Replicate Effects and Test–Retest Reliability of Quantitative Sensory Threshold Testing in Dogs with and without Chronic Pain

Introduction: Quantitative Sensory Testing (QST) is a promising method for assessing the mechanisms that contribute to chronic OA-associated pain. However, the effect of replicate (repetition) has not been evaluated, nor has repeatability. Our objective was to prospectively evaluate replicate effects and test–retest reliability of mechanical and thermal QST in normal dogs and dogs with OA-associated pain.

Methods: Mechanical (Electronic von Frey [EVF] and blunt pressure) and thermal (hot and cold) sensory thresholds were obtained in OA (n = 31) and control dogs (n = 23) at two visits, 7 days apart. Thresholds were measured at the affected joint (hip or stifle), over the tibial muscle, and over the metatarsals. Five replicates were obtained for each modality at each site bilaterally.

Results: Using a repeated measures, mixed model statistical approach, we did not find a significant effect of replicate on QST response. EVF thresholds were significantly lower at the second visit in OA dogs (affected and metatarsal sites, p = 0.0017 and p = 0.0014, respectively). For control dogs, EVF thresholds were significantly lower at the second visit at the metatarsal site, p = 0.001. Significantly higher second visit hot thermal latencies were seen in OA dogs at affected and tibial sites (p = 0.014 and p = 0.012, respectively) and control dogs at tibial site (p = 0.004).

Conclusions: In QST, replicate does not show a strong effect. However, QST results show variability over time, particularly for Electronic von Frey and hot thermal stimuli. If QST is to be used clinically to evaluate a sensitized state, the variability over time needs to be accounted for in study design.

Acknowledgements: This study was funded by the Comparative Pain Research Laboratory at the North Carolina State University College of Veterinary Medicine (instruments), Morris Animal Foundation (salary support under Grant No. D13CA-406) and Boehringer Ingelheim Vetmedica (screening of dogs under Grant No. BI-43041162). ESH was supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1144081. MEG receives funding support from the National Institutes of Health Ruth L. Kirschstein National Research Service Award (T32OD011130). The authors thank Ms Lyndy Harden for assistance in the collection of data.