Race and sex differences exist among patients with chronic lower back pain (CLBP) in regard to pain sensitivity for mechanical punctuate pain, deep muscle hyperalgesia, and pain severity due to aftersensations from the mechanical punctate stimulus, according to a study in the Journal of Pain.
A group of researchers from the Department of Anesthesiology at Brigham and Women’s Hospital in Chestnut Hill, MA, identified 325 Black and non-Hispanic White (NHW) with CLBP for at least 6 months with pain intensity ranging from ≥3 out of 10 and low back pain being the most forefront pain complaint. Patients reported informed consent and completed a series of questions that assessed personal demographics, pain ratings, depression, and catastrophizing, followed by quantitative sensory testing (QST).
Depression was measured by the Beck Depression Inventory with ratings from 0 (no depression present) to 3 (severe depression present). The Pain Catastrophizing Scale (PCS) is a measure of cognitive and emotional responses to pain, rating from 0 (no pain at all) to 4 (constant pain). Participants ranked low back pain from 0 (no pain) to 100 (most intense pain) numeric rating scale at the beginning of the laboratory session.
Mechanical pain was assessed using weighted pinprick stimulators; patients rated the painfulness of the 1st, 5th, and 10th stimulus as well as painful after-sensations seconds following the final stimulus using the same 0-100 numeric rating scale. Response to deep pressure pain was ascertained via cuff pressure algometry (CPA), and participants provided pain intensity ratings (0-100) upon cuff inflation and every 30 seconds for 2 minutes.
The average pain for all of the patients (47% female, 27% Black) at the time of visit was 46/100. No significant sex differences were found in current pain ratings, average low back pain severity, depression, catastrophizing, education, or employment. Compared to NHW participants, Black participants were older (t323 = -2.49), expressed more severe depressive symptoms (t323 = -4.07,) and catastrophizing (t323 = -8.74).
Greater temporal summation for mechanical punctate pain (r=.161) was the most common pain rating at the time of the study visit, while greater deep muscle pain intensity ratings (r =.159) and pressure pain painful after sensations (r=.147) were both associated with average low back pain severity during the previous week.
Compared to males, female participants rated aftersensations from the mechanical punctate stimulus as more painful (F1,314 = 24.48) and required less pressure of cuff inflation to produce moderate levels of pain (F1, 310 = 25.24). Black participants expressed more significant pain intensity ratings for mechanical punctate probes (F1, 310 = 7.02), deep muscle pressure pain (F1,315 = 7.94), and aftersensations for mechanical punctate (F1,314 = 25.68) pain compared to NHW patients. Black participants demonstrated greater temporal summation for both mechanical punctate pain (F1,313 = 11.03) and deep muscle pressure pain (F1,314 = 11.53), as well as required less cuff inflation pressure to produce moderate levels of pain (F1,310 = 8.22). Black participants also endorsed greater catastrophizing than NHW participants (F1,309 = 52.01). No sex differences were found in catastrophizing.
“As expected, we found that compared to NHWs, Blacks demonstrated greater pain sensitivity for several measures of deep muscle hyperalgesia as well as mechanical punctate pain,” stated the authors. “However, there were only sex differences in two measures of pain sensitivity; compared to males, females required less pressure to produce deep muscle pain and rated aftersensations of mechanical punctate pain as more painful.”
Meints SM, Wang V, Edwards RR. Sex and Race Differences in Pain Sensitization among Patients with Chronic Low Back Pain [published online July 16, 2018]. J Pain. doi: 10.1016/j.jpain.2018.07.001