Multimodal investigation of neuropathic pain mechanisms in focal spinal lesions.

Abstract

Objectives: Focal spinal cord lesions occur across a variety of neurological diseases including non-traumatic cervical myelopathies which can lead to neuropathic pain. Currently, the degree to which signs and symptoms of neuropathic pain correlate with functional impairments and/or anatomical deficits remains unclear. This study aimed to identify structural and functional determinants associated with neuropathic pain in individuals with focal spinal lesions.

Methods: Individuals fulfilling the diagnostic criteria of neuropathic pain were identified among individuals with cervical myelopathy presenting with focal spinal lesions. Lesion volume and the extent of structural damage affecting the spinothalamic tract, dorsal columns, dorsal horn, and ventral horn were evaluated with tract-specific MRI of the cervical spinal cord. Quantitative sensory testing (QST) (i.e., thermal/mechanical thresholds) was performed at the most affected skin area. Additionally, contact heat-evoked potentials (CHEPs) were acquired following stimulation at the most affected skin area to objectively assess the functional integrity of the spinothalamic tract.

Results: MRI-derived structural damage was similar for individuals with (n=8) and without (n=8) neuropathic pain in all regions of interest (p>0.05). Mechanical hyperalgesia upon QST was observed in both groups. However, functional preservation of the spinothalamic system, measured by CHEPs, was present in 87 % of individuals with neuropathic pain, compared to 38 % of pain-free individuals (p=0.039).

Conclusions: These observations suggest that segmental hyperexcitability resulting from structural spinal cord damage, in combination with residual sparing of spinothalamic afferents, may represent a key pathophysiological constellation contributing to central neuropathic pain following focal spinal lesions.