Quantitative Sensory Testing in Animal Models of Chronic Pain: A Pilot Study

Introduction: Quantitative sensory testing (QST) evaluates the patient’s somatosensory profile. This pilot study aimed to compare the sensory sensitivity of healthy and affected dogs with chronic pain condition.

Materials and Methods: Static and dynamic QST included punctate tactile and mechanical threshold, and conditioned pain modulation (CPM) delta. Healthy client-owned dogs (n = 7) were evaluated twice in a day, 4 hours apart. Data from healthy dogs were compared with laboratory dogs before and after (9 weeks) surgically-induced osteoarthritis (OA) (n = 6) and client-owned dogs with natural osteosarcoma (OSA) (n = 8). Inferential statistics were done at 5% α-threshold, data are mean(SD).

Results: In healthy dogs, intra-class correlation coefficients for tactile and mechanical thresholds at the primary site were 0.96 and 0.36, respectively; and 0.89 for mechanical threshold at a distal site. A CPM effect was observed in healthy dogs: 8.89(0.58) N pre- versus 9.5(0.38) N post-conditioning stimulus (p = 0.032). Mechanical threshold of laboratory dogs at baseline was high 9.44(1.1) N with no CPM effect observed. Primary tactile allodynia was present in OA-induced dogs (p = 0.014), and mechanical threshold was decreased in OA-induced 2.72(0.74) N, and OSA dogs 6.69 (2.35) N; (p < 0.05 for both painful conditions). Secondary mechanical allodynia was noted in OA-induced dogs (p = 0.013). No CPM effect was observed in OSA or OA-induced dogs.

Discussion: Deficiency of descending inhibitory control is a risk factor for the development of chronic pain in people. Similar deficiency was noted in dogs with chronic pain. The lack of CPM effect of laboratory dogs at baseline suggests a situation of stress-induced analgesia.

Acknowledgement: This study was partially funded by Le Groupe Vétoquinol. The authors wish to thank the staff at ArthroLab Inc. and Centre Vétérinaire Rive-Sud, as well as the dogs who participated in these studies. Dr. Beatriz Monteiro is a recipient of the Vanier Canada Graduate Scholarship, and this program of research is funded (Pr. Eric Troncy) by the Natural Sciences and Engineering Research Council of Canada as well as the Canada Foundation for Innovation.