Interplay between body schema, visuospatial perception and pain in patients with spinal cord injury

Background Changes in body representations (body image and/or body schema) have been reported in several chronic musculoskeletal pain syndromes, but rarely in patients with neuropathic pain and never in patients with spinal cord injury (SCI)-related pain. Methods We used implicit motor imagery (the laterality judgement task and visuospatial body perception tests) in 56 patients with thoracic SCI with (n = 32) or without (n = 24) pain below the level of the injury, and in a group of matched healthy controls (n = 37). We compared the participants' reaction time and the accuracy with which they identified the laterality of hands and feet presented in various orientations. Visuospatial body perception was assessed with a series of tests referred to as the 'horizontal subjective body midline', and the umbilicus-reaching task (URT), in which participants were asked to estimate the location of the umbilicus under different experimental conditions. Results Both groups of patients had longer reaction times for the identification of laterality for the feet than for the hands, but with no difference in accuracy. This longer reaction time was not correlated with spinal lesion severity, but was directly related to both average pain intensity and specific neuropathic pain components. The URT was affected in both groups of patients, with no effect of pain intensity. By contrast, the horizontal subjective body midline task was unaffected. Conclusion These results suggest an interplay between lower body scheme distortions and pain in patients with SCI. Significance Spinal cord injury is associated with alterations of lower body scheme as assessed with the laterality judgement task, which are directly related to pain intensity in patients with below-level neuropathic pain.