Promoting Gait Recovery and Limiting Neuropathic Pain After Spinal Cord Injury

Abstract

Most persons living with a spinal cord injury experience neuropathic pain in the months following their lesion, at the moment where they receive intensive gait rehabilitation. Based on studies using animal models, it has been proposed that central sensitization in nociceptive pathways (maladaptive plasticity) and plasticity related to motor learning (adaptive plasticity) share common neural mechanisms and compete with each other. This article aims to address the discrepancy between the growing body of basic science literature supporting this hypothesis and the general belief in rehabilitation research that pain and gait rehabilitation represent two independent problems. First, the main findings from basic research showing interactions between nociception and learning in the spinal cord will be summarized, focusing both on evidence demonstrating the impact of nociception on motor learning and of motor learning on central sensitization. Then, the generalizability of these findings in animal models to humans will be discussed. Finally, the way potential interactions between nociception and motor learning are currently taken into account in clinical research in patients with spinal cord injury will be presented. To conclude, recommendations will be proposed to better integrate findings from basic research into future clinical research in persons with spinal cord injury.

Assessments of sensory plasticity after spinal cord injury across species

“…Studies assessing maladaptive sensory changes after SCI in NHP suggest sensory changes resembling certain human features of central pain including: supraspinal hyper-responsiveness to at-level stimulation, evidence of below-level dysesthesia (depilitation, overgrooming), symptoms that wax and wane over time, and unresponsiveness to opioids[26,99]. However, future studies need to further investigate how the observed sensory changes reflect neuropathic pain phenotypes observed in humans after SCI [100]. …”

The Spinal Cord, Not to Be Forgotten: the Final Common Path for Development, Training and Recovery of Motor Function

“…Spinal cord plasticity also has been implicated in central pain syndromes, in particular after SCI (Baumbauer, Young, & Joynes, 2009a;Ferguson et al, 2012aFerguson et al, , 2012bMercier, Roosink, Bouffard, & Bouyer, 2017). Based upon animal models, the same mechanisms that lead to spinal plasticity following locomotor training occur due to the nociceptive (pain pathway) input that occurs during a traumatic spinal injury.…”

“…It is interesting that it appears there is an interaction between developing spinal cord locomotor pattern generators and maladaptive nociceptive processing, given that locomotor training reduces the sensitization to nociceptive stimuli (Ferguson et al, 2012;Mercier et al, 2017). However, the timing of training may be important because wellestablished, untreated, uncontrolled nociceptive input may also reduce the capacity to build central pattern generating circuitry through locomotor training (Ferguson et al, 2012).…”

Impact of Experimental Tonic Pain on Corrective Motor Responses to Mechanical Perturbations

“…In patients, tonic pain that may be aggravated by activity (but that does not occur in relation to specific movements) is observed mainly in patients with neuropathic pain, while phasic pain that is specifically associated with a given movement is more typically observed nociceptive musculoskeletal pain. While the effect of phasic musculoskeletal pain on movement is more intuitive and has been studied more extensively using experimental models such as hypertonic saline injection [1,4], neuropathic pain that is unrelated to movement has been shown to be associated with motor alterations in clinical populations or clinical models (e.g., phantom limb pain or neuropathic pain in individuals with a spinal cord injury or a stroke) [2,5]. Studying motor adaptation to this type of pain, using different experimental pain models such as capsaicin, is therefore also warranted.…”