Pain-related threat and safety learning are likely altered in the setting of chronic back pain (CBP). These findings were published in the Journal of Pain.
Patients (n=62) with CBP and healthy volunteers (n=61) were recruited by the University Hospital Essen in Germany. Participants filled out questionnaires assessing demographics, clinical characteristics, and psychological processing. Pain was delivered by heat and assessed on a 100 point Visual Analog Scale (VAS) as well as continuous skin conductance recordings. The investigators used a differential conditioning paradigm which established an association between visual cues and pain threat.
The CBP and control cohorts were aged mean 34.6 (range, 16-69) and 33.8 (range, 19-70) years, 71.0% and 65.6% were women, and 46.7% and 65.5% had finished high school, respectively. The CBP group reported more anxiety, depression, pain-related symptoms, and stress (all P £.023).
Among the CBP cohort, the average pain duration was 9.79 (range, 1-38) years, the pain intensity during the previous four weeks on a 10 point Numeric Rating Scale (NRS) was 4.99 (range, 2-8) points, and current pain was 3.38 (range, 0-8) points.
The participants with and without CBP did not differ on the basis of heat pain threshold, individually calibrated temperature, pain intensity rating, pain-related fear, or arousal.
During the habituation phase, valence ratings were comparable between cohorts.
During the learning phase, both groups learned differently (CBP cohort: b, 3.45±0.84; P <.001; control cohort: b, 6.02±0.84; P <.001). This differential learning was significantly weaker among participants with CBP (b, -2.57±1.19; P =.03).
Both cohorts exhibited significant increases in negative valence in response to the pain stimulation (both P <.001) and positive valence to no pain stimulation (CBP cohort: P =.05; control cohort: P <.001), however, these effects were less pronounced among participants with CBP (pain stimulation: b, -1.26±0.64; P =.05; no pain: b, 1.40±0.64; P =.03).
During extinction training, valence ratings returned to baseline levels among patients but were still elevated among controls. However, the slopes between groups did not differ, indicating a stronger conditioning effect among controls during acquisition training.
In general, all participants correctly identified cues which predicted the delivery or absence of pain and had significantly lower contingency ratings following extinction training (CBP cohort: b, -43.98±3.28; P <.001; control cohort: b, -46.68±3.33; P <.001) than acquisition training (CBP cohort : b, -10.96±3.34; P =.001; control cohort: b, -9.92±3.33; P <.001).
With increasing pain duration, there was a reduced slope in valence ratings in response to pain stimulation and associated with less extinction.
The study authors noted that their conditions (no pain vs pain) were relatively easy to distinguish and the CBP cohort was rather homogenous.
These data indicated that patients with CBP differentiated less between the threat of pain compared with those who do not have CBP. People living with chronic pain may have altered pain-related threats and safety learning.
Schlitt F, Schmidt K, Merz CJ, et al. Impaired pain-related threat and safety learning in patients with chronic back pain.Pain. Published online November 25, 2021. doi:10.1097/j.pain.0000000000002544