Quantitative Sensory Testing in an Observational Cohort of Adults With Chronic Low Back Pain.

BACKGROUND

Quantitative Sensory Testing (QST), also known as psychophysical testing, includes standardized methods for assessing humans' perceptions of different types of sensory stimuli and their associated pain thresholds. QST results can be used to estimate altered or atypical sensory processing and thus can be useful for determining pain mechanisms such as nociplastic or central nervous system-mediated pain. The University of Pittsburgh Mechanistic Research Center, entitled, "Low Back Pain: Biological, Biomechanical, Behavioral Phenotypes (LBP)," is part of the National Institutes of Health's Helping to End Addiction Long-term Initiative. LBP conducted a prospective, observational cohort study to identify phenotypes of over 1000 participants with cLBP. QST was conducted on these participants as part of comprehensive data collection. This article reports on the results of the QST procedures performed at the initial in-person enrollment visit.

METHODS

Four QST procedures were administered to participants of the LBP study at their enrollment visit: (1) Pressure Pain Thresholds (PPT) over the participant-reported site of lumbar pain (paraspinals) and a control site (trapezius) using an analog algometer; (2) Temporal Summation (TS) over the lumbar pain and control sites (forearm) using a Neuropen with a 40-g monofilament; (3) Conditioned Pain Modulation (CPM) using a cold water (5°C) immersion tank; and (4) Cold Water Tolerance time. A subset of LBP participants was excluded from the CPM and cold-water immersion procedures due to medical comorbidities such as cardiovascular disease and diabetic neuropathy. Means and standard deviations (SDs) were calculated from three trials of PPT and TS, two trials of CPM, and one trial of cold-water immersion time. TS was calculated by subtracting the numeric pain scores (0-10 scale) of the first from the 10th pinpricks. CPM was calculated by subtracting the mean trapezius algometer readings during the PPT procedure from those of the trapezius PPT during cold-water immersion.

RESULTS

The final cohort of QST participants was 999 adults. The mean/SD of lumbar and trapezius PPTs was 4.6 (2.4) and 4.4 (1.9) kg/cm, respectively. The mean/SD of lumbar and forearm TS was 1.6 (2.0) and 1.2 (1.8). Lingering pain after the 10th pinprick (after-sensations) was reported by 19.3% and 15.6% of participants after a series of 10 pinpricks was applied to the lumbar pain site and control site, respectively. The mean/SD CPM was 0.9 (1.2) with a wide range of CPM values from -2.9 to 5.9. The cold-water tolerance test resulted in a bimodal distribution, with 83% of participants having an average immersion time of 30 s and the remaining 17% reaching the maximum immersion time of 180 s.

CONCLUSIONS

QST data were collected from a large cohort of individuals with cLBP who participated in the LBP observational study. The QST results provide reference values for persons living with cLBP.