Individual Differences in Experience and Treatment of Pain: Race, Ethnicity, and Sex

Clarification of Terminology

Race and ethnicity are often used interchangeably in both colloquial language and research. However, these represent two different constructs. Race refers to groups with common descent or heredity, shared physical characteristics, culture, and self-identity [e.g. non-Hispanic White/Caucasian, Black/African American, Asian, Native American/Native Canadian], whereas ethnicity indicates cultural groupings with a common language, religion, nationality, or heritage (e.g. Hispanic/Latinx). ^, In this chapter, we will use the term non-Hispanic White (NHW) to refer to anyone of White or Caucasian descent, African American (AA) to refer to anyone of Black or African descent, and Hispanic to refer to anyone of Hispanic descent or who identifies as Latinx. Similarly, sex and gender are not interchangeable. Sex is defined as the biologic phenotype an individual is born with that can be categorized as either male, female, or intersex, while gender is an individual’s expression of internal identification that may fall into preexisting social, behavioral norms. Gender consists of a set of cultural behaviors that society has assigned to a specific sex (e.g. cooking is considered a task for women while plumbing is a task for men); thus gender is a social construct. Gender is also viewed on a spectrum between male and female and can evolve throughout one’s lifetime. An individual’s sex and gender are not always synchronous; therefore an individual may have a natal sex that does not correspond with their expressed gender (see Fig. 11.1 ). In the current chapter, we will be addressing the influence of race, ethnicity, and sex on the experience, burden, and treatment of pain.

Racial and Ethnic Differences in Pain

Racial and ethnic differences in the pain experience are consistently demonstrated across experimental and laboratory-based studies. In the United States, much of this literature has focused on AA/NHW differences, and the results are not always consistent. In general, research has demonstrated that, compared to NHW individuals, AA individuals are more sensitive to nociceptive stimulation (i.e. lower thresholds) and less tolerant of pain overall, though these results have some variability based on the modalities and outcomes assessed. Groups of NHW individuals demonstrate, on average, a higher cold pain tolerance and provide lower pain ratings (i.e. thresholds) for cold-induced pain than do groups of AA individuals. Although there are not AA-NHW differences in heat-induced pain thresholds, NHW people show a higher heat-induced pain tolerance and provide lower suprathreshold heat pain ratings than AA people. Regarding pressure pain, AAs have lower pressure pain thresholds than NHWs. AAs also have a lower tolerance to ischemic pain than NHWs, though there are no differences in ischemic pain threshold. ^, AA participants in experimental pain studies also rate mechanical pricking pain as more intense than do NHW participants in such studies. In addition to these pain sensitivity measures, there are also AA-NHW differences in experimental measures of centralized pain facilitation and inhibitory pain modulation (i.e. temporal summation and conditioned pain modulation [CPM]). AA individuals demonstrate consistently higher temporal summation of pain than NHWs. However, the CPM literature is small and inconclusive; one study found that AAs showed less CPM than NHWs, but other studies found no racial/ethnic differences in CPM.

Although much of the disparities literature has focused on differences between AA and NHW individuals, there is some recent evidence of disparities in experimental pain sensitivity among Hispanics, Native Americans (NAs), and Asians. Asians consistently demonstrate a lower tolerance and higher suprathreshold cold pain ratings relative to comparison groups such as NHW. Hispanics also demonstrate lower pain tolerance and provide greater suprathreshold pain ratings relative to NHWs. Asian and Hispanic people also report lower threshold and tolerance for heat pain. ^, However, Asians have a higher pressure pain threshold than AAs. Few studies have compared experimental pain processing between NAs and other groups. Such studies have indicated that AAs reported higher electric pain thresholds and lower pain ratings than NHWs. There were no differences in temporal summation between NA and NHWs. Collectively, the literature on laboratory-based pain assessment suggests that individuals from racial and ethnic minority backgrounds (many of whom have likely experienced substantial discrimination and mistreatment) appears to suggest an overall increase in pain sensitivity among individuals from these minority groups relative to individuals reporting their ethnic/racial background as “White.”

Besides racial and ethnic disparities in experimental and laboratory-based pain, there are also considerable differences in the experience of clinical pain conditions. For example, osteoarthritis (OA) is an increasingly common painful musculoskeletal condition. While AAs show a greater likelihood to have both radiographically confirmed and symptomatic OA, NHWs have a higher age-adjusted prevalence of chronic pain overall than do AAs. This difference was negated when the researchers only considered high impact chronic pain (i.e. chronic pain that frequently limits life or work activities). Other studies show quite a different pattern. Numerous studies demonstrated that AAs and other minority groups report more severe acute and chronic pain. ^, Compared to NHWs, AAs report more pain from chronic conditions such as AIDS and glaucoma, greater postoperative pain, more pain sites and greater pain severity, depression, and disability, and have poorer outcomes on performance testing that is sensitive to the functional impact of chronic pain (e.g. timed-up-and-go task, 6 min walking test). ^{, ,} Disparities in clinical pain exist between NHW and other minority groups as well. For example, minority patients report more severe low back pain than do NHWs. While Hispanic individuals report fewer pain conditions and experience less pain interference than NHWs, they have more severe clinical pain, Hispanic individuals also report greater postoperative pain. Although studied to a lesser degree, Asians also report greater pain intensity than do NHWs, particularly for knee OA. NAs are also more likely to experience pain complaints than the general United States population. ^, Overall, the literature on acute and chronic clinical pain indicates that the experience and adverse impact of pain may be more frequent and severe in groups of individuals from non-White racial and ethnic backgrounds.

Sex and Gender Differences in Pain

Beyond race and ethnicity, the perception and experience of pain also vary as a function of sex. In laboratory settings, women demonstrate lower pain thresholds and tolerance and provide higher pain ratings for mechanical-, electrical-, thermal- (both heat and cold), and chemical-induced nociceptive stimulation than men. ^, In addition to these measures of general pain sensitivity, women also exhibit greater central pain facilitation (e.g. temporal summation of pain) and less effective endogenous inhibitory control of pain (e.g. CPM). ^, Moreover, women demonstrate a lower threshold for eliciting the nociceptive reflex, an involuntary spinal reflex resulting from electrical nerve stimulation.

Similar sex differences are found for clinical pain. Indeed, large epidemiologic studies across geographic regions indicate that pain is more frequently reported by women than men, women are more likely to seek treatment for pain, and that women consistently report higher pain ratings than men across diagnostic groups. There is a higher prevalence of numerous painful diseases among women. Women are nearly twice as likely to experience neuropathic pain than men. They are also more likely to experience musculoskeletal (MSK) pain and report greater pain severity among MSK conditions , across 17 countries and six continents, women had a higher prevalence of MSK pain (45%) than men (31%). This is specifically true for fibromyalgia, back pain, and osteoarthritis-related pain. ^, Women are also more likely to report pain across ten different anatomical regions and chronic widespread pain. They are also at higher risk of experiencing abdominal pain such as interstitial cystitis. In fact, there is a 3:1 female-to-male ratio of irritable bowel syndrome (IBS) prevalence. Regarding headaches, women are more likely to experience tension-type headaches and migraines. ^, These sex disparities are also prominent in post-procedural pain. Women not only experience greater acute pain following various procedures, including cholecystectomy, hernia repair, colonoscopy, general outpatient surgery, and orthopedic surgeries, but also greater chronic postsurgical pain following total knee arthroplasty (TKA). However, there are no sex differences in chronic postsurgical pain following total hip arthroplasty, gallbladder surgery, or hernia repair. There is also no consistent evidence for sex differences in cancer pain. Thus there appear to be discrepancies in sex differences depending on the nature of the pain and treatments received.

Racial and Ethnic Differences in Pain Treatments Provided

It is well documented that racial and ethnic minorities have disproportionately more unrelieved pain than NHWs. This is because of racial and ethnic differences in both the assessment administered and treatments prescribed for pain across various conditions and settings.

Traditionally, racial and ethnic minorities and other vulnerable groups (e.g. homeless) are more likely to seek and receive care in the emergency department (ED). However, the care they receive in the ED is not equivalent to that received by NHWs. The ED care delivered to individuals from racial and ethnic minority backgrounds is of consistently lower quality, as outlined below. For example, minority groups have longer wait times and are less likely to be admitted as inpatients than NHWs. Minority patients also wait longer to receive pain medications in the ED than do NHWs. Results of a recent meta-analysis including 13 studies of racial disparities in pain care in United States EDs found that AAs were 36% less likely, Hispanics 30% less likely, and Asians 42% less likely to receive analgesics than NHW patients with similar injuries and complaints. Similarly, AAs were 35% less likely and Hispanics 23% less likely than NHWs to receive opioids for acute pain. Moreover, NHWs are 82% more likely than AAs to be discharged with a prescription for analgesics and 98% more likely to be discharged with an opioid prescription. In fact, AAs are less likely to receive opioid prescriptions in the ED than any other group racial or ethnic group. Perhaps this is because providers are more likely to view AA patients as drug-seeking. Indeed, although ED staff perceive only 7%-9% of the general patient population to be opioid dependent, they believe that opioid dependence affects a substantially higher percentage, 13%-17%, of patients with sickle cell disease, a disease that primarily affects AA individuals. Moreover, 22% of ED physicians believe that more than half of patients with sickle cell disease are addicted to opioids despite only 2%-4% actually meeting the criteria for a substance use disorder. ^,

Across other treatment settings, AA individuals are twice as likely as other racial and ethnic groups to have their pain underestimated by the physicians. Minority patients are also less likely to be treated in pain clinics and receive comprehensive diagnostic and treatment for pain than NHWs. When minority patients are treated, they receive lower doses of analgesic medications, are less likely to receive opioids, and are less likely to undergo surgical procedures (e.g. joint replacement) ^{, ,} despite having a higher prevalence of painful conditions and reporting higher pain scores.

Sex Differences in Pain Treatment

Much like racial and ethnic minorities, women are at greater risk for the undertreatment of pain. They often receive less treatment, and the treatment they receive is less effective at providing pain relief. In one study in the ED, women were less likely to be prescribed opioid medication than men. Likewise, Hamberg and colleagues found that women with neck pain were more likely to receive non-specific somatic diagnoses and analgesic and psychoactive medication prescriptions, regardless of the sex of the provider. Other studies have found that pain treatment differs because of the interaction between patient and provider sex. In one study, female providers prescribed higher opioid doses for women than men with low back pain, whereas male providers prescribed higher doses for male patients. Another found that female providers were more likely to recommend psychosocial treatments (i.e. anti-depressants and mental health referrals) for female than male pain patients. ^, This is consistent with evidence suggesting that women may be more likely to be mistrusted and “psychologized” by their providers, regardless of the sex of the provider. Unfortunately, this only increases distress among female patients that then may contribute to a cycle of chronic pain. While relatively little research has examined the intersectionality of race and sex related to chronic pain, it appears likely that AA women may be at particular risk for undertreatment and for having their pain reports underestimated or dismissed.

Racial and Ethnic Differences in Pain Treatment Outcomes

Beyond disparities in how pain is treated, there are also disparities in treatment outcomes when treatments are provided. Pain interventions (both pharmacologic and nonpharmacologic) may cause disparate analgesic effects based on race, ethnicity, and sex. For example, compared to NHW individuals, AA individuals are not only less likely to opt for surgical treatment options such as a total joint replacement, but when AA individuals do receive treatment (e.g. hip and knee arthroplasty, spinal surgery), they also report greater pain intensity, pain-related disability, and pain frequency than NHW individuals. A retrospective study using data from the Spine Patient Outcomes Research Trial found that of patients with spine disorders those that underwent spinal surgery had an improved outcome compared to those in the nonoperative treatment group. However, of those in the surgical group, the NHW patients reported significantly greater improvement in pain outcomes than the AA patients.

The effect of race and ethnicity on surgical treatment outcomes are subject to the intersectionality of socioeconomic factors. Indeed, Goodman et al. used self-reported and census data to investigate the interaction between race and socioeconomic variables on the outcomes of TKA. They found that worse pain outcomes were associated with race and socioeconomic factors and that AA patients from poorer communities showed evidence of suffering from a double disparity.

The research on racial disparities in nonsurgical pain treatment outcomes is scant and shows mixed results. In a laboratory study of opioid analgesia, researchers found that AA participants showed a greater analgesic response to morphine and butorphanol than NHWs. Concerning multi-disciplinary pain treatment outcomes, evidence suggests no racial or ethnic differences in treatment efficacy, including a reduction in pain severity. For example, Cano et al. demonstrated that controlling for age, sex, and other social determinants of health still resulted in a lack of racial and ethnic differences. In contrast, Merry and colleagues found that NHW and AA patients experienced improvements in pain-related interference following multi-disciplinary pain treatment, but only NHW participants reported reduced pain severity. A study of a cognitive-behavioral self-management program for chronic back pain showed yet a different pattern of results. While NHW, AA, and Hispanic participants all showed improvements in disability, only Hispanic participants improved in pain intensity. Taken together, it is clear that racial and ethnic minority patients experience different outcomes from treatment than NHWs. However, the evidence does not provide a consistent pattern of disparities.

Sex Differences in Pain Treatment Outcomes

The literature, including several meta-analyses, describes sex differences in pain treatment outcomes, especially for opioid analgesia. One such review found that women have a lower opioid consumption post-surgically than do men. A meta-analytic review of 11 studies found that women not only self-administer lower daily doses of opioids via patient-controlled analgesia pump (PCA) but also receive lower daily doses of opioids for chronic non-cancer pain. Moreover, women experience greater morphine-induced analgesia than do men across experimental and clinical studies. Together, this suggests that women respond better to opioids and require lower amounts than men for both acute and chronic pain. However, it is important to note that women are also more likely to experience opioid-induced side effects and mortality than men, ^, which may result from their increased sensitivity to the effects of opioids.

Sex differences in response to surgical pain treatment are consistent. Overall, women fare worse than men across surgical types and outcomes. Among patients undergoing orthopedic surgery, women reported a greater “worse pain” intensity since surgery and more time spent in severe pain than did men. Similarly, women are more likely than men to have persistent post-surgical pain three months following orthopedic trauma surgery. Women also report higher pain than men following rotator cuff repair. However, these differences dissolve after one year. It is important to note that while others have also acknowledged sex differences in pain, disability, and quality of life following orthopedic surgery, with women experiencing worse outcomes than men, women consistently had greater pain, disability, and poorer quality of life pre-surgically. After controlling for baseline differences, there were no sex differences in symptom improvement. Thus it is important to identify presurgical factors that may differ between men and women that may be contributing to sex differences in postsurgical pain.

There is also evidence of sex differences in outcomes for nonpharmacologic pain interventions, although these results are more inconsistent. For example, response to inter-disciplinary pain management programs may differ by sex. Keogh and colleagues found that although inter-disciplinary pain management was effective at reducing pain for both men and women, men reported ongoing relief after three months, whereas women’s pain had returned. In other studies, however, women showed greater improvement than men in pain and pain-related disability following a multimodal pain management program. Thus sex differences in outcomes of multimodal treatment may depend on the specific outcome (pain severity vs. disability) and the timing of follow-up. However, it is important to note that across studies of these inter-disciplinary, multimodal pain treatment programs, most patients are female. Thus more research may be needed to better understand the effectiveness of such programs among men. Regarding other nonpharmacologic treatments such as physical therapy, conventional physical therapy (e.g. heat, cold, massage, stretching, electrotherapy, and exercise) has shown to be more effective for men while intensive dynamic exercises are more effective for women. There is also some evidence that women are more responsive to psychological pain interventions. For example, women undergoingcognitive-behavioral therapy showed improved quality of life, whereas men did not. Likewise, there is evidence that acceptance-based interventions for pain may be more helpful in reducing pain for women than men. Sex differences in the pain experience (e.g. coping, catastrophizing, negative affect) may explain some of these treatment differences. Specifically, psychological interventions often target pain mechanisms such as catastrophizing. Perhaps the changes in these constructs as a result of treatment vary by sex, thus resulting in more broad sex differences in treatment outcomes.

Contributing Factors to Racial, Ethnic, and Sex Disparities