Assessment of Sensory Thresholds in Dogs Using Mechanical and Hot Thermal Quantitative Sensory Testing

Summary

This work describes a standard protocol for mechanical and hot thermal quantitative sensory testing to evaluate the somatosensory system in dogs. Sensory thresholds are measured using an electronic von Frey anesthesiometer, pressure algometer, and hot contact thermode.

Abstract

Quantitative sensory testing (QST) is used to evaluate the function of the somatosensory system in dogs by assessing the response to applied mechanical and thermal stimuli. QST is used to determine normal dogs' sensory thresholds and evaluate alterations in peripheral and central sensory pathways caused by various disease states, including osteoarthritis, spinal cord injury, and cranial cruciate ligament rupture. Mechanical sensory thresholds are measured by electronic von Frey anesthesiometers and pressure algometers. They are determined as the force at which the dog exhibits a response indicating conscious stimulus perception. Hot thermal sensory thresholds are the latency to respond to a fixed or ramped temperature stimulus applied by a contact thermode.

Following a consistent protocol for performing QST and paying attention to details of the testing environment, procedure, and individual study subjects are critical for obtaining accurate QST results for dogs. Protocols for the standardized collection of QST data in dogs have not been described in detail. QST should be performed in a quiet, distraction-free environment that is comfortable for the dog, the QST operator, and the handler. Ensuring that the dog is calm, relaxed, and properly positioned for each measurement helps produce reliable, consistent responses to the stimuli and makes the testing process more manageable. The QST operator and handler should be familiar and comfortable with handling dogs and interpreting dogs' behavioral responses to potentially painful stimuli to determine the endpoint of testing, reduce stress, and maintain safety during the testing process.

Introduction

Quantitative sensory testing (QST) assesses the responses elicited by externally applied stimuli; it is used to evaluate the function of the somatosensory system in humans and animals¹. Mechanical stimuli in the form of punctate pressure or deep pressure are applied as a ramped stimulus. The sensory threshold is determined as the force that evokes a psychophysical response¹. Hot or cold thermal stimuli can be used as a ramped stimulus or as a fixed intensity stimulus. The sensory threshold is determined as the temperature at which there is a response or the latency to respond to the stimulus. Punctate pressure sensory th....

Protocol

All procedures were approved by the Institutional Animal Care and Use Committee of North Carolina State University.

1. Room set-up and study subject acclimatization

1. Perform QST in a dedicated space where there is ample room for a QST operator, handler, and dog of any size to move about comfortably. Minimize potential auditory and visual distractions and use a white noise machine to block out ambient sound.
2. Place a large yoga mat or similar padding on the floor to ensure that the dogs are comfortable in lateral recumbency during testing.
3. Allow the dog at least 10 min to freely explore and acclimate to the room....

Results

Mechanical and thermal QST has been performed to detect sensory thresholds in both research and client-owned dogs under various clinical conditions, including normal, healthy dogs, dogs with chronically painful conditions such as OA, dogs with acute spinal cord injury, and to assess post-operative pain and effectiveness of analgesics. Though there is a growing body of work on QST in dogs, no normal range of values has been established for any testing modalities. However, several studies have assessed the feasibility and .......

Discussion

It is crucial to the acquisition of accurate data - that reflects the dog's sensory thresholds - that the dog is as calm, relaxed, and positioned adequately as possible for each measurement. A previous study noted that agitation from restraint or distraction from factors within or outside the testing environment affected dogs' responses to the QST stimuli¹⁶. If the dog becomes agitated from recumbency or restraint or is distracted, the dog should be given time to settle before a measuremen.......

Materials

Name	Company	Catalog Number	Comments
Electronic von Frey anesthesiometer	IITC Life Science Inc.	Item # 23931	Custom made with a 1000g max force load cell
Medoc Main Station software	Medoc	(supplied with TSA-II)
SMALGO: SMall Animal ALGOmeter	Bioseb	Model VETALGO
TSA-II NeuroSensory Analyzer	Medoc	DC 00072 TSA-II	No longer manufactured - new model is TSA-2 with same probes and same function