Chronic stress and cortical responsiveness to suprathreshold heat: fMRI-based evidence for stress management in pain rehabilitation

Background:Maximizing patient outcomes while shortening treatment duration is an ongoing challenge for physical therapists and their patients. A successful outcome following physical therapy is dictated by patient-reported outcomes and perceived pain intensity, which may be influenced by countless physiological, psychological, and environmental factors. Although physical therapists may successfully treat the anatomic origin of pain, the perception of painmay persist in the absence of injury (central sensitization). The overall literature suggests that chronic stress may initiate, exacerbate, or prolong the pain experience. Stress may decrease pain modulation or increase cortical responsiveness to aversive stimuli, resulting in central sensitization. Patients experiencing central sensitizationmay be unaware of the non-anatomic contributions to their pain, develop a fear of pain, and learn to avoid movements that reproduce pain. Therefore, to maximize patient outcomes and shorten treatment duration, it is important that patients be educated about the psychological contributions to pain. Therefore, the present analysis seeks to provide evidence for the effect of perceived stress on cortical responsiveness to repeated pulses of suprathreshold heat stimuli, a commonmeasure of central sensitization (temporal summation). Purpose: Using functional magnetic resonance imaging (fMRI), the goal of the present analysis is to examine the effect of chronic stress on central sensitization in pain-free volunteers. We hypothesize that subjects reporting higher levels of stress within the previous month will demonstrate increases in cortical responsiveness to suprathreshold heat. Our results may be utilized by physical therapists to educate patients about the role of stress in the pain experience, promote stress management as an adjunct to physical therapy, and maximize patient-reported outcomes. Methods: 11 healthy volunteers completed the Perceived Stress Scale (PSS), a validated measure of chronic stress, prior to undergoing fMRI of the brain during a validated protocol designed to measure central sensitization (temporal summation). During fMRI scanning, subjects experienced 4 bouts of 6 suprathreshold heat pulses (max temperature = 51 ◦C) separated by 90 second rest periods. Multiple regression and independent samples t-tests were used to examine the relationship between PSS scores and brain activity during heat pulses. Results:Perceived stress significantly predicted increased activation of cingulate cortex during heat pulses as compared to rest (k= 1202, x= 45, y= 12, z= 6, p 10 demonstrated a greater response in the cingulate cortex as compared to subjects with a PSS score <10 (k= 1202, x= 45, y= 12, z= 6, p< .001 FWE-corrected). Conclusion(s): These preliminary findings suggest that participants with higher levels of stress are likely to demonstrate increased responsiveness to potentially noxious stimuli in the cingulate cortex of the limbic system. Increases in pain sensitivity, prior to pain onset, may predispose individuals to a magnified pain experience and poor outcomes following physical therapy intervention. Implications: Physical therapists may utilize these findings to educate patients about the role of stress in the pain experience, promote stress management in pain rehabilitation, and maximize physical therapy outcomes. Ultimately, the integration of stress management in pain rehabilitation may prevent the transition from acute to chronic pain and improve quality of life.