Are negative neurological signs actually a positive hint in post-surgical pain?
One of the complications of surgical procedures is the development of persistent postoperative pain (PPoP). The extent of surgery, tendency to catastrophize pain, and prior pain history may contribute to development of PPoP. Quantitative sensory testing (QST) can predict someone’s chance of developing PPoP .
In a recent study by Ghandi et al. from the McGill University in Montreal, data was collected from patients who underwent partial or complete lung resection through posterolateral thoracotomy. The goal of the study was to identify who is at risk for developing PPoP based on QST, and to follow the trajectory of appearance and resolution of neuropathic signs post-surgery.
Nerve loss-of-function after surgery
Patients were tested with QST prior to surgery and each month up to six months at the site of the surgery. Most patients had pain at the area of surgery immediately after the procedure. However, thermal QST using Medoc's TSA-II Neurosensory Analyzer, revealed signs of nerve loss-of-function over the period of the study: some patients became less sensitive to cold, warmth and heat pain at the surgery site.
Predicting persistent post-operative pain
The main factors that predicted PPoP were sleep impairment, anxiety, and pre-surgical neuropathic pain symptoms. However, the authors also focused on high-density QST in addition to psychological factors. Thermal QST was one of the measures that had distinguished between patients with and without persistent post-operative pain. About three-quarters of patients had little to no pain at six months post-surgery. Those mostly pain-free patients at six months had more negative sensory signs post-surgery, like a decreased sensitivity to warm and cold detection and heat pain as compared to those who suffered moderate pain and showed little to no sensory deficits.
To summarize, surprisingly, post-surgical thermal sensory deficits are more typical for those who will not suffer in the long term of PPoP.
 Yarnitsky et al. 2008 “Prediction of chronic post-operative pain: pre-operative DNIC testing identifies patients at risk.”
Gandhi, W., Pomares, F. B., Naso, L., Asenjo, J. F. and Schweinhardt, P. (2020) Neuropathic pain after thoracotomy: tracking signs and symptoms before and at monthly intervals following surgery. European Journal of Pain. pp. 1269-1289. ISSN 1090-3801 doi: https://doi.org/10.1002/ejp.1569 Available at http://centaur.reading.ac.uk/90697/
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