A way to study the endogenous pain inhibition ability of the subject is catered via conditioned pain modulation (paradigm used in lab). This present study deals with the functionality of the endogenous modulation.

Disturbed endogenous pain modulation is likely one of the mechanisms underlying central hypersensitivity and might be a contributing factor for the development and maintenance of chronic pain. To our knowledge, no study has investigated endogenous pain modulation in both acute and chronic low back pain (LBP). We tested the hypothesis that endogenous pain inhibition is impaired in patients with acute and chronic LBP. 

We evaluated 40 patients with acute LBP, 34 patients with chronic LBP and 30 pain-free controls for their conditioned pain modulation (CPM), with pressure pain tolerance and cold pressor as test and conditioning stimulus, respectively. Measurements were repeated up to 10 minutes after cold pressor test. 

There was no difference in CPM among the groups immediately after cold pressor test. However, the decline in CPM effect was significantly faster in chronic and acute LBP patients than in controls, with no evidence for differences between pain groups. 

The present study provides evidence for some alterations of endogenous modulation in both acute and chronic LBP. CPM was still detected in both patient groups, indicating that endogenous modulation, although effective for a shorter duration, is partially functioning in patients with LBP.