  Many individuals with chronic musculoskeletal pain (CMP) show impairments in
their pain-modulatory capacity. Although stress plays an important role in
chronic pain, it is not known if stress-induced analgesia (SIA) is affected in
patients with CMP. We investigated SIA in 22 patients with CMP and 18 pain-free
participants. Pain thresholds, pain tolerance and suprathreshold pain ratings
were examined before and after a cognitive stressor that typically induces pain
reduction (SIA). Whereas the controls displayed a significant increase in pain
threshold in response to the stressor, the patients with CMP showed no
analgesia. In addition, increased pain intensity ratings after the stressor
indicated hyperalgesia (SIH) in the patients with CMP compared to controls. An
exploratory analysis showed no significant association of SIA or SIH with
spatial pain extent. We did not observe significant changes in pain tolerance
or pain unpleasantness ratings after the stressor in patients with CMP or
controls. Our data suggest that altered stress-induced pain modulation is an
important mechanism involved in CMP. Future studies need to clarify the
psychobiological mechanisms of these stress-induced alterations in pain
processing and determine the role of contributing factors such as early
childhood trauma, catastrophizing, comorbidity with mental disorders and
genetic predisposition.
