Ethnic differences in cardiovascular-somatosensory interactions and in the central processing of noxious stimuli

Pain prevalence, intensity, and association with neuropsychiatric symptoms of dementia in immigrant and non-immigrant aged care residents in Australia

Pain recognition for culturally diverse people is complex as pain experience is subjective and influenced by cultural background. We compared the prevalence, intensity, and association of pain with neuropsychiatric symptoms (NPS) between immigrants and non-immigrants living with dementia in residential aged care homes (RACHs) who were referred to two Dementia Support Australia programs. Immigrant status was defined by the documented country of birth. Pain and NPS were assessed using PainChek® and the Neuropsychiatric Inventory, respectively. Subgroup analyses were also completed for English-speaking and non-English-speaking immigrants. A total of 17,637 referrals [immigrants, n = 6340; non-immigrants, n = 11,297] from 2792 RACHs were included. There were no significant differences for the prevalence of pain across all groups. Immigrants were slightly more likely to have moderate pain or severe pain than non-immigrants. Non-English-speaking immigrants had 0.5 points higher total pain scores on average (Cohen's d = 0.10 [0.05, 0.15], p < 0.001) than non-immigrants. Total pain score had a significant effect on total NPS severity scores in all groups. While pain prevalence is similar across groups, higher pain intensities are more common among immigrants living with dementia. Increased care staff awareness, education, and training about the potential effect of culture on pain expression is needed.

Association between the Number of Days/Week of Different Levels of Physical Activity and Chronic Pain in People of Different Races: A Mendelian Randomization Study

OBJECTIVE

Regular physical activity is beneficial for health, but the effect of the number of days/week of physical activity on chronic pain (CP) remains unclear, so we used a two-sample Mendelian randomization (MR) analysis to explore the relationship between the number of days/weeks of different levels of physical activity and chronic pain in people of different races.

METHODS

We obtained summary data from genome-wide association studies (GWASs) on the number of days/week of physical activity and multisite chronic pain in European, South Asian, East Asian, Middle Eastern, and African American populations. The single-nucleotide polymorphisms (SNPs) of the exposed data were visualized with a Manhattan plot via the R program. MR analysis was performed by the MR-Base platform.

RESULTS

The results indicated that a higher number of days/week with ≥10 min of walking protects against CP in African American and Afro-Caribbean populations (inverse-variance weighting, IVW p < 0.05) but has little effect on people of different races (IVW p > 0.05). A higher number of days/week with ≥10 min of moderate physical activity increased the risk of CP in European and South Asia (IVW p < 0.05) but had little effect on people of different races (IVW p > 0.05). The number of days/week of ≥10 min of vigorous physical activity increased the risk of CP in Europeans (IVW p < 0.05) and protected against CP in African Americans and Afro-Caribbeans (IVW p < 0.05).

CONCLUSIONS

A higher number of days/week of moderate and vigorous physical activity increased the risk of CP in Europeans; however, a higher number of days/week of walking and vigorous physical activity may protect against CP in African American and Afro-Caribbean individuals.

Addressing chronic pain disparities between Black and White people: a narrative review of socio-ecological determinants

A 2019 review article modified the socio-ecological model to contextualize pain disparities among different ethnoracial groups; however, the broad scope of this 2019 review necessitates deeper socio-ecological inspection of pain within each ethnoracial group. In this narrative review, we expanded upon this 2019 article by adopting inclusion criteria that would capture a more nuanced spectrum of socio-ecological findings on chronic pain within the Black community. Our search yielded a large, rich body of literature composed of 174 articles that shed further socio-ecological light on how chronic pain within the Black community is influenced by implicit bias among providers, psychological and physical comorbidities, experiences of societal and institutional racism and biomedical distrust, and the interplay among these factors. Moving forward, research and public-policy development must carefully take into account these socio-ecological factors before scaling up pre-existing solutions with questionable benefit for the chronic pain needs of Black individuals.

The Relationship Between Experienced Discrimination and Pronociceptive Processes in Native Americans: Results From the Oklahoma Study of Native American Pain Risk

Native Americans (NAs) have higher pain rates than the general U.S. population. It has been found that increased central sensitization and reduced pain inhibition are pronociceptive processes that increase pain risk; yet, little attention has focused on the influence of psychosocial factors. Discrimination is a psychosocial factor associated with increased pain in other minoritized groups; however, it is unclear whether it also promotes pain in NAs. This study analyzed data from 269 healthy, pain-free participants (N = 134 non-Hispanic whites [NHWs], N = 135 NAs) from the Oklahoma Study of Native American Pain Risk. Experienced discrimination was measured using the Everyday Discrimination Scale (EDS). Nociceptive processes were measured via static measures of spinal sensitivity (nociceptive flexion reflex [NFR] threshold, 3-stimulation NFR threshold), temporal summation of pain (TS-Pain) and nociceptive flexion reflex (TS-NFR), and conditioned pain modulation of pain (CPM-Pain) and NFR (CPM-NFR). Results demonstrated that greater discrimination was associated with enhanced TS-NFR and impaired CPM-NFR but not static measures of spinal sensitivity or measures of pain modulation (TS-Pain, CPM-Pain). Although the effects of discrimination on outcomes were similar in both groups (not moderated by ethnicity), NAs experienced higher levels of discrimination and therefore discrimination mediated a relationship between ethnicity and impaired CPM-NFR. This indicates experienced discrimination may promote a pain risk phenotype in NAs that involves spinal sensitization resulting from impaired inhibition of spinal nociception without sensitization of pain experience. PERSPECTIVE: This study found that discrimination was associated with spinal sensitization and impaired descending inhibition of spinal nociception. These findings bolster our understanding of how social stressors experienced disproportionately by minoritized groups can contribute to pain outcomes.

Psychosocial and cardiometabolic predictors of chronic pain onset in Native Americans: serial mediation analyses of 2-year prospective data from the Oklahoma Study of Native American Pain Risk

ABSTRACT

Chronic pain results in considerable suffering, as well as significant economic and societal costs. Previous evidence suggests that Native Americans (NAs) have higher rates of chronic pain than other U.S. racial or ethnic groups, but the mechanisms contributing to this pain disparity are poorly understood. The Oklahoma Study of Native American Pain Risk was developed to address this issue and recruited healthy, pain-free NAs and non-Hispanic Whites. Cross-sectional analyses identified several measures of adversity (eg, trauma and discrimination), cognitive-affective factors (perceived stress and pain-related anxiety/catastrophizing), and cardiometabolic factors (eg, body mass index, blood pressure, and heart rate variability) that were associated with pronociceptive processes (eg, central sensitization, descending inhibition, and hyperalgesia). Every 6-months after enrollment, eligible participants (N = 277) were recontacted and assessed for the onset of chronic pain. This study examines predictors of chronic pain onset in the 222 participants (80%) who responded over the first 2 years. The results show that NAs developed chronic pain at a higher rate than non-Hispanic Whites (OR = 2.902, P < 0.05), even after controlling for age, sex, income, and education. Moreover, serial mediation models identified several potential pathways to chronic pain onset within the NA group. These paths included perceived discrimination, psychological stress, pain-related anxiety, a composite measure of cardiometabolic risk, and impaired descending inhibition of spinal nociception (assessed from conditioned pain modulation of the nociceptive flexion reflex). These results provide the first prospective evidence for a pain disparity in NAs that seems to be promoted by psychosocial, cardiometabolic, and pronociceptive mechanisms.

Dysmenorrhea and associated symptoms in Ethiopia: A systematic review and meta-analysis

Introduction:

Dysmenorrhea is the most common gynecologic compliant and reproductive health problem among adolescents, young, and reproductive age group. Dysmenorrhea has psychological, physical, and behavioral impact on adolescent girls in different regions.

Objective:

This systematic review and meta-analysis aimed to assess the overall prevalence of dysmenorrhea, its pain intensity and associated symptoms in Ethiopia and compare with other countries.

Methods:

Literatures from PubMed, MEDLINE, EMABSE, CINHAL, SCOPUS, Hinari, Africa journals, and Google scholar were retrieved. Eligible cross-sectional studies were included for meta-analysis. I2 statistics was calculated to check heterogeneity. Subgroup analysis based on outcome of interest was performed. Sensitivity analysis was undertaken to examine the level of heterogeneity.

Results:

The prevalence of overall and primary dysmenorrhea in Ethiopia was 72% (95%CI 68–77) and 72.27% (95%CI 69.8–75.33) respectively. Back pain 56.62% (95%CI 46.68–66.57) and fatigue 51.51% (95%CI 40.08–62.94) were more common than headache 29.15% (95%CI 18.16–40.14) whereas moderate pain 41.03% (95%CI 33.98–48.07) was more common than mild 31.83% (95%CI 21.61–42.05) and severe pain intensity 21.57% (95%CI 14.24–28.89). The prevalence between small and large samples, Northern and South/West Ethiopia, and school girls and university students were nearly similar. Positive family history (OR = 4.05; 95%CI 3.15–5.20), early menarche (OR = 2.91; 95%CI 2.00–4.24) and irregular monthly menstrual cycle (OR = 1.87, 95%CI 1.23–2.84) were the predictors of dysmenorrhea.

Conclusion:

Compared with other countries, the prevalence of dysmenorrhea in Ethiopia is moderate, presenting as mainly back pain and fatigue with moderate pain intensity. Positive family history, early menarche, and irregular menstrual cycle are the positive contributing factors.

Invariance of the PAINAD Scale Between the Black and White Residents Living With Dementia

The purpose of this study was to test the reliability and validity of the Pain Assessment in Advanced Dementia (PAINAD) and particularly consider whether or not this measure was invariant when used among the Black and White residents. Baseline data from an implementation study testing that included a sample of 553 residents, 30% of who were Black, from 55 nursing were included in this study. The Winsteps statistical program was used to perform the Rasch analysis and evaluate the reliability and validity of the measure based on internal consistency, infit and outfit statistics, mapping, and a differential item functioning (DIF) analysis. The AMOS statistical program was used for confirmatory factor analysis. The findings supported the reliability and validity of the PAINAD when used with these individuals and demonstrated that there was no evidence of invariance between the Black and White residents. All the items fit the model, but there was not a good spread of the items across the pain level of the participants. The majority of the participants (75%) were so low in pain signs or symptoms that they could not be differentiated. Based on the clinical practice and observations, it is recommended that additional items can be added to the measure such as observing the individual for evidence of resisting care, retropulsion when trying to stand, hitting or kicking when turning in bed, hitting or kicking when transferring from bed to chair, hitting or kicking when ambulating, or hitting or kicking when raising arms, less engagement with others, and decreased participation in the activities previously enjoyed.

Effects of Mindfulness-Based Stress Reduction on Experimental Pain Sensitivity and Cortisol Responses in Women With Early Life Abuse: A Randomized Controlled Trial

OBJECTIVE

Early life abuse (ELAb) initiates pathophysiological cascades resulting in long-term maladaptive stress responsivity, hyperalgesia, and an increased risk of psychopathology. Mindfulness-based stress reduction (MBSR) is effective in modifying psychological and somatic symptoms; thus, we predicted that MBSR would be particularly efficacious for women with ELAb.

METHOD

Medically healthy women (mean age = 31 years) with or without a history of early (≤13 years) physical or sexual abuse provided self-report measures and were tested in the laboratory before and after randomization to standard MBSR (n = 52) or social support (SSG) (n = 60) for 8 weeks. The laboratory procedure involved pain testing using the cold pressor and temporal summation of heat pain (indexing central sensitization) procedures, and exposure to the Trier Social Stress Test. Plasma cortisol in response to the experimental protocol was assessed as area under the curve (AUC).

RESULTS

The interventions differentially impacted pain sensitivity and cortisol AUC for women with ELAb, as MBSR increased the temporal summation of heat pain intensity ratings (p = .024) and reduced cortisol AUC (p = .004). For women without ELAb, MBSR decreased cold pressor tolerance (p = .045) and decreased the temporal summation of heat pain intensity ratings relative to SSG (p = .024). Both MBSR and SSG improved depression symptoms and emotion regulation abilities (p values < .001); however, MBSR was associated with greater benefits in describing emotions (p = .008) and impulse control (p = .017) for women with ELAb.

CONCLUSIONS

Women with ELAb benefited from MBSR-specific improvements in central sensitization, mindfulness skills, and emotion regulation abilities. This is the first study to examine the efficacy of MBSR in modifying affective and somatic symptoms based on ELAb status and provides evidence for considering ELAb in tailoring treatment approaches.Trial Registration: ClinicalTrials.gov Identifier: NCT01995916; https://clinicaltrials.gov/ct2/show/NCT01995916.

Greater mechanical temporal summation of pain in Latinx-Americans and the role of adverse life experiences

Supplemental Digital Content is Available in the Text.

Latinx-Americans showed greater temporal summation, adversity, and adversity correlates relative to non-Hispanic Whites. Discrimination and lifespan social status change inversely related to summation for Latinx-Americans.

Introduction:

Adverse life experiences disproportionately impact Latinx-Americans and are related to greater chronic pain rates. However, little is known about how adversities interact with central pain mechanisms for the development of later pain among Latinx-Americans.

Objectives:

The current study examined the relationship between adverse life experiences (eg, trauma and ethnic discrimination) and correlates (eg, social status) with mechanical temporal summation of pain (a proxy measure of central sensitization) between pain-free U.S. native Latinx (n = 65) and non-Hispanic White (NHW) (n = 51) adults.

Methods:

Participants completed self-report adverse life experience and correlational measures regarding childhood and adulthood and a mechanical temporal summation protocol.

Results:

Relative to NHWs, Latinx-Americans reported experiencing significantly greater trauma, discrimination, and lower social status during childhood and adulthood, along with greater temporal summation. Contrary to hypotheses, recent and lifetime experiences of ethnic discrimination significantly correlated with less temporal summation among Latinx-Americans. Decreases in objective and subjective social status across the lifespan (childhood to present day) correlated with greater temporal summation for Latinx-Americans. However, r-to-z transformation analyses confirmed that significant adversity and social status correlations observed among the Latinx group did not significantly differ from NHW participants.

Conclusions:

The present findings highlight the complex association between adverse experiences, adverse experience risk factors, and pain for Latinx-Americans. Given the disproportion of experienced pain and adversity among Latinx-Americans, the current findings suggest that a better understanding of the unique adversities for this sample may help elucidate the mechanisms underlying the relationship between adversities, adversity correlates, and pain risk for Latinx-Americans.

Assessing peripheral fibers, pain sensitivity, central sensitization, and descending inhibition in Native Americans: main findings from the Oklahoma Study of Native American Pain Risk

Native Americans (NAs) have a higher prevalence of chronic pain than other U.S. racial/ethnic groups, but there have been few attempts to understand the mechanisms of this pain disparity. This study used a comprehensive battery of laboratory tasks to assess peripheral fiber function (cool/warm detection thresholds), pain sensitivity (eg, thresholds/tolerances), central sensitization (eg, temporal summation), and pain inhibition (conditioned pain modulation) in healthy, pain-free adults (N = 155 NAs, N = 150 non-Hispanic Whites [NHWs]). Multiple pain stimulus modalities were used (eg, cold, heat, pressure, ischemic, and electric), and subjective (eg, pain ratings and pain tolerance) and physiological (eg, nociceptive flexion reflex) outcomes were measured. There were no group differences on any measure, except that NAs had lower cold-pressor pain thresholds and tolerances, indicating greater pain sensitivity than NHWs. These findings suggest that there are no group differences between healthy NAs and NHWs on peripheral fiber function, central sensitization, or central pain inhibition, but NAs may have greater sensitivity to cold pain. Future studies are needed to examine potential within-group factors that might contribute to NA pain risk.

Pain-related anxiety promotes pronociceptive processes in Native Americans: bootstrapped mediation analyses from the Oklahoma Study of Native American Pain Risk

INTRODUCTION

Evidence suggests Native Americans (NAs) experience higher rates of chronic pain than the general US population, but the mechanisms contributing to this disparity are poorly understood. Recently, we conducted a study of healthy, pain-free NAs (n = 155), and non-Hispanic whites (NHWs, n = 150) to address this issue and found little evidence that NAs and NHWs differ in pain processing (assessed from multiple quantitative sensory tests). However, NAs reported higher levels of pain-related anxiety during many of the tasks.

OBJECTIVE

The current study is a secondary analysis of those data to examine whether pain-related anxiety could promote pronociceptive processes in NAs to put them at chronic pain risk.

METHODS

Bootstrapped indirect effect tests were conducted to examine whether pain-related anxiety mediated the relationships between race (NHW vs NA) and measures of pain tolerance (electric, heat, ischemia, and cold pressor), temporal summation of pain and the nociceptive flexion reflex (NFR), and conditioned pain modulation of pain/NFR.

RESULTS

Pain-related anxiety mediated the relationships between NA race and pain tolerance and conditioned pain modulation of NFR. Exploratory analyses failed to show that race moderated relationships between pain-related anxiety and pain outcomes.

CONCLUSION

These findings imply that pain-related anxiety is not a unique mechanism of pain risk for NAs, but that the greater tendency to experience pain-related anxiety by NAs impairs their ability to engage descending inhibition of spinal nociception and decreases their pain tolerance (more so than NHWs). Thus, pain-related anxiety may promote pronociceptive processes in NAs to place them at risk for future chronic pain.

Can aberrant spinal nociception be a marker of chronicity of pain in fibromyalgia syndrome?

Pain sensitivity is a recognized feature of fibromyalgia syndrome (FMS) but the contribution of spinal nociceptive circuitry to this phenomenon is unknown. Therefore, the objectives were to study the changes in spinal nociception i.e. nociceptive flexion reflex (NFR) in patients with FMS and to investigate correlation if any, between NFR threshold, pain duration and tender points in FMS. One hundred and three patients with FMS and 74 healthy volunteers participated in the study. To record NFR, sural nerve was stimulated in the retro malleolar region and the reflex response was recorded from the short head of biceps femoris muscle. NFR was elicited at significantly lower [21.0(18.0-25.0)V] thresholds in FMS group when compared to healthy subjects [30.0(24.75-35.0)V; p = 0.001] indicating hyperalgesic response to electrocutaneous stimulation in FMS patients. The latency and other parameters of NFR were comparable in both the groups. No significant correlation was found among NFR threshold and pain duration or tender points. On the basis of results of present study, it may be concluded that the functional deficit of the spinal nociceptive system can contribute to hyperalgesia in FMS. This is first study that correlates a marker of central hyper-excitability (NFR threshold) with clinical symptoms (pain duration and tender points) of FMS.

Racial/ethnic differences in experimental pain sensitivity and associated factors - Cardiovascular responsiveness and psychological status

This study evaluated the contributions of psychological status and cardiovascular responsiveness to racial/ethnic differences in experimental pain sensitivity. The baseline measures of 3,159 healthy individuals-non-Hispanic white (NHW): 1,637, African-American (AA): 1,012, Asian: 299, and Hispanic: 211-from the OPPERA prospective cohort study were used. Cardiovascular responsiveness measures and psychological status were included in structural equation modeling based mediation analyses. Pain catastrophizing was a significant mediator for the associations between race/ethnicity and heat pain tolerance, heat pain ratings, heat pain aftersensations, mechanical cutaneous pain ratings and aftersensations, and mechanical cutaneous pain temporal summation for both Asians and AAs compared to NHWs. HR/MAP index showed a significant inconsistent (mitigating) mediating effect on the association between race/ethnicity (AAs vs. NHWs) and heat pain tolerance. Similarly, coping inconsistently mediated the association between race/ethnicity and mechanical cutaneous pain temporal summation in both AAs and Asians, compared to NHWs. The factor encompassing depression, anxiety, and stress was a significant mediator for the associations between race/ethnicity (Asians vs. NHWs) and heat pain aftersensations. Thus, while pain catastrophizing mediated racial/ethnic differences in many of the QST measures, the psychological and cardiovascular mediators were distinctly restrictive, signifying multiple independent mechanisms in racial/ethnic differences in pain.

Analgesic potential of PF-06372865, an α2/α3/α5 subtype-selective GABAA partial agonist, in humans

BACKGROUND

This study investigated the analgesic effects of two doses (15 and 65 mg) of PF-06372865, a novel α2/α3/α5 gamma-aminobutyric acid A (GABA_A) subunit selective partial positive allosteric modulator (PAM), compared with placebo and pregabalin (300 mg) as a positive control.

METHODS

We performed a randomised placebo-controlled crossover study (NCT02238717) in 20 healthy subjects, using a battery of pain tasks (electrical, pressure, heat, cold and inflammatory pain, including a paradigm of conditioned pain modulation). Pharmacodynamic measurements were performed at baseline and up to 10 h after dose.

RESULTS

A dose of 15 mg PF-06372865 increased pain tolerance thresholds (PTTs) for pressure pain at a ratio of 1.11 (90% confidence interval [CI]: 1.02, 1.22) compared with placebo. A dose of 65 mg PF-06372865 led to an increase in PTT for the cold pressor at a ratio of 1.17 (90% CI: 1.03, 1.32), and pressure pain task: 1.11 (90% CI: 1.01, 1.21). Pregabalin showed an increase in PTT for pressure pain at a ratio of 1.15 (95% CI: 1.06, 1.26) and cold pressor task: 1.31 (90% CI: 1.16, 1.48).

CONCLUSION

We conclude that PF-06372865 has analgesic potential at doses that do not induce significant sedation or other intolerable adverse events limiting its clinical use. In addition, the present study established the potential role for this battery of pain tasks as a tool in the development of analgesics with a novel mechanism of action, for the treatment of various pain states including neuropathic pain and to establish proof-of-concept.

CLINICAL TRIALS REGISTRATION

NCT0223871.

Ethnicity, Cortisol, and Experimental Pain Responses Among Persons With Symptomatic Knee Osteoarthritis

OBJECTIVES

Although several factors are known to contribute to ethnic differences in pain, relatively little attention has been devoted to physiological factors. Our first aim was to examine the relationship between cortisol and pain responses during a cold-pressor task (CPT) among African American (AA) and non-Hispanic White (NHW) adults with knee osteoarthritis (OA). Our second aim was to assess the relationship between perceived racial discrimination and cortisol among AA participants.

MATERIALS AND METHODS

Participants were 91 (56 AA; 35 NHW) community-dwelling adults between the ages of 45 to 85 with knee OA based upon the American College of Rheumatology clinical criteria. Plasma cortisol was measured at 3 timepoints: (1) baseline, (2) before the CPT, and (3) 20 minutes following the CPT. Perceived racial discrimination was measured by the Experiences of Discrimination scale.

RESULTS

Using linear regression, we found a significant interaction between ethnicity and cortisol before the CPT with pain intensity ratings (β=-0.26; P=0.02). Analysis of simple slopes revealed that cortisol concentrations were negatively associated with pain intensity ratings in NHW participants (β=-0.54; P=0.001), but not in AA participants (β=-0.15; P=0.26). Perceived racial discrimination was not related to cortisol concentrations or pain ratings.

DISCUSSION

Consistent with previous findings in young healthy adults, cold-pressor pain responses are related to pre-CPT cortisol concentrations in NHW persons with knee OA but not in their AA counterparts. Additional studies are required to better understand this finding.

Different pain responses to chronic and acute pain in various ethnic/racial groups

AIM

Our goal in this study was to review the similarities and differences among ethnic groups and their respective responses to acute and chronic clinically related and experimentally induced pain.

METHOD

In this review, the PUBMED and Google-Scholar databases were searched to analyze articles that have assessed the variations in both acute and chronic pain responses among different ethnic/racial groups.

RESULTS

According to the results from 42 reviewed articles, significant differences exist among ethnic-racial groups for pain prevalence as well as responses to acute and chronic pain. Compared with Caucasians, other ethnic groups are more susceptible to acute pain responses to nociceptive stimulation and to the development of long-term chronic pain.

CONCLUSION

These differences need to be addressed and assessed more extensively in the future in order to minimize the pain management disparities among various ethnic-racial groups and also to improve the relationship between pain management providers and their patients.

Ethnic Differences in the Effects of Naloxone on Sustained Evoked Pain: A Preliminary Study

Ethnic differences in pain response have been well documented, with non-Hispanic Black (NHB) participants reporting enhanced clinical pain and greater laboratory-evoked pain sensitivity to a variety of quantitative sensory testing (QST) methods compared to non-Hispanic Whites (NHW). One potential mechanism that may contribute to these disparities is differential functioning of endogenous pain-regulatory systems. To evaluate endogenous opioid (EO) mechanisms in pain responses, we examined group differences in response to tonic capsaicin pain following double-blinded crossover administration of saline and the opioid antagonist, naloxone. Ten percent topical capsaicin cream and a thermode were applied to the dorsum of the non-dominant hand, maintaining a constant temperature of 40°C for 90 min. Naloxone (0.1 mg/kg) or saline placebo was administered at the 25 min mark and post-drug pain intensity ratings were obtained every 5 min thereafter. As an index of EO function, blockade effects were derived for each participant, reflecting the difference between mean post-drug pain intensity ratings under the saline versus naloxone conditions, with higher positive scores reflecting greater EO inhibition of pain. Thirty-nine healthy, young individuals (19 non-Hispanic Black [NHB], 20 non-Hispanic White [NHW]) participated. Group difference in EO function were identified, with NHB participants displaying lower EO function scores (mean=-10.8, SD=10.1) as compared to NHW participants (mean=-0.89, SD=11.5; p=0.038). NHB participants experienced significant paradoxical analgesia with naloxone. Thirty five percent of the NHW participants showed a positive blockade effect indicating EO analgesia (i.e., an increase in pain with naloxone), while only 10% of the NHB participants exhibited evidence of EO analgesia. These findings suggest differential functioning of the endogenous opioid pain regulatory system between NHB and NHW participants. Future research is warranted to examine whether these differences contribute to the disparities observed in clinical pain between groups.

Demographic Predictors of Pain Sensitivity: Results From the OPPERA Study

The demographic factors of sex, age, and race/ethnicity are well recognized as relevant to pain sensitivity and clinical pain expression. Of these, sex differences have been the most frequently studied, and most of the literature describes greater pain sensitivity for women. The other 2 factors have been less frequently evaluated, and current literature is not definitive. Taking advantage of the large Orofacial Pain: Prospective Evaluation and Risk Assessment (OPPERA) study cohort, we evaluated the association of sex, age, and self-reported race with 34 measures of pressure, mechanical, and thermal pain sensitivity encompassing threshold and suprathreshold perception. Women were significantly more pain-sensitive than men for 29 of 34 measures. Age effects were small, and only significant for 7 of 34 measures, however, the age range was limited (18-44 years of age). Race/ethnicity differences varied across groups and pain assessment type. Non-Hispanic white individuals were less pain-sensitive than African-American (for 21 of 34 measures), Hispanic (19 of 34), and Asian (6 of 34) individuals. No pain threshold measure showed significant racial differences, whereas several suprathreshold pain measures did. This suggests that racial differences are not related to tissue characteristics or inherent nociceptor sensitivity. Rather, the differences observed for suprathreshold pain ratings or tolerance are more likely related to differences in central nociceptive processing, including modulation imposed by cognitive, psychological, and/or affective factors.

PERSPECTIVE

The influence of sex, age, and race/ethnicity on various aspects of pain sensitivity, encompassing threshold and suprathreshold measures and multiple stimulus modalities, allows for a more complete evaluation of the relevance of these demographic factors to acute pain perception.

The Role of Chronic Psychosocial Stress in Explaining Racial Differences in Stress Reactivity and Pain Sensitivity

OBJECTIVE

To examine the role of psychosocial factors in mediating the relationship between African American (AA) race and both increased pain sensitivity and blunted stress reactivity.

METHODS

Participants included 133 AA and non-Hispanic white (nHW) individuals (mean [SD] age, 37 [9]) matched for age, sex, and socioeconomic status. Participants underwent mental stress testing (Trier Social Stress Test) while cardiovascular, hemodynamic, and neuroendocrine reactivity were measured. Participants completed questionnaires assessing potential sources of psychosocial stress and were tested for pain responses to cold pain and the temporal summation of heat pulses. Mediation analyses were used to determine the extent to which exposure to psychosocial stress accounted for the observed racial differences in stress reactivity and pain.

RESULTS

Chronic stress exposure and reactivity to mental stress was largely similar among AAs and nHWs; however, AAs exhibited heightened pain to both cold (p = .012) and heat (p = .004). Racial differences in the relationship between stress reactivity and pain were also observed: while greater stress reactivity was associated with decreased pain among nHWs, reactivity was either unrelated to or even positively associated with pain among AAs (e.g., r = -.21 among nHWs and r = .41 among AAs for stroke volume reactivity and cold pressor intensity). Adjusting for minor racial differences in chronic psychosocial stress did not change these findings.

CONCLUSIONS

Accounting for psychosocial factors eliminated racial differences in stress reactivity but not racial differences in sensitivity to experimental pain tasks. Increased exposure to chronic stress may not explain AAs' increased pain sensitivity in laboratory settings.

Muscle pain and blood pressure responses during isometric handgrip exercise in healthy African American and non-Hispanic White adults

It has been shown that African Americans (AAs) are more sensitive to experimental pain stimuli compared to non-Hispanic Whites (NHWs). A single bout of exercise results in naturally-occurring muscle pain and elevation in blood pressure (BP); however, it is currently unclear whether AAs and NHWs differ in muscle pain and BP responses during exercise. Therefore, we examined the differences in muscle pain and blood pressure (BP) during isometric handgrip exercise in African Americans (AAs) and non-Hispanic Whites (NHWs). Fourteen AAs and 14 NHWs completed isometric exercise consisting of squeezing a hand dynamometer at 25% of maximal strength for 3 min. During exercise, muscle pain ratings (MPRs) were assessed every 30s, whereas systolic and diastolic BP (SBP and DBP) were recorded every minute. During exercise, AAs generally reported greater MPR than NHWs (p<0.001), and MPR increased more rapidly during exercise in AAs than NHWs (p<0.05). In contrast, SBP and DBP continued to increase similarly during exercise in both AAs and NHWs (p>0.05). The results suggest that AAs generally experienced a greater intensity of muscle pain than NHWs during isometric handgrip exercise, but both groups exhibited similar elevations in BP during exercise.

Racial and ethnic differences in older adults with knee osteoarthritis

OBJECTIVE

Knee osteoarthritis (OA) contributes significantly to disability in older individuals, and racial/ethnic minorities are disproportionately affected. The present study aimed to characterize differences in clinical and experimental pain, including pain inhibition, among older African American (AA) and non-Hispanic white (NHW) subjects with knee OA.

METHODS

AA and NHW subjects with knee OA (n = 267) completed clinical and functional pain assessments, including quantitative sensory testing (QST). We hypothesized that, when compared to NHW subjects, AA subjects would display 1) lower pain tolerance and higher ratings of heat-, mechanical-, and cold-induced pain, 2) greater temporal summation of pain, 3) reduced pain inhibition, and 4) greater clinical pain and poorer function. In addition, we hypothesized that the findings from QST would significantly predict the severity of clinical pain within each race/ethnicity.

RESULTS

AA subjects with knee OA displayed increased pain sensitivity, greater temporal summation, and reduced pain inhibition when compared to NHW subjects with knee OA. Moreover, AA subjects reported greater clinical pain and poorer function. Racial/ethnic differences in clinical pain became nonsignificant when the analyses were controlled for education and annual income, whereas differences in QST findings remained highly significant. Although the extent of pain inhibition predicted the severity of clinical pain in both groups, different QST measures were additionally predictive of clinical pain within each group.

CONCLUSION

The results of this study establish that there are racial/ethnic differences in experimental and clinical pain and function in older individuals with knee OA. Our findings indicating that different QST measures were associated with clinical pain within the 2 racial/ethnic groups, whereas reduced pain inhibition was important in all participants, warrant further study in order to elucidate the common and group-specific pathophysiologic mechanisms contributing to clinical pain in OA.

Emotional reactions to pain predict psychological distress in adult patients with Sickle Cell Disease (SCD)

Differentiating somatic from emotional influences on the experience of chronic pain has been of interest to clinicians and researchers for many years. Although prior research has not well specified these pathways at the anatomical level, some evidence, both theoretical and empirical, suggest that emotional reactions influence the experience of disease and non-disease-related pains. Other studies suggest that treatments directed at negative emotional responses reduce suffering associated with pain. The current study was conducted to explore the influence of emotional reactions to pain as a predictor of psychological distress in a sample of adult Blacks with Sickle Cell Disease (SCD). Using cross-sectional survey data, we evaluated whether negative emotional reactions to the experience of pain were predictive of psychological distress after controlling for the somatic dimension of pain and age in n = 67 Black patients with Sickle Cell Disease (SCD). Results showed that greater negative emotion associated with pain predicted Somatization (p < .01), Anxiety (p < .05), Phobic Anxiety (p < .05), and Psychoticism (p < .05). Increased negative emotion associated with pain was also predictive of the General Symptoms Index (p < .05) and the Positive Symptoms Total from the SCL-90-R (p < .01). We believe the current study demonstrates that negative emotional reactions to the experience of pain in adults with SCD are predictive of psychological distress above and beyond the influences of age and the direct nociceptive experience. We also believe these data to be valuable in conceptualizing the allocation of treatment resources toward a proactive approach with early identification of patients who are responding poorly for the purpose of potentially reducing later psychopathology. A deeper understanding of the ways that subpopulations cope with chronic disease-related pain may produce models that can be ultimately generalized to the consumers of the majority of healthcare resources.

Experimental pain phenotype profiles in a racially and ethnically diverse sample of healthy adults

OBJECTIVE

To examine patterns of interindividual variability in experimental pain responses emerging from multiple experimental pain measures in a racially/ethnically diverse sample of healthy adults and to examine the association between the derived phenotype profiles with demographic, psychological, and health-related measures.

METHODS

Two hundred and ninety-one participants underwent heat, cold, pressure, and ischemic pain assessments, and completed several psychological and health-related assessments. The experimental pain measures were subjected to a principal component analysis and factor scores were used to compute Pain Sensitivity Index scores. The scores were subsequently submitted to a cluster analysis to identify patterns of pain sensitivity across experimental pain modalities.

RESULTS

The sample was equally composed of non-Hispanic whites, African Americans, and Hispanic whites. Sensitivity scores were computed for heat pain, pressure pain, cold pain, ischemic pain, and temporal summation of heat pain. Five distinct clusters were characterized by high heat pain sensitivity, low ischemic pain sensitivity, low cold pain sensitivity, low pressure pain sensitivity, and high temporal summation. Cluster membership was significantly different by sex as well as somatic reactivity and catastrophizing, although cluster differences were most pronounced between the heat pain-sensitive individuals vs the cold pain-insensitive individuals.

CONCLUSIONS

Our findings highlight the importance of phenotyping individuals to account for interindividual differences in pain responses. Our findings also replicate previously reported pain phenotypes, which are not solely related to demographic, psychosocial, or health-related factors in our healthy participants. Future studies designed to elucidate the biological underpinnings of pain sensitivity profiles would be of substantial value.

Cardiovascular responses to and modulation of pressure pain sensitivity in normotensive, pain-free women

Background and purpose The psychophysiological responses to and modulation of pressure pain stimulation are relatively new areas of investigation. The aims of the present study were to characterize subjective and cardiovascular (CV) responses to pressure pain stimulation, and to examine the relationship between CV responding and pain pressure pain sensitivity. Methods Thirty-nine pain-free, normotensive women were included in the study and tested during the follicular phase of their menstrual cycles. Pain threshold and tolerance were recorded at the right masseter muscle and the sternum, and visual analogue scales (VAS) were used to rate both pain intensity (the sensory dimension) and discomfort (the affective dimension). Mean arterial pressure (MAP), heart rate (HR), and facial and digital skin blood flux (SBF) were registered continuously. Results The pain threshold and tolerance were significantly higher at the sternum compared with the masseter, but the level of affective distress was higher at the masseter tolerance point. No associations emerged between pressure pain threshold and tolerance stimulation levels, and the corresponding VAS ratings. Pressure pain stimulation of the masseter induced significant increases in MAP, HR, and a decrease in digital SBF. During sternum pressure stimulation a significant change in HR and digital SBF was observed. There were no significant correlations between CV responding and pressure pain sensitivity. Conclusion Healthy women seem to display higher pressure pain sensitivity at the masseter region relative to the sternum. Pressure pain stimulation was associated with significant changes in MAP, HR, and SBF, but was not modulated by CV responses. The validity of these findings is strengthened by our control for menstrual cycle events, weekend-related changes in physiology, and CV changes during pain stimulation. Implications This study extends previous reports of SBF sensitivity to electrocutaneous pain into the field of pressure stimulation. Moreover, this study suggests that the often demonstrated association between high BP and low pain sensitivity may not apply to pressure pain specifically. Alternatively, this finding adds to the literature of gender differences in the relationship between CV responding and acute pain sensitivity in general.

Ethnicity interacts with the OPRM1 gene in experimental pain sensitivity

Robust interindividual variation in pain sensitivity has been observed, and recent evidence suggests that some of the variability may be genetically mediated. Our previous data revealed significantly higher pressure pain thresholds among individuals possessing the minor G allele of the A118G SNP of the mu-opioid receptor gene (OPRM1) compared with those with 2 consensus alleles. Moreover, ethnic differences in pain sensitivity have been widely reported. Yet, little is known about the potential interactive associations of ethnicity and genotype with pain perception. This study aimed to identify ethnic differences in OPRM1 allelic associations with experimental pain responses. A total of 247 healthy young adults from three ethnic groups (81 African Americans; 79 non-white Hispanics; and 87 non-Hispanic whites) underwent multiple experimental pain modalities (thermal, pressure, ischemic, cold pressor). Few African Americans (7.4%) expressed the rare allele of OPRM1 compared to non-Hispanic whites and Hispanics (28.7% vs. 27.8%, respectively). Across the entire sample, OPRM1 genotype did not significantly affect pain sensitivity. However, analysis in each ethnic group separately revealed significant genotype effects for most pain modalities among non-Hispanic-whites (P<.05) but not Hispanics or African Americans. The G allele was associated with decreased pain sensitivity among whites only; a trend in the opposite direction emerged in Hispanics. The reasons for this dichotomy are unclear; they may involve ethnic differences in haplotypic structure, or A118G may be a tag-SNP linked to other functional polymorphisms. These findings demonstrate an ethnicity-dependent association of OPRM1 genotype with pain sensitivity. Additional research is warranted to uncover the mechanisms influencing these relationships.

Ethnic differences in pain and pain management

Considerable evidence demonstrates substantial ethnic disparities in the prevalence, treatment, progression and outcomes of pain-related conditions. Elucidating the mechanisms underlying these group differences is of crucial importance in reducing and eliminating disparities in the pain experience. Over recent years, accumulating evidence has identified a variety of processes, from neurophysiological factors to structural elements of the healthcare system, that may contribute to shaping individual differences in pain. For example, the experience of pain differentially activates stress-related physiological responses across various ethnic groups, members of different ethnic groups appear to use differing coping strategies in managing pain complaints, providers' treatment decisions vary as a function of patient ethnicity and pharmacies in predominantly minority neighborhoods are far less likely to stock potent analgesics. These diverse factors, and others may all play a role in facilitating elevated levels of pain-related suffering among individuals from ethnic minority backgrounds. Here, we present a brief, nonexhaustive review of the recent literature and potential physiological and sociocultural mechanisms underlying these ethnic group disparities in pain outcomes.