Central sensitization in spinal cord injured humans assessed by reflex receptive fields

• People with spinal cord injury can develop central sensitization, despite lacking supraspinal input and altered spinal/supraspinal processing.
• Reflex receptive fields are significantly larger and display a distinct different topography in spinal cord injured volunteers compared to non-injured volunteers.
• Protective plastic mechanisms may still be functional in people with spinal cord injury.

ObjectiveTo investigate the effects of central sensitization, elicited by intramuscular injection of capsaicin, by comparing the reflex receptive fields (RRF) of spinally-intact volunteers and spinal cord injured volunteers that present presensitized spinal nociceptive mechanisms.MethodsFifteen volunteers with complete spinal cord injury (SCI) and fourteen non-injured (NI) volunteers participated in the experiment. Repeated electrical stimulation was applied on eight sites on the foot sole to elicit the nociceptive withdrawal reflex (NWR). RRF were assessed before, 1 min after and 60 min after an intramuscular injection of capsaicin in the foot sole in order to induce central sensitization.ResultsBoth groups presented RRF expansion and lowered NWR thresholds immediately after capsaicin injection, reflected by the enlargement of RRF sensitivity areas and RRF probability areas. Moreover, the topography of the RRF sensitivity and probability areas were significantly different in SCI volunteers compared to NI volunteers in terms of size and shape.ConclusionsSCI volunteers can develop central sensitization, despite adaptive/maladaptive changes in synaptic plasticity and lack of supraspinal control.SignificanceProtective plastic mechanisms may still be functional in SCI volunteers.