Attentional modulation fails to attenuate the subjective pain experience in chronic, unexplained pain

Abstract Background Chronic, unexplained pain is a common, ill-understood clinical problem. Increased sensitivity for pain and other stimuli is often implied as an underlying mechanism. Attentional processes influence central pain processing and might mediate hypersensitivity at a cerebral level. Aims To study patients with chronic, unexplained pain with respect to (a) subjective pain experience; (b) effects of attentional manipulation; (c) level at which alterations in pain processing occur: locally (symptomatic body region), or generalised. Methods We compared 16 patients with chronic, unexplained limb pain with 16 matched healthy controls. Pain thresholds to electrical stimuli were recorded. Subjects then received individually thresholded painful and non-painful stimuli, with manipulation of attention towards or away from pain. The intensity of pain perception was recorded by means of visual analogue scales (VAS). Pain thresholds and effects of Attention and Laterality on VAS scores were compared between groups by means of general linear modelling (restricted to 12 patients with unilateral pain and 12 controls). Results Distraction increased thresholds for pain in healthy volunteers, but this effect was significantly attenuated in patients. Significant interactions between attention-effects, stimulus laterality and stimulus intensity indicated that VAS scores for painful stimuli were attenuated during distraction in healthy controls, but not in pain patients. Conclusions Results support the notion that pain processing is enhanced in chronic, unexplained pain, and that the influence of attentional modulation on pain processing is attenuated. Potential cerebral mechanisms are changes in either attentional allocation or attention-mediated descending pain modulation. The changes seem to occur at a generalised level.