Doctor of Philosophy in Experimental Medicine (PhD)
Investigating neurochemical patterns in relation to pain
Spinal cord injury is a devastating neurological condition that results in varying degrees of sensory and motor loss, along with other health complications. Neurological recovery after spinal cord injury is generally thought to be limited to the 6-9 month period after injury, and there are currently no approved pharmacological interventions to improve this recovery. Overlapping with a proposed “window of opportunity” for interventions, neuropathic pain can occur early after injury and necessitate pharmacological management. Among the management options, anticonvulsants are routinely administered.Utilizing longitudinal observational human spinal cord injury data, this thesis explored the effects of anticonvulsants on neurological recovery after spinal cord injury using mixed effects regression, and conduct a meta-analysis on the acute progression of neuropathic pain. The research studies within this thesis are bookended by an introduction and methodology section (Chapters 1 and 2) and the discussion (Chapter 7). In Chapter 3, I examined the effect of anticonvulsants and found a beneficial association with motor recovery contingent on administration at 4 weeks. A review of patient records revealed that the majority of anticonvulsants being administered were gabapentinoids (i.e. pregabalin and gabapentin). To further examine whether this effect was specific to gabapentinoids or obtained by all anticonvulsants, Chapter 4 examined a unique spinal cord injured population administered non-gabapentinoid anticonvulsants and found no statistically significant associations with neurological recovery. Chapter 5 included a chart review to examine the effect of gabapentinoid-specific administration, and found a continued beneficial association with motor score, as well as the sensory outcome of light touch. Further, this chapter identified that very early administration (e.g. within 5 days) was necessary to achieve the largest benefit. Finally, Chapter 6 produced a longitudinal framework of neuropathic pain progression in clinical trials.In short, this thesis presents novel findings regarding the administration of anticonvulsants after spinal cord injury, and the beneficial association of gabapentinoid-specific anticonvulsants on motor recovery. Further, it provides an advance in our understanding of neuropathic pain progression after injury and a framework to guide future clinical trials.
Objectively measuring pain has proven challenging, largely due to the subjective and multidimensional nature of pain. There is a pressing need to identify valid outcome measures to evaluate treatment modalities for individuals suffering from pain. Current treatment and diagnosis of pain conditions, are dependent on self-report measures. A critical limitation is the lack of mechanistic information from this measure. The objective of this thesis was to examine potential biochemical biomarkers that account for the variability of pain perception among healthy individuals. Specifically, to examine changes in excitatory neurotransmitter concentrations (glutamate and Glx: glutamate+glutamine) in the anterior cingulate cortex (ACC) using functional single voxel magnetic resonance spectroscopy during an in-scanner noxious intervention. Excitatory neurotransmitter values were quantified every 2 minutes, simultaneously, the rating of perceived pain intensity was recorded (using a 0-10 numeric rating scale) to examine the relationship of glutamate levels and pain perception. Results show individuals with higher baseline glutamate values report higher pain ratings, however when tracked dynamically no relationship is seen between glutamate (or Glx) levels and ratings of perceived pain intensity with the current methodology. While further research is needed, baseline glutamate values may prove useful in pre-treatment identification. For example, in clinical trials classifying high and low pain responders based on glutamate baseline values may provide insight into the variability of treatment responders.