Placebo hypoalgesia: racial differences

Abstract

No large-cohort studies that examine potential racial effects on placebo hypoalgesic effects exist. To fill this void, we studied placebo effects in healthy and chronic pain participants self-identified as either African American/black (AA/black) or white. We enrolled 372 study participants, 186 with a diagnosis of temporomandibular disorder (TMD) and 186 race-, sex-, and age-matched healthy participants to participate in a placebo experiment. Using a well-established paradigm of classical conditioning with verbal suggestions, each individual pain sensitivity was measured to calibrate the temperatures for high-and low-pain stimuli in the conditioning protocol. These 2 temperatures were then paired with a red and green screen, respectively, and participants were told that the analgesic intervention would activate during the green screens to reduce pain. Participants then rated the painfulness of each stimulus on a visual analog scale ranging from 0 to 100. Racial influences were tested on conditioning strength, reinforced expectations, and placebo hypoalgesia. We found that white participants reported greater conditioning effects, reinforced relief expectations, and placebo effects when compared with their AA/black counterparts. Racial effects on placebo were observed in TMD, although negligible, short-lasting, and mediated by conditioning strength. Secondary analyses on the effect of experimenter-participant race and sex concordance indicated that same experimenter-participant race induced greater placebo hypoalgesia in TMDs while different sex induced greater placebo hypoalgesia in healthy

Evidence for alterations to dynamic quantitative sensory tests in patients with chronic temporomandibular myalgia: A systematic review of observational studies with meta‐analysis

“…Of the 23 studies included (Table 1), nine studies used the Diagnostic Criteria for TMD (DC/TMD) to diagnose TMDm 25–34 10,35–47 .…”

Quantitative Sensory Testing Across Chronic Pain Conditions and Use in Special Populations

“…Alongside the promise of QST in improving the characterization of pain, and in turn, the prescription of individualized treatment interventions, limitations of this methodology must also be addressed. As highlighted in our descriptions of QST in TMD and placebo research, sex and racial effects regarding pain sensitivity, and racial effects regarding placebo efficiency have been observed, and thus need be accounted for when analyzing results ( 57 , 58 ). In addition, effects of age must be considered when incorporating QST, as loss of sensory function has been observed in older adults for cold, warmth, mechanical, and vibratory detection thresholds ( 90 ).…”

“…Recently, we assessed thermal heat pain threshold and thermal heat pain tolerance in TMD participants as a proxy for the QST procedure. We found that Afro-American Blacks had lower pain tolerance in both TMD participants and healthy control participants ( 57 ). Additionally, we found women in the TMD cohort to have lower levels of both thermal heat pain threshold and thermal heat pain tolerance than men ( 58 ).…”

“…Interestingly, the occurrence of placebo effects in both groups was not attributed to participant expectations, but rather to their prior experiences of having received the painful stimuli ( 74 ). In a study conducted to explore racial differences in pain and placebo effects, when compared to Whites, Afro-American Blacks demonstrated less efficient placebo hypoalgesia ( 57 ) and lower thermal heat tolerance. Importantly, there was a significant interaction with the race of the experimenters and the race of TMD participants hinting to potential healthy inequities and not just mechanisms of nociception.…”

“…Importantly, there was a significant interaction with the race of the experimenters and the race of TMD participants hinting to potential healthy inequities and not just mechanisms of nociception. Moreover, QST varies in Afro-American Blacks but this variation is not linked to placebo effects ( 57 ).…”