Surgical and medical procedures, mainly those associated with nerve injuries, may lead to chronic persistent pain. Currently, one cannot predict which patients undergoing such procedures are 'at risk' to develop chronic pain. We hypothesized that the endogenous analgesia system is key to determining the pattern of handling noxious events, and therefore testing diffuse noxious inhibitory control (DNIC) will predict susceptibility to develop chronic post-thoracotomy pain (CPTP). Pre-operative psychophysical tests, including DNIC assessment (pain reduction during exposure to another noxious stimulus at remote body area), were conducted in 62 patients, who were followed 29.0+/-16.9 weeks after thoracotomy. Logistic regression revealed that pre-operatively assessed DNIC efficiency and acute post-operative pain intensity were two independent predictors for CPTP. Efficient DNIC predicted lower risk of CPTP, with OR 0.52 (0.33-0.77 95% CI, p=0.0024), i.e., a 10-point numerical pain scale (NPS) reduction halves the chance to develop chronic pain. Higher acute pain intensity indicated OR of 1.80 (1.28-2.77, p=0.0024) predicting nearly a double chance to develop chronic pain for each 10-point increase. The other psychophysical measures, pain thresholds and supra-threshold pain magnitudes, did not predict CPTP. For prediction of acute post-operative pain intensity, DNIC efficiency was not found significant. Effectiveness of the endogenous analgesia system obtained at a pain-free state, therefore, seems to reflect the individual's ability to tackle noxious events, identifying patients 'at risk' to develop post-intervention chronic pain. Applying this diagnostic approach before procedures that might generate pain may allow individually tailored pain prevention and management, which may substantially reduce suffering.

Descending modulation of pain can be demonstrated psychophysically by dual pain stimulation. This study evaluates in 31 healthy subjects the association between parameters of the conditioning stimulus, gender and personality, and the endogenous analgesia (EA) extent assessed by diffuse noxious inhibitory control (DNIC) paradigm. Contact heat pain was applied as the test stimulus to the non-dominant forearm, with stimulation temperature at a psychophysical intensity score of 60 on a 0-100 numerical pain scale. The conditioning stimulus was a 60s immersion of the dominant hand in cold (12, 15, 18 degrees C), hot (44 and 46.5 degrees C), or skin temperature (33 degrees C) water. The test stimulus was repeated on the non-dominant hand during the last 30s of the conditioning immersion. EA extent was calculated as the difference between pain scores of the two test stimuli. State and trait anxiety and pain catastrophizing scores were assessed prior to stimulation. EA was induced only for the pain-generating conditioning stimuli at 46.5 degrees C (p=0.011) and 12 degrees C (p=0.003). EA was independent of conditioning pain modality, or personality, but a significant gender effect was found, with greater EA response in males. Importantly, pain scores of the conditioning stimuli were not correlated with EA extent. The latter is based on both our study population, and on additional 82 patients, who participated in another study, in which EA was induced by immersion at 46.5 degrees C. DNIC testing, thus, seems to be relatively independent of the stimulation conditions, making it an easy to apply tool, suitable for wide range applications in pain psychophysics.

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Background and Objectives: Despite the established association between greater pain catastrophizing and enhanced postoperative pain, it is still unclear: (i) what is the relative contribution of each of the pain catastrophizing scale (PCS) dimensions in the prediction of acute and chronic postoperative pain; and (ii) whether PCS scores mediate the association between acute and chronic postoperative pain intensity. Methods: The current prospective, observational study was conducted at Rambam Health Care Campus, Haifa, Israel. PCS was obtained in 48 pain-free patients a day before an elective thoracotomy in response to tonic heat pain. Acute postthoracotomy pain (APTP) was assessed during rest, including general pain (Restgeneral), and incision-related pain (Restincision), and in response to provoked physical activity, including hand elevation (Provokedhand) and cough (Provokedcough). Chronic postthoracotomy pain (CPTP) was assessed after 4.5±2.3 months. Results: Of the PCS subscales, only rumination: (i) was correlated with Restgeneral scores (r=0.337, P=0.027); and (ii) predicted chronic postthoracotomy pain in a regression analysis (P=0.001). General PCS and its subscales mediated the correlation between Restgeneral and chronic postthoracotomy pain intensity (Ps<0.006). Conclusions: Findings may elucidate the unique role of the rumination subscale in reflecting an individual's postopertive acute and chronic pain responsiveness. The transition from acute to chronic postoperative pain seems to be facilitated by enhanced pain catastrophizing.

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