Racial, ethnic variables shape the chronic pain experience

That depression, anxiety, sleep disorders and other neuropsychological conditions are often associated with chronic pain isn't news to most neurologists. But physicians who do not specialize in pain management are largely unaware of a growing body of research suggesting that a chronic pain patient's race (a genetic classification) or ethnicity (a cultural classification) may determine his or her risk of neuropsychological symptoms.

The complexities underlying the relationship between pain, race/ethnicity and neuropsychological comorbidity, which pain researchers are only beginning to explore, reflect the even more complex network of variables that represents what is known about the interconnections between race and pain in general. Apparent contradictions between laboratory results and population-based study findings suggest that racial or ethnic variations in the pain experience—the ways in which chronic pain affects a patient's quality of life—may be as important clinically as racial or ethnic differences in pain tolerance. However, some relationships that appear to have a racial or ethnic basis may in fact be more grounded in socioeconomic or cultural factors that may be more difficult for a clinician to ascertain.

Researchers are beginning to piece together the race-pain puzzle, as evidenced by the increasing numbers of studies being presented at Amercian Pain Society meetings and published in the medical literature. Much of what investigators are learning, however, has yet to trickle down to the level of the treating physician.

“With great efforts by the American Pain Society as well as others, more and more pain physicians are becoming increasingly aware of race/ethnicity as a factor in the management of pain,” said Charles E. Argoff, MD, director of the Cohn Pain Management Center at North Shore University Hospital on Long Island, NY, and assistant professor of neurology at New York University. “Non-pain physicians also need to be more aware of this and I think much more work needs to be done here as well.”

TESTING FOR TOLERANCE

In trying to understand the relationship between race and pain, one of the most basic questions researchers have been asking is whether patients of different racial backgrounds have different levels of pain tolerance and pain sensitivity. The answer, perhaps not surprisingly, is yes and no.

In a study of 30 Caucasian and 18 African American volunteers, researchers from the University of Alabama at Birmingham found that the African American subjects had significantly lower thermal pain tolerance and rated the lowest of the thermal stimuli as more unpleasant than did their Caucasian counterparts; however, they found no significant racial differences in thermal pain thresholds or pain intensities.¹ The findings are consistent with those of University of Florida researchers, who found that 62 African American volunteers had lower tolerance of thermal pain, cold pressor pain, and ischemic pain than 58 Caucasian subjects and had significantly higher ratings of unpleasantness and intensity for suprathreshold thermal pain.²

British investigators reported that 20 South Asian male volunteers had significantly lower thermal pain thresholds and experienced higher pain intensity than 20 Caucasian men, but found no statistically significant group differences for cold pain threshold or heat unpleasantness.³ Meanwhile, Danish researchers found significantly greater levels of pain intensity following capsaicin injection to the forehead (to induce migraine-like trigeminal sensitization) in 16 South Indian male volunteers than in 16 Caucasians; the size of the hyperalgesic area was also significantly larger in the South Indian subjects.⁴

REAL-WORLD RESULTS

Outside the laboratory, however, researchers have reached conflicting conclusions regarding ethnic or racial differences in pain intensity and pain severity. In a study of 712 chronic pain patients presented at the 2004 meeting of the APS, researchers from the Haley Veteran's Affairs Medical Center in Tampa, FL, reported that pain intensity ratings in Hispanic and African American patients were significantly higher than in Caucasian patients, although ratings for the two ethnic minority groups did not differ significantly from each other.⁵ And researchers from the University of Chicago found that 57 black patients with chronic pain had higher levels of pain severity than 207 Caucasian patients.⁶ However, separate studies from Arizona State University⁷ and Johns Hopkins University⁸ found no such ethnic discrepancies. The ASU researchers found no significant difference in pain severity between 214 non-Hispanic African American patients and 214 non-Hispanic Caucasian patients with chronic pain. And the Johns Hopkins investigators found that neither pain severity nor pain intensity differed significantly between groups of African American, Hispanic, and Caucasian patients with chronic pain.

COMORBIDITY COMPLEXITY

Research has been similarly inconsistent in its ability to conclusively link race or ethnicity to the risk of depression, anxiety, or other neuropsychological co-morbidities, with some studies demonstrating significant independent associations and others finding that racial and ethnic variables are inextricably linked to socioeconomic ones.

Investigators from the Houston Veterans Affairs Medical Center found significantly higher levels of depression in 128 non-Hispanic black patients with chronic pain than 354 non-Hispanic white patients, even after controlling for pain severity.⁹ But the aforementioned Johns Hopkins study⁸, which closely matched subjects for such confounding variables as education, work status, and pain duration, found no significant differences between African Americans, Hispanics and Caucasians in terms of depression scale scores. Researchers from Florida State University did not find that depression was independently associated with ethnicity, but did find that ethnic differences in pain report were exacerbated by depression, such that the difference in pain report between Hispanic and Caucasian patients with depression was greater than the difference between Hispanic and Caucasian patients who were not depressed.¹⁰

Carmen R. Green, MD, an associate professor of anesthesiology and a pain medicine physician at the University of Michigan, has seen such apparent contradictions within her own research. In a 2003 study presented at the APS meeting, Green and colleagues found that African American women with chronic pain not only had lower levels of pain but also were more likely than Caucasian women to experience depression or post traumatic stress disorder.¹¹ And in a 5750-patient study presented at the following year's APS meeting, they found that African Americans with chronic pain had significantly more difficulty falling asleep and reported worse overall sleep quality than their Caucasian counterparts.¹²

But in three studies presented in May at this year's APS meeting, Green and colleagues found that increased risk of depression in black men with chronic pain was due in large part to socioeconomic disadvantage.^13-15 Looking specifically at patients aged 50 and older, they found that although race was not associated with mood disorders, race was associated with lower socioeconomic status, which in turn was associated with a higher risk of mood disorders.¹⁴ And in a 2834-patient study, the relationship between race and emotional disorders was mediated by neighborhood advantage (percentage of residents with a college degree, percentage of annual household incomes above $100,000, and percentage of owner-occupied households) while race was found to be significantly associated with psychotic disorders independent of neighborhood disadvantage (percentage of unemployment, percentage of residents without a high school education, and percentage of annual household incomes below $5,000).¹⁵

PINPOINTING DISABILITY

The common denominator, according to Green, is disability: Those whose lives are disrupted to the greatest extent by chronic pain are most at risk for comorbidities, and her group's studies consistently show that African Americans with chronic pain experience greater levels of disability than their Caucasian counterparts.^11,13-17

“Depression is mediated through disability, so if you can control for that then the risk of depression does not increase,” Green said.

The Johns Hopkins researchers,⁸ who found no significant between-group differences in disability levels, surmised that the apparent discrepancy between their findings and others' (including those of Green et al) was likely due to the extent to which they controlled for confounding variables. To that end, the University of Chicago researchers also found significantly greater levels of disability in African American patients with chronic pain than in Caucasian patients; however, they also found that this significance disappeared when pain severity was controlled for.⁶ But the Johns Hopkins researchers also acknowledged that some of the disparaties between their findings and others' may stem from the use of different assessment tools. Specifically with regard to disability, they found no significant between-group differences using the Multidimensional Pain Inventory, but previously had found significant differences using the Oswestry Disability Questionnaire;¹⁸ Green and colleagues use the Pain Disability Index.

“People often believe that once you control for socioeconomic status some of these racial differences will go away,” Green said. “That's not consistent with the literature. The differences may narrow, but they do not go away.”

CLINICAL IMPLICATIONS

That said, Green and others believe that it is important for clinicians to consider a chronic pain patient's socioeconomic status and the circumstances under which he or she lives when determining treatment strategies. If the patient is the sole caretaker in his or her household, the stress of maintaining that level of care can exacerbate the stress of living with chronic pain. And for ethnic minorities, there is the added stress of racial discrimination to consider as well.

Previous research suggests that ethnic minorities may be less likely to seek treatment for their pain, whether through self-care or from a physician^19-23 (see sidebar).

“A lot of people have the mistaken belief that I don't want to bother the doctor, and that if I do it will take his or her attention away from my cancer or my other problems,” Green said. “That's something we see in particular in our minority population. They cope better but they feel they have less control over their pain.”

The Johns Hopkins study, while finding no statistically significant ethnic differences for most coping variables, did find that African Americans and Hispanic patients with chronic pain were more likely than Caucasians to use prayer as a coping strategy – and that use of prayer as a coping strategy was predictive of greater disability across all three ethnic groups.⁸

“Cultural, ethnic, and socioeconomic influences can contribute to a patient’s belief system, which will affect the neurologist-patient relationship and the patient’s compliance, trust, and response to future treatment,” said Peter Lars Jacobson, MD, clinical professor of neurology and director of the Palliative Care Program at the University of North Carolina in Chapel Hill. “A detailed past social history including previous experiences with physicians, thoughts about past treatments (both positive and negative) and possible future therapies would help to identify important racial/ethnic components that should be incorporated into a successful treatment plan.”

Experts also agree that clinicians should be vigilant in diagnosing and treating neuropsychological symptoms in all patients with chronic pain, regardless of race or ethnicity.

“Clinically, all patients with chronic pain need to be assessed for neuropsychological co-morbidities including depression, post-traumatic stress disorder, sleep disorders, and previous history of alcohol or drug dependence,” Jacobson said. “The treatment plan needs to approach these co-morbidities to be comprehensive and effective.”

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