Conditioned Pain Modulation Decreases Over Time in Patients With Neuropathic Pain Following a Spinal Cord Injury.
Martin Gagné, Isabelle Côté, Mélanie Boulet and 3 others
PMID 33016208WHAT IT FOUND
Descending pain inhibition decreased over rehabilitation in patients with neuropathic pain after spinal cord injury, but remained stable in those with only musculoskeletal pain.
Early pain levels did not predict later pain, suggesting impaired inhibition is a consequence of neuropathic pain rather than its cause.
Key findings
01Conditioned pain modulation efficacy decreased significantly from admission to discharge in the total sample, dropping from -30.4% to -12.9% inhibition.
02Pain inhibition decreased over time only in groups with neuropathic pain, while it stayed stable in participants with only musculoskeletal pain.
03Conditioned pain modulation at admission was not predictive of neuropathic pain intensity at discharge, arguing against impaired inhibition as a primary cause of pain development.
STILL TO COME
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What it does not show
The sample size was small, particularly for subgroup analyses (e.g., only 5 patients had neuropathic pain alone). The vast majority of patients (94% at admission) were taking opioids, which are known to affect pain modulation, making it impossible to separate the effect of the injury from the medication. The timing of assessments varied between patients because it depended on admission and discharge dates from rehabilitation, not a fixed time post-injury. Neuropathic pain was classified by physiatrists without using standardized screening tools like the DN4, which may affect the precision of pain type identification.
Declared interests
The authors declared no potential conflicts of interest. The study was funded by government and research institutes (CIHR, FRQS, IRP, etc.), not by commercial entities.
The easy way to misread this
Do not conclude that impaired pain inhibition causes neuropathic pain after spinal cord injury. The study found that inhibition decreased over time in those who already had pain, and early inhibition levels did not predict later pain, suggesting the deficit is likely a consequence of the pain condition rather than its origin.