Abstract
Complex regional pain syndrome (CRPS) is a chronic pain condition associating sensory, motor, trophic and autonomic symptoms in one limb. Cognitive difficulties have also been reported, affecting the patients’ ability to mentally represent, perceive and use their affected limb. However, the nature of these deficits is still a matter of debate. Recent studies suggest that cognitive deficits are limited to body-related information and body perception, while not extending to external space. Here we challenge that statement, by using temporal order judgment (TOJ) tasks with tactile (i.e. body) or visual (i.e. extra-body) stimuli in patients with upper-limb CRPS. TOJ tasks allow characterizing cognitive biases to the advantage of one of the two sides of space. While the tactile TOJ tasks did not show any significant results, significant cognitive biases were observed in the visual TOJ tasks, affecting mostly the perception of visual stimuli occurring in the immediate vicinity of the affected limb. Our results clearly demonstrate the presence of visuospatial deficits in CRPS, corroborating the cortical contribution to the CRPS pathophysiology, and supporting the utility of developing rehabilitation techniques modifying visuospatial abilities to treat chronic pain.
Highlights
Complex regional pain syndrome (CRPS) is a chronic pain condition associating sensory, motor, trophic and autonomic symptoms in one limb
Simple t-tests showed that point of subjective simultaneity (PSS) values were only significantly different from zero when visual stimuli were presented in near space and the hands placed next to them (t(13) = −3.582, p = 0.003, d = −0.96), showing that, in this condition, the visual stimulus appearing close to the affected limb had to be presented significantly earlier (M = −13.49, SD = 14.09 ms) than the stimulus appearing close to the unaffected limb to be perceived as occurring simultaneously
We investigated whether CRPS affects spatial perception, i.e. induces attentional biases to one side of space, by means of temporal order judgment (TOJ) tasks
Summary
Complex regional pain syndrome (CRPS) is a chronic pain condition associating sensory, motor, trophic and autonomic symptoms in one limb (for a review see ref. 1). When patients were asked to cross their hands over their body midline, perceptual judgements were biased to the detriment of the unaffected hand, as if the patients’ performance did not rely on the actual stimulation of the affected hand, but rather on the side of space in which the affected hand normally resides These results clearly show that somatosensory perceptual difficulties in CRPS, as illustrated by TOJ tasks, cannot be attributed to altered peripheral coding or spinal transmission of somatosensory inputs, but rather to deficits in their cognitive processing. For both the visual and the tactile tasks, temporal order would be judged to the advantage of the stimuli presented close to or on the unaffected hand, showing that spatial cognitive deficits observed in CRPS do affect the perception of the body, and extend to the external space surrounding it
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