Influences of gender role and anxiety on sex differences in temporal summation of pain

Previous research has consistently shown moderate to large differences between pain reports of men and women undergoing experimental pain testing. These differences have been shown for a variety of types of stimulation. However, only recently have sex differences been demonstrated for temporal summation of second pain. This study examined sex differences in response to temporal summation of second pain elicited by thermal stimulation of the skin. The relative influences of state anxiety and gender role expectations on temporal summation were investigated. Asymptomatic undergraduates (37 women and 30 men) underwent thermal testing of the thenar surface of the hand in a temporal summation protocol. Our results replicated those of Fillingim et al indicating that women showed increased temporal summation compared to men. We extended those findings to demonstrate that temporal summation is influenced by anxiety and gender role stereotypes about pain responding. When anxiety and gender role stereotypes are taken into account, sex is no longer a significant predictor of temporal summation. These findings highlight the contribution of social learning factors in the differences between sexes' pain perception.

PERSPECTIVE

Results of this study demonstrate that psychosocial variables influence pain mechanisms. Temporal summation was related to gender role expectations of pain and anxiety. These variables explain a significant portion of the differences between men and women's pain processing, and may be related to differences in clinical presentation.

Individual differences in diffuse noxious inhibitory controls (DNIC): association with clinical variables

Laboratory pain research has been criticized as being irrelevant to the clinical experience of pain. Previous findings have been inconsistent with some studies suggesting that experimental pain responses may be related to the reported presence or severity of chronic pain, while others report no such associations. However, few of these studies assess a variety of laboratory pain responses, and none has assessed relationships between clinical pain and diffuse noxious inhibitory controls (DNIC) in healthy subjects. We administered questionnaire measures of pain, quality of life, and psychological variables to a sample of healthy adults participating in a laboratory study of age differences in pain responses. DNIC was not related to other laboratory pain responses, psychological variables, or physiological variables measured in the present study. Regression models predicting health-related quality of life (e.g. pain, physical functioning) revealed that age, sex, and DNIC responses explained between 10 and 25% of the variance in these dependent measures. Of the laboratory pain variables, only DNIC was the sole consistent predictor of clinical pain and physical health, with greater DNIC responses related to less pain, better physical functioning, and better self-rated health. In addition, age differences in DNIC appeared to partially mediate age differences in physical functioning. These findings highlight the potential clinical relevance of experimental pain procedures and suggest that DNIC may be the laboratory pain response most closely associated with clinical pain and health-related variables.

Pain tolerance as a predictor of outcome following multidisciplinary treatment for chronic pain: differential effects as a function of sex

Sex-related differences in the experience of clinical and experimental pain have been widely reported. Females are at elevated risk for developing several chronic pain conditions and women demonstrate greater sensitivity to noxious stimulation in the laboratory. However, relationships between responses to experimental noxious stimuli and the experience of clinical pain have not been well characterized. One previous study of healthy adults indicated that pain threshold and tolerance were associated with clinical pain among women but not men (i.e. females with lower pain threshold and tolerance reported more clinical pain). In the present investigation, relationships between pain tolerance and outcomes of treatment for chronic pain were evaluated in a sex-dependent manner. Ischemic pain tolerance was assessed prior to treatment in 171 chronic pain patients completing a pain management program. Outcomes were measured as changes in pain severity, affect, and pain-related disability. Over the course of treatment, women demonstrated greater improvement in pain-related disability while men showed more reduction in pain. Ischemic pain tolerance was related to outcome in a sex-specific fashion. Women with higher pain tolerances showed greater improvement in pain, more reduction in pain-related interference, and more increases in activity level than women with lower pain tolerances. In contrast, pain tolerance was not associated with positive treatment outcomes among men. These results indicate that experimental pain responses may be most clinically relevant for women, and that sex differences may exist in the determinants of pain-treatment outcomes.

Sex differences in perceptual and cardiovascular responses to pain: the influence of a perceived ability manipulation

Sex differences in responses to experimental pain have been widely reported, with women typically showing lower pain threshold and tolerance than men. One possible explanation for these differences is that traditional gender roles may lead to sex differences in perceived ability to tolerate pain. To address this possibility, the present study evaluated the influence of a sex-related perceived ability manipulation on pain tolerance and cardiovascular responses to ischemic pain assessed via the submaximal effort tourniquet procedure. A sample of 68 young adults (35 women, 33 men) were randomly assigned to 1 of 2 perceived ability conditions, which depicted either women (FEM condition) or men (MASC condition) as more able to tolerate the painful task. The results indicated that men had higher pain tolerance than women. Although there was no overall effect of the experimental condition, only men in the FEM condition had higher tolerance than women. Also, men had greater blood pressure reactivity than women, and further analysis showed that women in the MASC condition had the lowest systolic blood pressure reactivity. Cardiovascular reactivity and motivation to tolerate the pain were positively correlated with pain tolerance only among men in the FEM condition. These findings indicate that the perceived ability manipulation produced only modest effects on pain tolerance and cardiovascular reactivity, but the relationship of cardiovascular and subjective responses to pain tolerance differed across conditions. These findings suggest that perceived ability may contribute to perceptual and cardiovascular responses to pain in a complex fashion, and further research to explicate these relationships is needed.

The unequal burden of pain: confronting racial and ethnic disparities in pain

CONTEXT

Pain has significant socioeconomic, health, and quality-of-life implications. Racial- and ethnic-based differences in the pain care experience have been described. Racial and ethnic minorities tend to be undertreated for pain when compared with non-Hispanic Whites.

OBJECTIVES

To provide health care providers, researchers, health care policy analysts, government officials, patients, and the general public with pertinent evidence regarding differences in pain perception, assessment, and treatment for racial and ethnic minorities. Evidence is provided for racial- and ethnic-based differences in pain care across different types of pain (i.e., experimental pain, acute postoperative pain, cancer pain, chronic non-malignant pain) and settings (i.e., emergency department). Pertinent literature on patient, health care provider, and health care system factors that contribute to racial and ethnic disparities in pain treatment are provided.

EVIDENCE

A selective literature review was performed by experts in pain. The experts developed abstracts with relevant citations on racial and ethnic disparities within their specific areas of expertise. Scientific evidence was given precedence over anecdotal experience. The abstracts were compiled for this manuscript. The draft manuscript was made available to the experts for comment and review prior to submission for publication.

CONCLUSIONS

Consistent with the Institute of Medicine's report on health care disparities, racial and ethnic disparities in pain perception, assessment, and treatment were found in all settings (i.e., postoperative, emergency room) and across all types of pain (i.e., acute, cancer, chronic nonmalignant, and experimental). The literature suggests that the sources of pain disparities among racial and ethnic minorities are complex, involving patient (e.g., patient/health care provider communication, attitudes), health care provider (e.g., decision making), and health care system (e.g., access to pain medication) factors. There is a need for improved training for health care providers and educational interventions for patients. A comprehensive pain research agenda is necessary to address pain disparities among racial and ethnic minorities.

Spousal responses are differentially associated with clinical variables in women and men with chronic pain

OBJECTIVES

Spousal responses have been related to clinical variables in patients with chronic pain. For example, solicitous responses from spouses have been associated with greater levels of pain and disability among patients with chronic pain. However, few investigators have determined whether spousal solicitousness produces different effects in women versus men with chronic pain. The present study examined pain reports, medication use, psychosocial factors, functional measures, and pain tolerance in patients with chronic pain.

METHODS

Subjects included 114 female and 213 male chronic pain patients, who described their spouses as either high or low in solicitousness on the Multidimensional Pain Inventory. Measures of pain severity, affective distress, physical function, medication use, and pain tolerance were examined in women and men with high versus low scores on spousal solicitousness.

RESULTS

Among males only, high spousal solicitousness was associated with greater numerical ratings of pain and greater self-reported disability compared with patients with low solicitous spouses. Among females only, the high spousal solicitousness patients showed lower pain tolerance, greater pain-related interference, poorer performance on functional tasks (eg, timed walking, lifting, and carrying tasks), and greater use of opioid medications. In both women and men, spousal solicitousness was associated with higher scores on the MPI pain severity scale.

DISCUSSION

These results extend previous findings demonstrating a relationship between spousal responses and patients' adjustment to pain; however, the pattern of these effects appears to be moderated by the sex of the patient. Implications for assessment and treatment of chronic pain are discussed.

Sex differences in analgesic responses: evidence from experimental pain models

BACKGROUND AND OBJECTIVE

Sex-related influences on the experience of pain have received considerable empirical attention. Women are at greater risk for several forms of clinical pain and exhibit greater perceptual responses to experimental pain. In recent years, investigators have turned their attention to the influence of sex-related factors on analgesic responses. The purpose of this review is to examine the literature on sex differences in analgesic responses, emphasizing findings from experimental studies.

METHODS

First, important methodological issues in laboratory pain research are presented, and sex differences in responses to experimentally-induced pain are briefly addressed. Next, previous data from non-human animal research and human experimental and clinical research related to sex differences in analgesia are discussed. Also, preliminary results are presented from an ongoing study in our laboratory examining analgesic responses in women and men.

RESULTS AND CONCLUSIONS

Both previous research and preliminary findings from our laboratory suggests that opioids produce greater analgesic responses in women than men. Potential mechanisms underlying sex differences in analgesia are proposed, and important directions for future research are suggested.

The melanocortin-1 receptor gene mediates female-specific mechanisms of analgesia in mice and humans

Sex specificity of neural mechanisms modulating nociceptive information has been demonstrated in rodents, and these qualitative sex differences appear to be relevant to analgesia from kappa-opioid receptor agonists, a drug class reported to be clinically effective only in women. Via quantitative trait locus mapping followed by a candidate gene strategy using both mutant mice and pharmacological tools, we now demonstrate that the melanocortin-1 receptor (Mc1r) gene mediates kappa-opioid analgesia in female mice only. This finding suggested that individuals with variants of the human MC1R gene, associated in our species with red hair and fair skin, might also display altered kappa-opioid analgesia. We found that women with two variant MC1R alleles displayed significantly greater analgesia from the kappa-opioid, pentazocine, than all other groups. This study demonstrates an unexpected role for the MC1R gene, verifies that pain modulation in the two sexes involves neurochemically distinct substrates, and represents an example of a direct translation of a pharmacogenetic finding from mouse to human.

Sex differences and incentive effects on perceptual and cardiovascular responses to cold pressor pain

OBJECTIVE

Sex differences in pain perception have been widely reported, with women typically displaying greater pain sensitivity than men, but the mechanisms underlying these differences remain unclear. One possible explanation suggests that men are more motivated to tolerate and suppress expressions of pain because of the masculine sex role, whereas the feminine sex role encourages pain expression and produces lower motivation to tolerate pain among women.

METHODS

To examine the influence of motivation on perceptual and cardiovascular responses to pain among women and men, different levels of monetary incentive (high vs. low incentive) were provided to a group of 81 healthy young adults undergoing the cold pressor pain procedure. It was anticipated that men would have greater endogenous motivation and would therefore be less affected by the external incentive.

RESULTS

Men had higher pain thresholds and tolerances and lower pain ratings than women, but the incentive condition produced no significant effect on pain responses. Resting blood pressure was positively correlated with pain tolerance among the low incentive group, whereas blood pressure reactivity to the cold pressor predicted pain tolerance in the high incentive group.

CONCLUSIONS

Thus, monetary incentive did not influence pain responses, but the relationship between cardiovascular measures and pain responses was influenced by the incentive manipulation. Potential explanations for the observed results are presented, and the implications for applying the biopsychosocial model to pain research are discussed.

Clinical characteristics of chronic back pain as a function of gender and oral opioid use

STUDY DESIGN

A cross-sectional analysis of data derived from patients with chronic spinal pain undergoing evaluation at a multidisciplinary pain treatment center was conducted.

OBJECTIVE

To determine whether pain severity, psychological status, and physical disability differed as a function of gender and opioid use, and whether the clinical correlates of opioid use differed in women and men with chronic back pain.

SUMMARY OF BACKGROUND DATA

Gender differences in the experience of pain have been widely reported. For example, in the general population, several chronic pain conditions are more prevalent among women than among men, and many experimental studies demonstrate lower pain thresholds and tolerances among women. In addition, recent evidence from studies of experimental and acute clinical pain suggests that responses to analgesic medications may differ in women and men.

METHODS

The sample consisted of 240 patients (35% women) with low back, upper back, or neck pain undergoing evaluation for treatment at a multidisciplinary pain center. The patients were classified as opioid or nonopioid users on the basis of self-report and medical record review. All the patients completed a battery of clinical assessments, including measures of pain severity, psychological adjustment, self-reported disability, functional tasks, and pain tolerance. Analyses were conducted to examine clinical variables as a function of gender and opioid use.

RESULTS

The results indicated that opioid use was associated with greater self-reported disability and poorer function in both women and men. However, the association of opioid use with affective distress differed between women and men. The women using opioids showed lower affective distress, whereas the opioid-using men reported greater affective distress. Opioid use was not associated with pain severity, although the women reported greater pain than men.

CONCLUSIONS

These findings indicate that both opioid use and gender are significant predictors of clinical status of patients with chronic spinal pain. More interesting, these two variables interact because opioid use was associated with increased affective distress among the men, but the reverse was true for the women. In addition, the women reported greater pain severity, which is consistent with some previous findings. Potential explanations for these findings are presented, and the practical implications are discussed.

Age-related differences in endogenous pain modulation: a comparison of diffuse noxious inhibitory controls in healthy older and younger adults

Despite decades of research, hundreds of studies, and a number of recent reviews, the effects of aging on the experience of pain remain poorly understood. Many prior investigators have reported increases in persistent pain conditions and diminished tolerance for certain types of laboratory-induced pain among the elderly. While explanations for these effects often propose senescent decrements in endogenous analgesic systems as a possible contributory mechanism, almost no direct empirical evidence for this hypothesis has yet emerged in human studies. The present investigation was designed to evaluate the existence and nature of these putative age-related differences in endogenous pain inhibition. Groups of healthy younger (n=45, mean age=21.6 years, range=18-25) and older (n=48, mean age=63.1 years, range=55-67) adults participated in a controlled, two-session laboratory assessment of diffuse noxious inhibitory controls (DNIC), a measure of endogenous pain inhibition. In this study, we examined age differences in the effects of concurrent cold pain on ratings of heterotopically presented repetitive noxious thermal stimuli. Interestingly, older adults demonstrated facilitation rather than inhibition of thermal pain during concurrent noxious cold stimulation while younger adults demonstrated some expected DNIC effects (i.e. a reduction in thermal pain ratings during heterotopic stimulation with noxious cold). Collectively, the findings of the present study suggest age-associated decrements in at least one form of endogenous analgesic response. If replicated, such findings of reduced pain-modulatory capacity in the elderly may partially explain age-related differences in the prevalence, severity, and impact of chronic pain.

The influence of athletic status and gender on experimental pain responses

To examine the role of athletic status and gender on experimental pain responses, 24 athletes (12 male, 12 female) and 24 nonathletes (12 male, 12 female) participated in 3 experimental pain tasks. After a series of psychologic inventories and demographic questionnaires, pressure pain thresholds (4 sites: pectoralis, trapezius, biceps, quadriceps), ischemic pain threshold and tolerance (lower arm), and cold pressor pain threshold and tolerance (lower arm) were assessed. No significant overall effects of athletic status or gender were identified for measures of pressure pain threshold. No group differences emerged for ischemic pain threshold. Athletes demonstrated significantly higher tolerance for ischemic pain, and cold pressor pain threshold and tolerance were higher among athletes than nonathletes. Overall analyses indicated higher pain thresholds and tolerance for cold pain among men than among women. A final interview found that many participants who approached the upper limits of these pain tasks reported using a competitive coping strategy.

Effects of age on temporal summation and habituation of thermal pain: Clinical relevance in healthy older and younger adults

Although the effects of aging on the experience of clinical pain seem relatively clear, investigations of age-related changes in pain perception using laboratory-based pain assessment procedures have yielded contradictory findings. One potential source of variability in this literature is the type of experimental noxious stimulus that is used. Although thermal pain thresholds are the most commonly reported measure of pain sensitivity, use of suprathreshold stimuli in pain assessment procedures may yield additional, more clinically relevant information concerning the effects of aging on the experience of pain. The present study examined the effects of age on temporal summation of both the intensity and unpleasantness of thermal pain at multiple stimulus temperatures. Specifically, responses to repetitive thermal stimuli delivered to the volar forearm at 47 degrees C, 50 degrees C, and 53 degrees C were assessed in 34 younger (mean age, 22.4 years) and 34 older (mean age, 62.2 years) healthy volunteers. Results suggested that for the 47 degrees C and 50 degrees C stimulus trains, older adults exhibited higher ratings of the intensity and unpleasantness of thermal pain and enhanced temporal summation of thermal pain relative to younger adults. Moreover, thermal pain sensitivity was inversely related to perceptions of general health and to reports of recent clinical pain among younger, but not older, subjects. Collectively these findings may indicate small, although potentially significant, age-related alterations in the plasticity of the central nervous system or endogenous pain-modulatory capacities.

Race, ethnicity and pain

The current paper provides a brief overview of research on the effects of race and ethnicity on pain. More specifically, the article reviews the utility of the concepts of race and ethnicity for pain research, suggests operational definitions of race and ethnicity, reviews the literature on the effects of race and ethnicity on laboratory and clinical pain, and provides suggestions for future research.

Gender role expectations of pain: Relationship to sex differences in pain

Empirical research supports the existence of sex differences in pain; yet these differences are poorly understood. Although biological mechanisms have been posited to explain variability, results of pain modeling manipulations suggest social learning may be a stronger influence on pain response. In this report we use the term sex to refer to the biological category of male or female. We use the term gender to refer to the socially acquired aspects of being male or female sometimes referred to as femininity and masculinity. This study investigated a new measure, the Gender Role Expectations of Pain questionnaire (GREP), which was designed to measure sex-related stereotypic attributions of pain sensitivity, endurance, and willingness to report pain. Subjects were 156 male and 235 female undergraduates at a southeastern university. Psychometric investigation of the questionnaire revealed a 5-factor solution that closely mirrored the theoretical construction of the items. Test-retest reliability was also shown for individual items on a separate sample of 28 subjects. Results supported hypotheses about gender role: both men and women rated men as less willing to report pain than women (F(1,389) = 336, P <.001); both men and women rated women more sensitive (F(1,389) = 9.5, P <.05) and less enduring of pain (F(1,389) = 65.7, P <.001) than men; and men rated their own endurance as higher than the typical man (F(1,389) = 65.7, P <.001). Sex accounted for 46% of the variance in willingness to report pain. Results suggest that the GREP distinguished between the socially learned reactions to pain for men and women. It is recommended that the influence of gender-related expectations for pain be assessed in all studies investigating human sex differences in pain.

Sex, gender, and pain: women and men really are different

Sex-related differences in the experience of both clinical and experimentally induced pain have been widely reported. Specifically, females are at greater risk for developing several chronic pain disorders, and women exhibit greater sensitivity to noxious stimuli in the laboratory compared with men. Several mechanisms have been proposed to account for these sex differences. Psychosocial factors such as sex role beliefs, pain coping strategies, mood, and pain-related expectancies may underlie these effects. In addition, there is evidence that familial factors can alter pain responses, and these intergenerational influences may differ as a function of sex. Sex hormones are also known to affect pain responses, which may mediate the sex differences. Although the magnitude of these effects has not been well characterized, there are potentially important practical implications of sex differences in pain responses. These implications are discussed, and directions for future research are delineated.

The association of hormone replacement therapy with experimental pain responses in postmenopausal women

Considerable experimental research suggests that ovarian hormones can influence pain perception, and recent epidemiologic and clinical research suggests that exogenous hormone use may influence the prevalence and severity of clinical pain among women. However, to date no studies have examined the influence of hormone replacement therapy (HRT) on experimental pain responses and recent pain complaints among postmenopausal women. In this study, self-reported recent pain and general health were obtained, and thermal pain responses were assessed in three groups of healthy older adults: (1) women on HRT, (2) women not on HRT (No-HRT), and (3) men. Results indicated no group differences in recent pain complaints or self-reported health, but differences emerged for measures of thermal pain perception. Specifically, HRT women showed lower pain thresholds and tolerances than No-HRT women and men, and the latter two groups did not differ from each other. The potential explanations and limitations of the observed findings are discussed.

Ethnic differences in pain tolerance: clinical implications in a chronic pain population

OBJECTIVE

Although numerous studies have independently examined ethnic differences in clinical and experimental pain, few have investigated differences in both sensitivity to controlled noxious stimuli and clinical pain reports in the same sample. The present experiment examined the effects of ethnicity (African American vs. white) on experimental pain tolerance and adjustment to chronic pain.

METHODS

Three hundred thirty-seven (68 African American and 269 white) patients with chronic pain referred to a multidisciplinary treatment center participated in the study. In addition to completing a number of standardized questionnaires assessing adjustment to chronic pain, participants underwent a submaximal effort tourniquet procedure. This experimental pain procedure yields a measure of tolerance for a controlled noxious stimulus (ie, arm ischemia).

RESULTS

African American subjects reported higher levels of clinical pain as well as greater pain-related disability than white participants. In addition, substantial group differences were observed for ischemic pain tolerance, with African Americans demonstrating less tolerance than whites. Correlational analyses revealed a small but significant inverse relationship between ischemic pain tolerance and the reported severity of chronic pain.

CONCLUSIONS

Collectively these findings support previous research revealing ethnic differences in responses to both clinical and experimental pain. Moreover, the present results suggest that enhanced sensitivity to noxious stimuli on the part of African Americans may be associated with ethnic differences in reported clinical pain, although the magnitude of ethnic differences was much greater for ischemic pain tolerance than for clinical pain measures.

Age-associated differences in responses to noxious stimuli

BACKGROUND

Although population-based studies typically report age-associated increases in clinical pain, laboratory-based pain assessment procedures generally indicate diminished pain sensitivity with age. The majority of these studies have utilized noxious thermal stimuli as the method of pain induction. However, other pain assessment methodologies, including ischemic pain induction, may have a more meaningful relationship to clinical pain. The present study examined the effects of age on responses to a variety of experimental noxious stimuli. In addition, relationships between cardiovascular measures and pain responses were investigated in both older and younger subjects.

METHODS

Responses to thermal, mechanical, and ischemic pain were assessed in 34 younger (mean age, 22.4 years) and 34 older adults (mean age, 62.2 years). In addition, relationships between resting blood pressure and pain responses were assessed separately for older and younger participants.

RESULTS

Although group differences in thermal and mechanical pain responses did not achieve statistical significance, older individuals demonstrated substantially lower ischemic pain thresholds and tolerances assessed via the modified submaximal effort tourniquet procedure (ps < .01). Overall, higher resting arterial blood pressures were associated with increased pain thresholds and tolerances, although relationships between blood pressure and ischemic pain variables were evident only for the younger group.

CONCLUSIONS

These findings indicate that age-related differences in responses to experimental noxious stimuli vary as a function of the pain induction task, with older individuals showing greater sensitivity to clinically relevant stimuli. In addition, the absence of a relationship between blood pressure and ischemic pain responses in older adults may suggest potential functional decrements in at least one endogenous pain-modulatory system.