%, 33.3%, and 20% had ovarian EM, ovarian plus uterosacral, and ovarian plus bladder, respectively. The EM group showed higher CGRP serum levels than the control group (80.53 ± 16.13 vs. 58.55 ± 6.93, P < 0.0001). Still, after drug administration, CGRP serum levels significantly decreased compared to pre-treatment levels (69.66 ± 11.53 vs. 80.53 ± 16.13, P < 0.05). The EM group showed higher pain compared to the control group (7.93 ± 1.58 vs. 0.13 ± 0.35, P < 0.0001), but after drug administration, pain significantly decreased compared to pre-treatment levels (1.00 ± 2.00 vs. 7.93 ± 1.58, P < 0.05).

CONCLUSION

DNG administration reduces pain and serum CGRP levels in EM patients, offering the potential for innovative treatments and tailored options. Understanding neurotransmitter roles and drug effects can aid in discovering more effective modulators for these pathways.

Gender Differences in Pain Threshold, Unpleasantness, and Descending Pain Modulatory Activation Across the Adult Life Span: A Cross Sectional Study

The neurobiological underpinnings of gender differences in pain perception, and how these differences may be modified by age, are incompletely understood, placing patients at risk of suboptimal pain management. Using functional magnetic resonance imaging, we examined brain responses in the descending pain modulatory system (DPMS, specifically, dorsolateral prefrontal cortex, anterior cingulate cortex, insula, hypothalamus, amygdala, and periaqueductal gray, during an evoked pain task. We investigated the interaction of age and gender in our sample of healthy adults (27 females, 32 males, 30-86 years) on DPMS response. In a perceptually matched thermal pain paradigm, we investigated pain unpleasantness and neural responses for 3 heat pain percepts: just noticeable pain, weak pain, and moderate pain (MP). Females reported just noticeable pain at a lower temperature, but reported less unpleasantness at weak pain and MP percepts, compared to males. There was a significant age-by-gender interaction during moderate pain in the right anterior cingulate cortex and bilateral insula, such that, males had a stronger positive relationship between DPMS response and age compared to females in these regions. Our results indicate that differences in DPMS responses may explain some gender differences in pain perception and that this effect may change across the adult lifespan. PERSPECTIVE: Gender differences in pain have been well-documented but the brain mechanisms for these differences are still unclear. This article describes potential differences in brain functioning during different levels of pain that could explain differences in pain responses between men and women across the adult lifespan.

Assessing the association of coffee consumption on the relationship of chronic pain with depression and anxiety

BACKGROUND

A bidirectional relationship between chronic pain (CP) and mental disorders has been reported, and coffee was believed to be associated with both. However, the association of coffee in this bidirectional relationship remains unclear. We aim to analyze the association of coffee consumption on the relationship of CP with depression and anxiety.

METHODS

A total of 376,813 participants from UK Biobank were included. We collected data on anxiety, depression and CP from objects of our study population. The association of coffee consumption on the relationship of CP with depression and anxiety was assessed through logistic/linear regression models. Moreover, seemingly unrelated estimation test (SUEST) was used to compare whether the coefficients differed in two different groups.

RESULTS

We observed significant associations of coffee consumption in the interaction of CP with depression and anxiety, such as the association of multisite chronic pain (MCP) on self-reported depression (βcoffee = 0.421, βnon-coffee = 0.488, PSUEST = 0.001), and the association of MCP on generalized anxiety disorder-7 (GAD-7) scores (βcoffee = 0.561, βnon-coffee = 0.678, PSUEST = 0.004) were significantly different between coffee drinking and non-coffee drinking groups. Furthermore, in analysis stratified by gender, we found headache (βmale = 0.392, βfemale = 0.214, PSUEST = 0.022) and hip pain (βmale = 0.480, βfemale = 0.191, PSUEST = 0.021) had significant associations with self-reported depression between males and females groups in coffee drinkers.

CONCLUSIONS

Our results suggested that coffee consumption has a significant association on the relationship of CP with depression and anxiety.

Pleasantness and unpleasantness in somatosensory investigation

BACKGROUND

Qualitative sensory testing (QualST) is a simple, standardised, chairside method for evaluating somatosensory function; however, testing focuses on detection of cold, touch and pain with no recognition of perceptions of pleasantness and unpleasantness.

OBJECTIVES

The study aimed to utilise the stimuli in QualST, with the addition of a soft brush, to investigate stimulus-evoked perceptions of pleasantness and unpleasantness on the facial skin and if any side-to-side differences. Additional aims were to determine the inter- and intra-rater reliability using the modified QualST protocol and in the side-to-side differences.

METHODS

Thirty healthy adult female participants underwent three sessions of sensitivity testing as per the modified QualST protocol. Stimuli were applied bilaterally to the facial skin, and participants provided separate yes/no responses for presence of stimulus-evoked pleasantness, unpleasantness and/or differences between sides.

RESULTS

The stimuli were able to evoke sensations of pleasantness and unpleasantness with little differences in responses between the Q-tip and goat hair brush for the perceptions. Side-to-side differences in evoked perceptions were observed and greatest, when evaluating for pinprick-evoked unpleasantness (range between sessions = 18-19 participants). Acceptable percentage (≥90%) and excellent Cohen's Kappa (≥0.762) inter- and intra-rater agreements were identified for one or more positive responses for each stimulus modality and the targeted perception.

CONCLUSION

The modified QualST protocol provides a simple, reproducible method for the investigation of perceptions of pleasantness and unpleasantness, with readily accessible instrumentation to dental professionals and allowing for a more holistic approach in somatosensory testing.

Challenges with embedding an integrated sex and gender perspective into pain research: Recommendations and opportunities

The focus of this article, within this BBI horizons special issue, is on sex, gender, and pain. We summarise what is currently known about sex- and gender-related variations in pain, exploring intersectional biological and psychosocial mechanisms, and highlight gaps in knowledge and understanding. Five key challenges with the exploration of sex and gender in pain research are presented, relating to: conceptual imprecision, research bias, limitations with binary descriptions, integrating sex and gender, and timely adoption/implementation of good research practice. Guidance on how to overcome such challenges is provided. Despite clear evidence for sex and gender differences in pain, there are conceptual and methodological barriers to overcome. Innovation in methods and approach can help develop more effective and tailored treatment approaches for men, women, boys, girls, and gender-diverse people.

Sex-specific patterns of discomfort in patients with restless legs syndrome

STUDY OBJECTIVES

Sex differences in the prevalence of restless legs syndrome (RLS) have been reported, with a higher prevalence in women than in men. However, sex differences in clinical presentation remain unclear. We aimed to investigate the phenotypic differences in patients with RLS between sexes by comparing clinical presentations, iron status, polysomnographic parameters, and treatment.

METHODS

We retrospectively evaluated 614 patients (225 men, 389 women) diagnosed with RLS. To enhance the robustness of the study, an age-matched control group of 179 men and 286 women without sleep disorders was also included. Information on demographics and sleep-related questionnaires were collected. Iron status was evaluated using blood samples, and polysomnography was performed to evaluate periodic leg movements and comorbid sleep disorders.

RESULTS

Our analysis revealed no sex difference in the severity of RLS but a difference in the pattern of symptoms. Women had more frequent symptoms of pain and awakening during sleep, while men had more common motor symptoms (both self-reported symptoms and periodic leg movement on polysomnography). Women with RLS also had lower iron parameters and received more frequent iron supplementation therapy than men. In contrast to women with RLS, who presented higher sleep disturbances and depressive mood, men with RLS had a higher risk of comorbidities such as hypertension and cardiovascular disease. These sex differences were notably more pronounced than in the control group.

CONCLUSIONS

This study suggests that sex differences exist in RLS phenotypes, and clinicians should consider these differences for treatment.

CITATION

Kim J, Kim JR, Park HR, Joo EY. Sex-specific patterns of discomfort in patients with restless legs syndrome. J Clin Sleep Med. 2024;20(2):253-259.

Effects of somatostatin, a somatostatin agonist, and an antagonist, on a putative migraine trigger pathway

OBJECTIVE

To determine whether somatostatin (SST) could be a cortico-brainstem neurotransmitter involved in producing the headache of migraine.

BACKGROUND

There is evidence to support the idea that a cortico-brainstem-trigeminal nucleus neuraxis might be responsible for producing migraine headache; we have suggested that SST may be one of the neurotransmitters involved.

METHODS

Rats were anesthetised and prepared for recording neurons in either the periaqueductal gray matter (PAG) or nucleus raphe magnus (NRM), as well as the trigeminal nucleus caudalis (TNC). The dura mater and facial skin were stimulated electrically or mechanically. SST, the SST agonist L054264 and the SST antagonist CYN54806 were injected intravenously, by microinjection, or by iontophoresis into the PAG or NRM. Cortical neuronal activity was provoked by cortical spreading depression (CSD) or light flash (LF) and was monitored by recording cortical blood flow (CBF).

RESULTS

Intravenous injection of SST: (a) selectively decreased the responses of TNC neurons to stimulation of the dura, but not skin, for up to 5 h; (b) decreased the ongoing discharge rate of TNC neurons while simultaneously increasing the discharge rate of neurons in either brainstem nucleus and; (c) prevented, or reversed, the effect of CSD and LF on brainstem and trigeminal neuron discharge rates. CSD and LF decreased the discharge rate of neurons in both brainstem nuclei and increased the discharge rate of TNC neurons. These effects were reversed by L054264 and mimicked by CYN54806. Injections of L054264 into the PAG or NRM reduced the response of TNC neurons to dural stimulation and skin stimulation differentially, depending on the nucleus injected. Injections of CYN54806 into either brainstem nucleus potentiated the responses of TNC neurons to dural and skin stimulation, but without a marked differential effect.

CONCLUSIONS

These results imply that SST could be a neurotransmitter in a pathway responsible for migraine pain.

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.

Epigenetic HDAC5 Inhibitor Reverses Craniofacial Neuropathic Pain in Mice

Identifying and resolving molecular complexities underlying chronic neuropathic pain is a significant challenge. Among the numerous classes of histone deacetylases, Class I (HDAC 1-3) and Class III (sirtuins) have been best studied in experimental pain models where inhibitor pre-treatments but not post-treatments abrogate the development of pain-related behaviors. Post-treatment here in week 3 with less well-studied Class IIa HDAC4/5 selective inhibitor LMK235 diminishes the trigeminal ganglia increases of HDAC5 RNA and protein in two chronic orofacial neuropathic pain models to levels measured in naïve mice at week 10 post-model induction. HDAC4 RNA reported in lower limb inflammatory pain models is not evident in the trigeminal models. Many other gene alterations persisting at week 10 in the trigeminal ganglia (TG) are restored to naïve levels in mice treated with LMK235. Important pain-related upregulated genes Hoxc8,b9,d8; P2rx4, Cckbr, growth hormone (Gh), and schlafen (Slfn4) are greatly reduced in LMK235-treated mice. Fold increase in axon regeneration/repair genes Sostdc1, TTr, and Folr1 after injury are doubled by LMK235 treatment. LMK235 reduces the excitability of trigeminal ganglia neurons in culture isolated from nerve injured mice compared to vehicle-treated controls, with no effect on neurons from naïve mice. Electrophysiological characterization profile includes a shift where ∼20% of the small neurons recorded under LMK235-treated conditions are high threshold, whereas none of the neurons under control conditions have high thresholds. LMK235 reverses long-standing mechanical and cold hypersensitivity in chronic trigeminal neuropathic pain models in males and females (5,10 mg/kg), preventing development of anxiety- and depression-like behaviors. PERSPECTIVE: Data here support HDAC5 as key epigenetic factor in chronic trigeminal neuropathic pain persistence, validated with the study of RNA alterations, TG neuronal excitability, and pain-related behaviors. HDAC5 inhibitor given in week 3 restores RNA balance at 10 weeks, while upregulation remains for response to wound healing and chronic inflammation RNAs.

Spatial transcriptomics and single-nucleus RNA sequencing reveal a transcriptomic atlas of adult human spinal cord

Despite the recognized importance of the spinal cord in sensory processing, motor behaviors, and neural diseases, the underlying organization of neuronal clusters and their spatial location remain elusive. Recently, several studies have attempted to define the neuronal types and functional heterogeneity in the spinal cord using single-cell or single-nucleus RNA sequencing in animal models or developing humans. However, molecular evidence of cellular heterogeneity in the adult human spinal cord is limited. Here, we classified spinal cord neurons into 21 subclusters and determined their distribution from nine human donors using single-nucleus RNA sequencing and spatial transcriptomics. Moreover, we compared the human findings with previously published single-nucleus data of the adult mouse spinal cord, which revealed an overall similarity in the neuronal composition of the spinal cord between the two species while simultaneously highlighting some degree of heterogeneity. Additionally, we examined the sex differences in the spinal neuronal subclusters. Several genes, such as SCN10A and HCN1, showed sex differences in motor neurons. Finally, we classified human dorsal root ganglia (DRG) neurons using spatial transcriptomics and explored the putative interactions between DRG and spinal cord neuronal subclusters. In summary, these results illustrate the complexity and diversity of spinal neurons in humans and provide an important resource for future research to explore the molecular mechanisms underlying spinal cord physiology and diseases.

Crying the pain away: the nature, measurement, and function of benign masochism

This study explores benign masochism, the ostensibly non-adaptive enjoyment of inherently aversive experiences (e.g., rollercoasters). After confirming the proposed eight-factor structure of the Benign Masochism Scale (BMS), gender differences in BMS scores and their association with measures of acculturation were examined to assess if benign masochism reflects degree of immersion in the dominant culture. Data were then used to test the hypothesis that benign masochism serves an emotion regulatory function comparable to behaviors like substance use or non-suicidal self-injury. Participants (n = 585, 51.1% female) completed the BMS and measures of sensation-seeking, impulsivity, emotion regulation deficits, and acculturation. Finding suggest significant gender differences in benign masochism and links with degree of acculturation in participants from diverse backgrounds. Associations between BMS scores, impulsivity, sensation-seeking, and emotion regulation deficits were replicated here, though variables accounted for little variance in BMS scores. In spite of similarities to established clinical phenomena such as substance use and non-suicidal self-injury, the mechanisms underlying the common yet relatively understudied phenomenon of benign masochism appear to differ and require further exploration.

An aqueous Commiphora myrrha extract ameliorates paclitaxel-induced peripheral neuropathic pain in mice

Background: Chemotherapy-induced neuropathic pain (CINP) is a debilitating side effect in individuals undergoing cancer treatment. Treatment of CINP with the current available classes of drugs is limited and often yields unsatisfactory results. Finding therapeutic alternatives of plant origin could provide a new way for the management of CINP. Commiphora myrrha (CM) resin extract has been reported to have anti-inflammatory and analgesic activities, but the effect of CM on neuropathic pain is yet to be investigated in CINP. Objectives: The aim of this study was to investigate the antinociceptive effect of CM extract in a mouse model of paclitaxel-induced neuropathic pain (PINP). Methods: The effects of CM on thermal hyperalgesia and mechanical allodynia were assessed in female BALB/c mice with PINP using a hot plate and a plantar aesthesiometer, respectively. Motor coordination was evaluated using a rotarod apparatus. The involvement of transient receptor potential vanilloid channel 1 (TRPV1) in CM actions was investigated using a capsaicin (a TRPV1 agonist)-induced nociception test. The genetic expression of Trpv1, Nrf2, Sod2, and Hmox1 was assessed using real-time PCR, while protein expression of TRPV1, Iba-1, and CD11b was assessed using Wes™. Results: Administration of CM to mice with established PINP produced a dose-dependent reduction in thermal hyperalgesia. Prophylactic treatment of mice with CM prevented the development of paclitaxel-induced thermal hyperalgesia and mechanical allodynia. CM did not change the motor coordination of mice, as the reaction latency and the rotational velocity of animals pretreated with CM extract were similar to those of animals pretreated with vehicle. CM significantly decreased the number and duration of the flick responses following capsaicin injection into the dorsal surface of the hind paw of mice. The protein expression of TRPV1 was upregulated in the spinal cord of paclitaxel-treated animals compared to vehicle-only-treated control animals, while CM-treated animals had values similar to vehicle-only-treated control animals. The mRNA expression of Nrf2, a major antioxidant transcription factor, was upregulated in the paw skin of mice treated with CM compared to those treated with paclitaxel alone. Conclusion: These results indicate that CM may both treat established and prevent the development of paclitaxel-induced thermal hyperalgesia and mechanical allodynia without any impairment in the motor activity of mice. CM may mediate its action through the peripheral inhibition of TRPV1 channel activity, restoration of normal TRPV1 protein expression in the spinal cord, and elevation of cellular antioxidant defenses. CM has the potential to be used as a therapeutic alternative to treat CINP.

Gender-based differences in assessment and management of acute abdominal pain in the emergency department: A retrospective audit

BACKGROUND

Previous research has identified gender-based differences in acute pain management in the emergency department [ED]. The aim of this study was to compare pharmacological management of acute abdominal pain in the ED by gender.

METHODS

A retrospective chart audit was conducted at one private metropolitan ED including adult patients (18-80 years) who presented with acute abdominal pain in 2019. Exclusion criteria included: pregnancy, repeat presentation within the study period, pain-free at initial medical review or documented refusal of analgesia, and oligo-analgesia. Comparisons by gender included: (1) analgesia type and (2) time to analgesia. Bivariate analysis was undertaken using SPSS.

RESULTS

There were 192 participants: 61 (31.6 %) men and 131 (67.9 %) women. Men were more likely to get combined opioid and non-opioid medication as first line analgesia (men: 26.2 % n = 16; women: 14.5 % n = 19, p = .049). Median time from ED presentation to analgesia was 80 min for men (IQR: 60) versus 94 min for women (IQR: 58), (p = .119). Women (25.2 % n = 33) were more likely to receive their first analgesic after 90 min from ED presentation compared to men versus men (11.5 %, n = 7 p = .029). In addition, women waited longer before receiving second analgesia (women: 94, men: 30 min, p = .032).

CONCLUSION

Findings confirm there are differences in pharmacological management of acute abdominal pain in the ED. Larger studies are required to further explore differences observed in this study.

Clinical Phenomenology of Fibromyalgia Syndrome in Male Patients: Same But Different

The majority of knowledge about fibromyalgia syndrome (FMS) derives from studies of female patients. Little is known about the clinical characteristics and treatment outcomes of male patients with FMS. In this retrospective cohort study with a prospective posttreatment follow-up, we investigated whether male patients with FMS differ from female patients in terms of 1) symptom burden, 2) psychological characteristics, and 3) clinical treatment response. We identified 263 male (4%) out of 5,541 patients with FMS completing a 3-week multimodal pain-treatment program. Male patients (51.3 ± 9.1 years) were age- and time-matched (1:4) with female patients (N = 1,052, 51.3 ± 9.0 years). Data on clinical characteristics, psychological comorbidities, and treatment responses were obtained from medical records and validated questionnaires. Levels of perceived pain, psychological comorbidity, and functional capacity were similar between genders, although male patients with FMS showed a higher prevalence of alcohol abuse. Compared to female patients, male patients experienced themselves less often as overly accommodating (Cohen's d = -.42) but more often as self-sacrificing (d = .26) or intrusive (d = .23). Regarding pain coping, male patients were less likely to utilize mental distraction, rest- and relaxation techniques, or counteractive activities (d = .18-.27). Male patients showed a slightly worse overall response rate than women (69% vs 77%), although differences between individual outcome measures were small (d < .2). Although male and female patients in our cohort were similar in clinical presentation and treatment response, the gender-specific differences in interpersonal problems and pain coping suggest consideration of these aspects in the treatment of male patients with FMS. PERSPECTIVE: Knowledge about fibromyalgia mostly derives from studies of female patients. Identifying and understanding gender-specific differences in fibromyalgia is an important roadmap in the treatment of this syndrome by focusing on specific gender aspects such as differences in interpersonal problems and pain coping mechanisms.

Sex as a Biological Variable in Oral Diseases: Evidence and Future Prospects

The interest of the scientific community on sex and gender differences in health and disease has increased substantially over the past 25 to 30 y as a result of a long process of events and policies in the biomedical field. This is crucial as compelling evidence from human and animal model studies has demonstrated that sex and gender influence health, molecular and cellular processes, and response and predisposition to disease. The present scoping review aims to provide a synthesis of sex differences in oral diseases, ranging from periodontal disease to orofacial pain conditions, from risk of caries development to apical periodontitis. Overall, findings from this review further support a role for sexual dimorphism influencing disease predisposition and/or progression in oral diseases. Of note, this review also highlights the lack of consideration of additional factors such as gender and other psychosocial and external factors potentially influencing oral health and disease. New conceptual frameworks capable of capturing multiple fundamental domains and measurements should be developed in clinical and preclinical studies to inform sex-based individualized preventive and treatment strategies.

Sleep characteristics and pain in middle-aged and older adults: Sex-specific impact of physical and sitting activity

OBJECTIVES

The relationship between poor sleep health and worse pain is established. Physical activity has been successful in reducing chronic pain and improving sleep in aging adults. Despite known sex differences (more women than men experiencing chronic pain and insomnia), sex-specific patterns of interactive associations between physical activity, sleep, and pain remain unexplored. This study tested whether physical and sitting activity moderated associations between sleep characteristics and pain intensity, and whether sex further moderated these relationships.

METHODS

Participants aged 50+ (N = 170, Mage = 64.34, 72 women) completed an online survey measuring pre-sleep arousal (Pre-sleep Arousal Scale), sleep (Pittsburgh Sleep Quality Index), past month average pain intensity, and physical activity (International Physical Activity Questionnaire). Multiple regressions evaluated whether minutes of physical activity (total, vigorous, moderate, walking) or sitting activity, pre-sleep arousal, sleep, sex, or their interaction was associated with pain. Analyses controlled for education, difficulty walking, body mass index, total medical conditions, pain medication, and depressive/anxiety symptoms.

RESULTS

In women, vigorous activity interacted with total pre-sleep arousal and somatic pre-sleep arousal in its association with pain. Higher total arousal and somatic arousal were associated with worse pain intensity only for women who reported highest levels of vigorous activity. No such associations were observed for men or for other physical or sitting activity levels.

CONCLUSIONS

Vigorous physical activity may exacerbate the association between more pre-sleep arousal and worse pain in middle-aged and older women. Research should explore potential sex-specific mechanisms (e.g., inflammatory cytokines, arousal neural networks) underlying these results.

Drug Safety and Suicidality Risk of Chronic Pain Medications

Chronic pain is one of the main leading causes of disability in the world at present. A variety in the symptomatology, intensity and duration of this phenomenon has led to an ever-increasing demand of pharmacological treatment and relief. This demand for medication, ranging from well-known groups, such as antidepressants and benzodiazepines, to more novel drugs, was followed by a rise in safety concerns of such treatment options. The validity, frequency, and diversity of such concerns are discussed in this paper, as well as their possible effect on future prescription practices. A specific caution is provided towards the psychological safety and toll of these medications, regarding suicidality and suicidal ideation. Most significantly, this paper highlights the importance of pharmacovigilance and underscores the necessity of surveillance programs when considering chronic pain medication.

Chronic Cannabigerol as an Effective Therapeutic for Cisplatin-Induced Neuropathic Pain

Cannabigerol (CBG), derived from the cannabis plant, acts as an acute analgesic in a model of cisplatin-induced peripheral neuropathy (CIPN) in mice. There are no curative, long-lasting treatments for CIPN available to humans. We investigated the ability of chronic CBG to alleviate mechanical hypersensitivity due to CIPN in mice by measuring responses to 7 and 14 days of daily CBG. We found that CBG treatment (i.p.) for 7 and 14 consecutive days significantly reduced mechanical hypersensitivity in male and female mice with CIPN and reduced pain sensitivity up to 60-70% of baseline levels (p < 0.001 for all), 24 h after the last injection. Additionally, we found that daily treatment with CBG did not evoke tolerance and did not incur significant weight change or adverse events. The efficacy of CBG was independent of the estrous cycle phase. Therefore, chronic CBG administration can provide at least 24 h of antinociceptive effect in mice. These findings support the study of CBG as a long-lasting neuropathic pain therapy, which acts without tolerance in both males and females.

Functional neurological disorder is a feminist issue

Functional neurological disorder (FND) is a common and disabling disorder, often misunderstood by clinicians. Although viewed sceptically by some, FND is a diagnosis that can be made accurately, based on positive clinical signs, with clinical features that have remained stable for over 100 years. Despite some progress in the last decade, people with FND continue to suffer subtle and overt forms of discrimination by clinicians, researchers and the public. There is abundant evidence that disorders perceived as primarily affecting women are neglected in healthcare and medical research, and the course of FND mirrors this neglect. We outline the reasons why FND is a feminist issue, incorporating historical and contemporary clinical, research and social perspectives. We call for parity for FND in medical education, research and clinical service development so that people affected by FND can receive the care they need.

Has the COVID-19 outbreak altered the prevalence of low back pain among physiotherapy students?

OBJECTIVE

To evaluate the prevalence of low back pain (LBP) among physiotherapy students during the COVID-19 lockdown in the State of Israel.

PARTICIPANTS/METHODS

One hundred and sixty four physiotherapy students from all four-year student levels were invited to participate. One hundred and thirty-seven students (83.5%) were recruited in the study with 79 females (57.7%) and 58 males (42.3%). We used a structured anonymous questionnaire that sought standard information on age, height, weight, sports activity and low back pain (LBP) prevalence during three periods.

RESULTS

No significant differences were noted in the prevalence of LBP between the lockdown period compared to 12-month period in all four-year levels. More so, our findings showed that LBP prevalence among physiotherapy students was greater during the 12-month period compared to the lifetime period.

CONCLUSIONS

This study indicates that COVID-19 lockdown has no negative impact on the prevalence of LBP among physiotherapy students.

Cebranopadol for the Treatment of Chronic Pain

PURPOSE OF REVIEW

Regardless of the etiology, if pain persists chronically, it can detrimentally impact multiple aspects of a patient's well-being. Both physical and psychological effects are significant in many chronic pain patients. In this regard, psychological consequences can alter a patient's quality of life, functionality, and social functioning. Opioids have been the long-established gold standard for acute pain treatment in settings such as the postoperative period. An alternative to opioids in pain management has been highly sought after. Through a non-selective mechanism, cebranopadol is a first-in-class oral drug which combines agonism of the mu and nociceptin opioid peptide (NOP) receptors to provide improved analgesia, while reducing the occurrence of many typically opioid side effects. This manuscript is a narrative review of the possible use of cebranopadol in pain management.

RECENT FINDINGS

In pre-clinical studies, cebranopadol was similar to morphine in its pain control efficacy. In a phase IIa trial, cebranopadol was superior to placebo in reducing pain. In a randomized clinical trial, cebranopadol was superior to morphine. Another study concluded that cebranopadol had a lower misuse potential when compared to hydromorphone. In summary, cebranopadol offers new opportunities in treating chronic moderate to severe pain, while also countering risks of addiction. Additional studies are warranted to further evaluate the safety and efficacy of cebranopadol. In this regard, cebranopadol could prove to be a promising alternative to current pain treatment options.

Deep RNA-seq of male and female murine sensory neuron subtypes after nerve injury

ABSTRACT

Dorsal root ganglia (DRG) neurons have been well described for their role in driving both acute and chronic pain. Although nerve injury is known to cause transcriptional dysregulation, how this differs across neuronal subtypes and the impact of sex is unclear. Here, we study the deep transcriptional profiles of multiple murine DRG populations in early and late pain states while considering sex. We have exploited currently available transgenics to label numerous subpopulations for fluorescent-activated cell sorting and subsequent transcriptomic analysis. Using bulk tissue samples, we are able to circumvent the issues of low transcript coverage and drop-outs seen with single-cell data sets. This increases our power to detect novel and even subtle changes in gene expression within neuronal subtypes and discuss sexual dimorphism at the neuronal subtype level. We have curated this resource into an accessible database for other researchers ( https://livedataoxford.shinyapps.io/drg-directory/ ). We see both stereotyped and unique subtype signatures in injured states after nerve injury at both an early and late timepoint. Although all populations contribute to a general injury signature, subtype enrichment changes can also be seen. Within populations, there is not a strong intersection of sex and injury, but previously unknown sex differences in naïve states-particularly in Aβ-RA + Aδ-low threshold mechanoreceptors-still contribute to differences in injured neurons.

Catastrophizing and acceptance are mediators between insomnia and pain intensity-an SQRP study of more than 6,400 patients with non-malignant chronic pain conditions

Background

Sleep problems (insomnia) and chronic pain are associated. Chronic pain and insomnia/insufficient sleep quality share similar symptoms and features. Although they have a bidirectional relationship, more research is needed to understand how they interact via mediators and how moderators influence this relationship.

Aims

In this large clinical registry-based cohort study (N = 6,497), we investigate important mediators between insomnia and pain intensity in a cross-sectional sample of chronic pain patients using advanced path analysis. In addition, we investigate whether some background variables were moderators of the identified important paths or not and the correlation patterns between insomnia and pain intensity in relation to the mediators.

Methods

This study includes a cohort of adult patients with chronic non-cancer pain from the Swedish Quality Registry for Pain Rehabilitation (SQRP) with data on patient-reported outcome measures (PROMs) (2008-2016). The PROMs cover the background, pain aspects, psychological distress, pain-related cognitions, activity/participation, and health-related quality of life variables of the patients. Partial least squares structural equation modeling was used to explore the direct and indirect (via mediators) relationships between insomnia and pain intensity at baseline.

Results

In this cohort study, insomnia was prevalent at 62.3%, and both direct and indirect mediating paths were present for the insomnia-pain intensity relationship. All of the mediating effects combined were weaker than the direct effect between insomnia and pain intensity. The mediating effects via catastrophizing and acceptance showed the strongest and equal mediating paths, and mediating effects via fear avoidance were the second strongest. Insomnia showed stronger direct significant correlations with psychological distress, catastrophizing, and acceptance compared with those of pain intensity. Sex, age, education level, spatial extent of pain, or body mass index did not moderate the mediating paths.

Discussion and conclusion

This study confirms the existence of significant direct and mediating paths between reported insomnia and pain intensity. Future studies should focus on illuminating how sleep interventions influence pain intensity and other important key factors that contribute to the distress of chronic pain patients.

Unmasking the Adverse Impacts of Sex Bias on Science and Research Animal Welfare

Sex bias in biomedical and natural science research has been prevalent for decades. In many cases, the female estrous cycle was thought to be too complex an issue to model for, and it was thought to be simpler to only use males in studies. At times, particularly when studying efficacy and safety of new therapeutics, this sex bias has resulted in over- and under-medication with associated deleterious side effects in women. Many sex differences have been recognized that are unrelated to hormonal variation occurring during the estrous cycle. Sex bias also creates animal welfare challenges related to animal over-production and wastage, insufficient consideration of welfare (and scientific) impact related to differential housing of male vs female animals within research facilities, and a lack of understanding regarding differential requirements for pain recognition and alleviation in male versus female animals. Although many funding and government agencies require both sexes to be studied in biomedical research, many disparities remain in practice. This requires further enforcement of expectations by the Institutional Animal Care and Use Committee when reviewing protocols, research groups when writing grants, planning studies, and conducting research, and scientific journals and reviewers to ensure that sex bias policies are enforced.

Adapting psychedelic medicine for headache and chronic pain disorders

INTRODUCTION

While the majority of current research and development surrounds depression, demoralization, and substance use disorders, there are numerous reports of psychedelics having beneficial effects in other branches of medicine, including for headache disorders and chronic pain.

AREAS COVERED

This perspective reviews conventional forms of treatment for headache and other chronic pain disorders and describes historical, recent, and ongoing investigations of the therapeutic effects of psychedelics in these disorders. The first two clinical trials of psilocybin in headache disorders and recent case reports of psilocybin mushroom self-administration in chronic pain patients are described. This perspective highlights several factors related to the application of psychedelics in chronic pain disorders, comparing this with the standard psychedelic-assisted psychotherapy model of treatment.

EXPERT OPINION

When faced with a more constricted view of psychedelic medicine that features larger doses, underscores subjective effects in the mediation of therapeutic outcomes, and requires adjunctive psychotherapy to ensure safety and efficacy, the application of psychedelics in headache and chronic pain disorders may face challenges. It will be important to allow for flexibility and adaptation in protocols to evaluate different treatment paradigms, mechanisms of action, and the range of pharmacologic and extra-pharmacologic factors that affect psychedelic treatment outcomes.

Sex differences in thromboprophylaxis of the critically ill: a secondary analysis of a randomized trial

PURPOSE

Venous thromboembolism (VTE) is a common complication of critical illness. Sex- or gender-based analyses are rarely conducted and their effect on outcomes is unknown. We assessed for an effect modification of thromboprophylaxis (dalteparin or unfractionated heparin [UFH]) by sex on thrombotic (deep venous thrombosis [DVT], pulmonary embolism [PE], VTE) and mortality outcomes in a secondary analysis of the Prophylaxis for Thromboembolism in Critical Care Trial (PROTECT).

METHODS

We conducted unadjusted analyses using Cox proportional hazards analysis, stratified by centre and admission diagnostic category, including sex, treatment, and an interaction term. Additionally, we performed adjusted analyses and assessed the credibility of our findings.

RESULTS

Critically ill female (n = 1,614) and male (n = 2,113) participants experienced similar rates of DVT, proximal DVT, PE, any VTE, ICU death, and hospital death. In unadjusted analyses, we did not find significant differences in treatment effect favouring males (vs females) treated with dalteparin (vs UFH) for proximal leg DVT, any DVT, or any PE, but found a statistically significant effect (moderate certainty) favouring dalteparin in males for any VTE (males: hazard ratio [HR], 0.71; 95% confidence interval [CI], 0.52 to 0.96 vs females: HR, 1.16; 95% CI, 0.81 to 1.68; P = 0.04). This effect remained after adjustment for baseline characteristics (males: HR, 0.70; 95% CI, 0.52 to 0.96 vs females: HR, 1.17; 95% CI, 0.81 to 1.68; P = 0.04) and weight (males: HR, 0.70; 95% CI, 0.52 to 0.96 vs females: HR, 1.20; 95% CI, 0.83 to 1.73; P = 0.03). We did not identify a significant effect modification by sex on mortality.

CONCLUSIONS

We found an effect modification by sex of thromboprophylaxis on VTE in critically ill patients that requires confirmation. Our findings highlight the need for sex- and gender-based analyses in acute care research.

Connecting dots in disorders of gut-brain interaction: the interplay of stress and sex hormones in shaping visceral pain

Visceral pain and stress are tightly intertwined bodily and emotional phenomena, which enable a flexible adaptation to environmental challenges by activating a response repertoire to restore homeostasis along the gut-brain axis. However, visceral pain and stress can persist widely independent of the initial cause, acquiring independent disease values and posing major health burdens as predominant features in disorders of gut-brain interaction (DGBI). Epidemiological data consistently documents an increased prevalence for women to suffer from chronic visceral pain, possibly shaped by sex hormones and modulated by stress and its biological and psychosocial correlates. Yet, mechanisms underlying the complex interactions between altered visceroception, stress and sex remain widely elusive, especially in clinical populations with DGBI. We herein selectively review mechanisms of interactions between stress and sex in the complex pathophysiology of DGBI. A particular emphasis is laid on visceral pain, in which stress constitutes a major risk factor as well as mediator, and sex-related differences are particularly pronounced. Building on the neurobiology of stress and mechanisms of gut-brain interactions, we highlight putative target mechanisms via which visceral pain and stress may converge with sex effects into a triad. Accommodating a global demographic shift, we propose a lifespan perspective in future research, which may enable a more fine-tuned evaluation of this complex interplay exerting distinct challenges during vulnerable developmental phases. This viewpoint may advance our understanding of pathophysiological processes and can ultimately inspire novel tailored prevention strategies and therapeutic approaches in the treatment of chronic visceral pain and DGBI across the lifespan.

Program Evaluation: exploring health disparities that impact chronic pain referrals within a VA Health Care System

Introduction

The present Program Evaluation study examines sociodemographic characteristics of Veterans in the Phoenix VA Health Care System who have back pain, and specifically the likelihood of those characteristics being associated with a referral to the Chronic Pain Wellness Center (CPWC) in the year 2021. We examined the following characteristics: Race/ethnicity, gender, age, mental health diagnosis, substance use disorder diagnosis, and service-connected diagnosis.

Methods

Our study used cross sectional data from the Corporate Data Warehouse for 2021. 13624 records had complete data for the variables of interest. Univariate and multivariate logistic regression was used to determine the likelihood of patients' being referred to the Chronic Pain Wellness Center.

Results

The multivariate model found under-referral to be significant for younger adults and for patients who identified as Hispanic/Latinx, Black/African American, or Native American/Alaskan. Those with depressive disorders and opioid use disorders, on the other hand, were found to be more likely to be referred to the pain clinic. Other sociodemographic characteristics were not found to be significant.

Discussion

Study limitations include the use of cross-sectional data, which cannot determine causality, and the inclusion of patients only if the ICD-10 codes of interest were recorded for an encounter in 2021 (i.e., a prior history of a particular diagnosis was not captured). In future efforts, we plan to examine, implement, and track the impact of interventions designed to mitigate these identified disparities in access to chronic pain specialty care.

Effects of interdisciplinary pain rehabilitation programs on neuropathic and non-neuropathic chronic pain conditions - a registry-based cohort study from Swedish Quality Registry for Pain Rehabilitation (SQRP)

BACKGROUND AND AIM

Neuropathic pain arises as a direct consequence of a lesion or disease affecting the somatosensory system. Pharmacological treatments for neuropathic pain often fail despite following guidelines. Interdisciplinary Pain Rehabilitation Programs (IPRP) are an effective intervention for chronic pain conditions. Little research has investigated whether IPRP can benefit patients with chronic neuropathic pain compared to other chronic pain conditions. This study assesses the real-world effects of IPRP on patients with chronic neuropathic pain compared to non-neuropathic patients using Patient-Reported Outcome Measures (PROMs) available in the Swedish Quality Registry for Pain Rehabilitation (SQRP).

METHODS

A neuropathic group of patients (n = 1,654) were identified in two steps. This group was compared to a non-neuropathic group (n = 14,355) composed of common diagnoses (low back pain, fibromyalgia, whiplash associated disorders, and Ehlers-Danlos Syndrome) in relation to background variables, three overall outcome variables, and mandatory outcome variables (pain intensity, psychological distress symptoms, activity/participation aspects and health-related quality of life variables). Of these patients 43-44% participated in IPRP.

RESULTS

At assessment, the neuropathic group reported significantly (with small effect sizes (ES)) more physician visits the previous year, older age, shorter pain durations, and less spatial extent of the pain (moderate ES). Moreover, for the 22 mandatory outcome variables, we found only clinically insignificant differences according to ESs between the groups. For patients participating in IPRP, the neuropathic group displayed equal or in some cases slightly superior results compared to the non-neuropathic group.

DISCUSSION AND CONCLUSION

After assessing the real-world effects of IPRP, this large study found that neuropathic pain patients can benefit from the IPRP intervention. Both registry studies and RCTs are needed to better understand which patients with neuropathic pain are most suitable for IPRP and to what extent special considerations need to be made for these patients within the framework of IPRP.

Differences in chronic pain prevalence between men and women at mid-life: a systematic review protocol

INTRODUCTION

Epidemiological literature shows differences in chronic pain (CP) prevalence in men and women. Women are more likely to develop CP at different points of the life course, such as adolescence and old age. Less is known about the prevalence of CP by sex and the difference in prevalence during mid-life, when changes may predispose to an earlier differentiation in CP distribution. The aim of this study is to describe the difference in prevalence of CP at mid-life (ages 40-60) in men and women in the general population.

METHODS AND ANALYSIS

This systematic review follows Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Appropriate studies will be identified in the following databases: MEDLINE, EMBASE, AMED and PsycINFO. Two reviewers will independently screen each title and abstract. Studies eligible for data extraction will report estimates of CP prevalence for each sex, and/or a measure of the difference in prevalence between sexes. The findings will be reported in a narrative synthesis following the Social Research Council Methods Programme guidelines. A random effects meta-analysis will be conducted where the reviewers can justify combining results.

ETHICS AND DISSEMINATION

This review will summarise the prevalence of CP in men and women at mid-life, based on existing evidence. It is expected that the results will identify gaps in knowledge and areas for further research. The review will be submitted for publication in topic specific journals and disseminated to professional networks. Individual patient data are not included, so ethical approval is not required.

PROSPERO REGISTRATION NUMBER

CRD42021295895.

Prospective paired crossover evaluation of potential impact of investigator gender on perceived pain intensity early after acute or scheduled surgery

BACKGROUND

Postoperative pain is common but often difficult to assess, and there are many potential confounders. Over the last decades, the gender of investigator as well as participant has been found to influence pain perception in both preclinical and clinical studies. However, to our knowledge this has not been studied in various postoperative patients. Objectives of this study were to test the hypotheses that pain intensity levels early after acute or scheduled in- or out-hospital surgery are lower when evaluated by a female investigator, and higher when reported by a female patient.

METHODS

In this prospective observational paired crossover study, two investigators of opposite genders independently obtained individually reported pain intensity levels with a visual analogue scale in a mixed cohort of adult postoperative study patients at Skåne University Hospital in Malmö, Sweden.

RESULTS

In total, 245 (129 female) study patients were included and then one female excluded. The study patients rated their intensity of postoperative pain lower when evaluated by a female than by a male investigator (P = 0.006), where the male patients constituted the significant difference (P < 0.001). Pain intensity levels did not differ between female and male study patients (P = 0.210).

CONCLUSIONS

Main findings of lower pain intensity reported by males to a female than to a male investigator early after surgery in this paired crossover study in mixed postoperative patients, indicate that potential impact of investigator gender on pain perception should be considered and further evaluated in clinical bedside practice. Trial registration Retrospectively registered in the ClinicalTrials.gov research database on 24th June 2019 with TRN number NCT03968497.