|Ph.D Student||Crispel Yonatan|
|Subject||Pre-Operative Psychophysical Testing of Pain Modulation|
for Prediction of Short and Long Term Post-
Operative Pain after Thoracotomy
|Department||Department of Medicine||Supervisor||PROF. David Yarnitsky|
|Full Thesis text - in Hebrew|
Background: Clinical observations indicate that diseases or injuries of similar severity can cause a wide range of pain experience, despite corresponding peripheral tissue damage. It has been reported that less efficient DNIC (diffuse noxious inhibitory control, pain reduction during exposure to another noxious stimulus administered to a remote body area) is associated with history of higher pain experience among healthy subjects. Moreover, recent evidence indicates that patients with idiopathic pain disorders demonstrate lower DNIC efficiency and enhanced TS (temporal summation, the change in pain perception along a 'train' of identical pain stimuli). This suggests that altered DNIC and TS might be relevant in the pathogenesis of these pain disorders. We also suggest that DNIC efficiency and level of temporal summation would be significant factors in the prediction of chronic pain development. To investigate this assertion, we chose the model of post-operative pain developing after thoracotomy, since these patients can be assessed at a pain-free stage before surgery, with a ‘naive’ pain modulation system not yet affected by the presence of induced clinical pain. Further, a substantial percent of them develops chronic pain, and of substantial intensities.
Methods: Comprehensive psychophysical assessment of pain modulation was performed on 84 patients, 1-3 days before thoracotomy. This included static and dynamic parameters: pain thresholds; suprathreshold magnitude estimation, TS (mechanical and thermal) and DNIC. Acute post operative pain was assessed, at rest and following provocation. Chronic pain was performed on 78 patients assessed at 26-52 weeks after surgery.
Results: negative correlation (r = -.496, p < 0.0005) found between DNIC and chronic postoperative pain. MTS correlated with acute postoperative activity provoked pain (r=.307, p < 0.005) and chronic postoperative pain (r=.280, p=0.014). We didn’t find any correlation between TTS, acute or chronic, postoperative pain or static and dynamic parameters. The dynamic parameters didn't reveal any interaction among themselves.
Conclusions: The main aim was to see if individual's pain modulation profile determines clinical pain. The dynamic set of tests revealed a positive correlation and predicted the acute and chronic post operative pain. This is, to the best of our knowledge, the first report on prediction of chronic pain, showing that the profile of pain processing determines the tendency of a patient to develop chronic pain.