Acute pain threshold in subjects with chronic pain following spinal cord injury.

Studies of pain perception in patients with chronic pain have yielded contradictory results. While several studies found that acute pain threshold is raised in chronic pain subjects, others showed that these subjects exhibit a decreased pain threshold compared to pain free subjects. The aim of this study was to further examine this topic by studying pain perception in subjects with chronic pain following partial or complete spinal cord injury (SCI). We found a significant elevation of heat-pain threshold (measured above the level of lesion) in complete SCI subjects with chronic pain (CSCIP) as opposed to complete SCI subjects without pain, incomplete SCI subjects with (ISCIP) and without chronic pain and normal controls. This elevation of pain threshold was completely reversed following a complete relief of the chronic pain by DREZ lesion. Moreover, the CSCIP exhibited significantly higher scores in the McGill pain questionnaire compared to ISCIP, indicative of a more intense chronic pain perceived by these subjects. In addition, the chronic pain below the level of spinal lesion, reported by CSCIP originated from a significantly larger body area than that of ISCIP. These results indicate that a critical level of chronic pain must be perceived in order to induce an elevation in acute pain threshold.