Development and initial validation of a sensory threshold examination protocol (STEP) for phenotyping canine pain syndromes

Quantitative sensory testing in canine musculoskeletal pain: Findings from a systematic review, meta-analysis feasibility assessment, and limitations

Quantitative sensory testing (QST) allows the study of pain mechanisms, patient phenotyping, and response to therapy. The goals of this study were to conduct a systematic review of the use of QST in dogs with musculoskeletal disease including osteoarthritis (OA), and to assess, by means of a meta-analysis, the ability of QST to differentiate affected dogs from healthy controls. The study protocol was registered; three bibliographic databases were screened. Studies involving QST in healthy dogs and those with musculoskeletal disease were included. Data were extracted using a standardized form. Assessment of quality and risk of bias were performed using the CAMARADES critical assessment tool. Twenty-nine articles met the inclusion criteria [systematic review (n = 11); meta-analysis (n = 28)]. In the systematic review, ten studies performed static QST: mechanical [punctate tactile (n = 6); mechanical pressure (n = 5)]; thermal [cold (n = 3); hot (n = 4)]; electrical (n = 1); and one study performed dynamic QST [conditioned pain modulation (n = 1)]. Most studies were of good scientific quality and showed low to moderate risk of bias. A meta-analysis was not possible due to numerous and severe issues of heterogeneity of data among studies. Methods to reduce risk of bias and use of reporting guidelines are some of the most needed improvements in QST research in dogs. Standardization of QST methodology is urgently needed in future studies to allow for data synthesis and a clear understanding of the sensory phenotype of dogs with and without chronic pain including OA.

Evaluation of Quadratus Lumborum Block as Part of an Opioid-Free Anaesthesia for Canine Ovariohysterectomy

Simple Summary

The aim of this study was to assess an anaesthetic protocol involving the quadratus lumborum block (QLB) for canine ovariohysterectomy. Ten healthy dogs were included. Anaesthetic protocol consisted of medetomidine and meloxicam, induction of anaesthesia with propofol and maintenance with sevoflurane in oxygen/medical air. The QLB was performed at the level of L₁–L₂ injecting 0.4 mL kg⁻¹ of 0.25% bupivacaine/iohexol per side. Computed Tomography (CT) was performed before and after surgery. Fentanyl was administered as rescue analgesia during surgery. The Short Form of The Glasgow Composite Pain Scale and thermal threshold (TT) at the level of the humerus, T₁₀, T₁₃ and L₃ were assessed before premedication and every hour postoperatively. Methadone was given as rescue analgesia when it was needed. CT images showed spreading of a median (range) of 3 (2–5) vertebrae, without differences between preoperative and postoperative images. One out of ten dogs needed intraoperative rescue analgesia. Pain score was less than 4/24 in all the animals until four hours after surgery. TT showed significative increase in all the areas tested apart from the elbow 30 min after the recovery. The QLB provides additional analgesia for canine ovariohysterectomy.

Abstract

Quadratus lumborum block (QLB) is used to provide analgesia for abdominal surgery in humans. The aim of this study was to assess an anaesthetic protocol involving the QLB for canine ovariohysterectomy. Ten dogs were included. Anaesthetic protocol consisted of premedication with IM medetomidine (20 μg kg⁻¹) and SC meloxicam (0.1 mg kg⁻¹), induction with propofol to effect, and maintenance with sevoflurane in oxygen/medical air. QLB was performed injecting 0.4 mL kg⁻¹ of 0.25% bupivacaine/iohexol per side. Computed Tomography (CT) was performed before and after surgery. Fentanyl was administered as rescue analgesia during surgery. The Short Form of The Glasgow Composite Pain Scale and thermal threshold (TT) at the level of the elbow, T₁₀, T₁₃ and L₃ were assessed before premedication and every hour postoperatively. Methadone was given as rescue analgesia postoperatively when pain score was >3. A Yuen’s test on trimmed means for dependent samples was used to analyse the data (p < 0.05). CT images showed spreading of the contrast/block for a median (range) of 3 (2–5) vertebrae, without differences between preoperative and postoperative images. One dog needed rescue analgesia during surgery. Pain score was less than 4/24 in all the animals during the first 4 h after surgery. TT showed a significant increased signal in all the areas tested, apart from the humerus, 30 min after surgery. The QLB may provide additional analgesia for canine ovariohysterectomy. Further studies are needed to assess the specific contribution of the QLB in abdominal analgesia.

Prospective Evaluation of Local Sustained Release of Celecoxib in Dogs with Low Back Pain

Back pain affects millions globally and in 40% of the cases is attributed to intervertebral disc degeneration. Oral analgesics are associated with adverse systemic side-effects and insufficient pain relief. Local drug delivery mitigates systemic effects and accomplishes higher local dosing. Clinical efficacy of intradiscally injected celecoxib (CXB)-loaded polyesteramide microspheres (PEAMs) was studied in a randomized prospective double-blinded placebo controlled veterinary study. Client-owned dog patients suffering from back pain were treated with CXB-loaded (n = 20) or unloaded PEAMs ("placebo") (n = 10) and evaluated by clinical examination, gait analysis, owners' questionnaires, and MRI at 6 and 12 weeks follow-up. At 6 and 12 weeks, CXB-treated dogs experienced significantly less pain interference with their daily life activities compared to placebo. The risk ratio for treatment success was 1.90 (95% C.I. 1.24-2.91, p = 0.023) at week 6 and 1.95 (95% C.I. 1.10-3.45, p = 0.036) at week 12. The beneficial effects of CXB-PEAMs were more pronounced for the subpopulation of male dogs and those with no Modic changes in MRI at inclusion in the study; disc protrusion did not affect the outcome. It remains to be determined whether intradiscal injection of CXB-PEAMs, in addition to analgesic properties, has the ability to halt the degenerative process in the long term or restore the disc.

Serum artemin is not correlated with sensitivity within dogs with naturally occurring osteoarthritis pain

Osteoarthritis (OA) pain is associated with peripheral and central sensitization in humans and results in widespread increased sensitivity across the body. Sensitization contributes to the OA-associated pain (OAP) state. We recently identified increased levels of an endogenous neurotrophic factor, artemin (ARTN), in dogs with OAP compared to healthy pain-free controls. Circulating ARTN released from damaged tissues in OA, may play a central role in widespread sensitivity and pain. However, the relationship between ARTN and somatosensory sensitivity remains unknown. The study aimed to assess the relationship between serum ARTN concentrations and measures of sensitivity in dogs with OAP using quantitative sensory testing. We hypothesized that there would be a positive association between circulating ARTN and increased sensitivity to mechanical and thermal stimuli in dogs with OAP. We used linear and logistic regression models to assess the relationship between ARTN, sensitization, and pain within a cohort of 43 dogs with spontaneous OAP. Serum ARTN was not associated with the degree of sensitization within dogs with OAP. Further, across dogs with varying OAP severity, we did not find any association between ARTN, and clinical measures of joint pain and disability. Although a relationship between ARTN and joint pain was not ruled out.

Remote Controlled Nociceptive Threshold Testing Systems in Large Animals

Simple Summary

Measurement of the nociceptive threshold (NT) is widely used in the study of pain and its alleviation. This records the intensity of a stimulus that causes pain to the test subject. The end point of the test that indicates when the subject experiences pain, the NT, is a behavioural escape response. Detection of a reliable and repeatable response depends on the animal behaving normally throughout testing. Restraint and an unfamiliar environment may prevent the animal from displaying normal behaviour and impede acquisition of robust NTs. Remotely controlled testing enables NT data to be collected from unrestrained animals behaving normally. Development of a remote controlled system for measurement of thermal and mechanical NTs in a range of large animal species is described. Normal “baseline” thermal and mechanical NTs from untreated animals are reported. This information can be used to improve both the welfare of the animals under investigation and the quality of the data collected. Remote controlled systems are now in use worldwide in both the study of pain physiology and in developing new pharmaceutical and non-drug-based methods of pain relief.

Abstract

Nociceptive threshold (NT) testing is widely used for the study of pain and its alleviation. The end point is a normal behavioural response, which may be affected by restraint or unfamiliar surroundings, leading to erroneous data. Remotely controlled thermal and mechanical NT testing systems were developed to allow free movement during testing and were evaluated in cats, dogs, sheep, horses and camels. Thermal threshold (TT) testing incorporated a heater and temperature sensor held against the animal’s shaved skin. Mechanical threshold (MT) testing incorporated a pneumatic actuator attached to a limb containing a 1–2 mm radiused pin pushed against the skin. Both stimuli were driven from battery powered control units attached on the animal’s back, controlled remotely via infra-red radiation from a handheld component. Threshold reading was held automatically and displayed digitally on the unit. The system was failsafe with a safety cut-out at a preset temperature or force as appropriate. The animals accepted the equipment and behaved normally in their home environment, enabling recording of reproducible TT (38.5–49.8 °C) and MT (2.7–10.1 N); precise values depended on the species, the individual and the stimulus characteristics. Remote controlled NT threshold testing appears to be a viable refinement for pain research.

Quantitative sensory testing of the equine face

BACKGROUND

Quantitative sensory testing methods are now standard in the evaluation of sensory function in man, while few normal equine values have been reported.

OBJECTIVES

The aim of this experimental study was (a) to define the tactile sensory, mechanical nociceptive and thermal nociceptive thresholds of the equine face; (b) to assess the effect of age, sex, stimulation site and shaving; (c) to evaluate the reliability of the methods and (d) to provide reference facial quantitative sensory testing values.

STUDY DESIGN

Method description.

METHODS

Thirty-four healthy Warmblood horses were used in the study. Six (tactile sensory threshold) and five (mechanical nociceptive and thermal nociceptive thresholds) areas of the left side of the face with clear anatomical landmarks were evaluated. Ten horses had two (mechanical nociceptive threshold) or three (tactile sensory and thermal nociceptive thresholds) of these areas shaved for another study. A linear Mixed model was used for data analysis.

RESULTS

All thresholds increased with age (tactile sensory threshold: by 0.90 g/y (CI = [0.12 g; 0.36 g]) P = .001; mechanical nociceptive threshold: by 0.25 N/y (CI = [0.13-0.36 N]) P = .000; thermal nociceptive threshold: by 0.2°C/y (CI = [0.055-0.361]) P = .008). Sex had no effect on thresholds (tactile sensory threshold: P = .1; mechanical nociceptive threshold: P = .09; thermal nociceptive threshold: P = .2). Stimulation site affected tactile sensory and mechanical nociceptive thresholds (P = .001 and P = .008), but not thermal nociceptive threshold (P = .9). Shaving had no significant effect on any of the thresholds (tactile sensory threshold: P = .06; mechanical nociceptive threshold: P = .08; thermal nociceptive threshold: P = .09).

MAIN LIMITATIONS

Only the left side was investigated and measurements were obtained on a single occasion.

CONCLUSIONS

Handheld quantitative sensory testing does not require shaving or clipping to provide reliable measurements. Stimulation over the nostril (tactile sensory threshold), temporomandibular joint (mechanical nociceptive threshold) and supraorbital foramen (thermal nociceptive threshold) resulted in the most consistent thresholds.

Interobserver agreement of an electronic von Frey device for measuring mechanical sensory thresholds in normal dogs

Electronic von Frey Aesthesiometry (VFA) has been previously reported as a useful method of mechanical quantitative sensory testing (QST) for evaluating neuropathic pain in dogs. Intraobserver agreement has been shown to be good to excellent; however, interobserver agreement has not been evaluated and is vital to the use of this technique in multicenter veterinary clinical trials in neuropathic pain. The goal of this study was to evaluate the interobserver agreement of sensory thresholds obtained using electronic VFA in a group of normal small breed dogs. Twenty healthy dogs (<20 kg) were recruited from the general practice population at the Ohio State University Veterinary Medical Center. Three clinically experienced yet QST novice evaluators used an electronic von Frey device to measure mechanical sensory threshold (ST) after a standardised training session conducted by an expert evaluator. Each dog was assessed by all three evaluators on the same day with both evaluator and limb test order randomised and testing sessions separated by 5 min. Mean ST values were averaged for all four limbs to produce a single value per dog for comparison between evaluators. Agreement between evaluators was determined using the intra-class correlation coefficient (ICC; two-way model for consistency, single measures). ICC across all three evaluators was 0.48, indicating moderate agreement. Moderate interobserver agreement is not sufficient to support the use of this technique in multi-center clinical trials, and our results underscore the importance of using a single evaluator for this QST technique until better agreement can be demonstrated.

Pregabalin for the treatment of syringomyelia-associated neuropathic pain in dogs: A randomised, placebo-controlled, double-masked clinical trial

Pregabalin is the first-line treatment for neuropathic pain (NeP) in humans. Dogs with Chiari-like malformation and syringomyelia (CM/SM) associated with NeP could benefit from pregabalin. The aim of this study was to evaluate the efficacy of pregabalin for NeP in dogs with CM/SM. Eight dogs with symptomatic CM/SM were included in a double-masked, randomised, crossover placebo-controlled clinical trial. All dogs received anti-inflammatory drugs as base-line treatment during placebo or pregabalin phase of 14±4 days each. Analgesic efficacy was assessed with a daily numerical rating scale (NRS) recorded by dog owners (0-10, 10=worst pain) and quantitative sensory testing at baseline, placebo and pregabalin phases. Blood samples were collected to report pregabalin exposure and to assess renal function. Daily NRS scores recorded by dog owners in the pregabalin group were lower than in the placebo group (P=0.006). Mechanical thresholds were higher with pregabalin compared to baseline or placebo (P=0.037, P<0.001). Cold latency at 15°C was prolonged on the neck and humeri with pregabalin compared to baseline (P<0.001 for both) or placebo (P=0.02, P=0.0001). Cold latency at 0°C was longer on pregabalin compared to baseline and placebo (P=0.001, P=0.004). There was no pregabalin accumulation between first and last dose. This study demonstrates the efficacy of pregabalin for the treatment of NeP due to CM/SM on daily pain scores recorded by dog owners. Pregabalin significantly reduced mechanical hyperalgesia, cold hyperalgesia (0°C) and allodynia (15°C) compared to placebo. Pregabalin was non-cumulative and well tolerated with occasional mild sedation.

Measurement of chronic pain in companion animals: Discussions from the Pain in Animals Workshop (PAW) 2017

In the face of increasing recognition and interest in treating chronic pain in companion animals, we struggle with a lack of therapeutic options. A significant barrier to the development of new therapeutics, or the critical evaluation of current therapies, is our inability to accurately measure chronic pain and its impact on companion animals. Over the last 20 years, much progress has been made in developing methods to measure chronic pain via subjective and objective methods - particularly in owner assessment tools and measurements of limb use and activity. Most work has been focused on chronic joint pain conditions, but there has been relatively little work in other areas of chronic pain, such as neuropathic and cancer pain. Although progress has been made, there is a considerable interest in improving our assessment of chronic pain, as evidenced by the multiple disciplines across industry, academia, and clinical practice from the veterinary and human medical fields that participated in the Pain in Animals Workshop held at the National Institutes of Health in 2017. This review is one product of that meeting and summarizes the current state of knowledge surrounding the measurement of chronic pain (musculoskeletal, cancer, neuropathic), and its impact, in cats and dogs.

Mechanical sensory threshold in Cavalier King Charles spaniels with syringomyelia-associated scratching and control dogs

It is assumed that Cavalier King Charles spaniels with Chiari-like malformation and syringomyelia experience central neuropathic pain. An association between spinal cord parenchymal lesions and specific clinical signs (e.g. spontaneous and evoked scratching, withdrawal, and paroxysmal pain manifestations with vocalisation) has been suggested. This led to the hypothesis that mechanical sensory threshold is altered in clinical cases. The aim of this study was to quantify the cervical mechanical sensory threshold using Semmes-Weinstein monofilaments in nine Cavalier King Charles spaniels with Chiari-like malformation and assumed syringomyelia-associated central neuropathic pain compared to eight control dogs. Clinical and neurological examination including magnetic resonance imaging was undertaken. Mean mechanical sensory threshold was not significantly different between case and control dogs (t-test on log10 transformed data; P=0.25). Substantial variation within and between dogs was seen, with individual thresholds ranging from 0.04 to 26g in case dogs and from 0.02 to 10g in control dogs. Based on these results, it is unlikely that Cavalier King Charles spaniels with Chiari-like malformation and syringomyelia have increased mechanical sensation characterised by lower mechanical sensory threshold when quantified with Semmes-Weinstein monofilaments. Whether clinical cases experience central neuropathic pain remains unknown. The assessment of sensory function in dogs with assumed central neuropathic pain should be multimodal and include not only mechanical but also tactile and thermal threshold quantification. The use of threshold quantification in a clinical setting is challenging due to an insufficient signal relative to the biological background noise within and between dogs.

Pain characterization and response to palliative care in dogs with naturally-occurring appendicular osteosarcoma: An open label clinical trial

This study aimed to characterize bone cancer pain (quantitative sensory testing (QST), stance asymmetry index, actimetry, scores of pain and quality of life (QoL)) in dogs with appendicular osteosarcoma (OSA), and to evaluate a stepwise palliative analgesic treatment.

The pain profile of thirteen client-owned dogs with OSA was compared with seven healthy dogs. Dogs with OSA were then enrolled in a prospective, open-label, clinical trial. Outcome measures included: primary and secondary mechanical thresholds (MT), conditioned pain modulation (CPM), stance asymmetry index, actimetry (most and least active periods), visual analog scales and QoL. After baseline assessments, stepwise treatment comprised orally administered cimicoxib (2 mg/kg q 24h), amitriptyline (1–1.5 mg/kg q 24h) and gabapentin (10 mg/kg q 8h); re-evaluations were performed after 14 (D14), 21 (D21) and 28 (D28) days, respectively. Statistics used mixed linear models (α = 5%; one-sided). Centralized nociceptive sensitivity (primary and secondary MT, and dynamic allodynia) was recorded in OSA dogs. Healthy dogs had responsive CPM, but CPM was deficient in OSA dogs. Construct validity was observed for the QST protocol. Asymmetry index was significantly present in OSA dogs. The CPM improved significantly at D14. When compared with baseline (log mean ± SD: 4.1 ± 0.04), most active actimetry significantly improved at D14 (4.3 ± 0.04), D21 and D28 (4.2 ± 0.04 for both). When compared with baseline, least active actimetry significantly decreased after treatment at all time-points indicating improvement in night-time restlessness. No other significant treatment effect was observed. Except for tactile threshold and actimetry, all outcomes worsened when gabapentin was added to cimicoxib-amitriptyline. Dogs with bone cancer are affected by widespread somatosensory sensitivity characterized by peripheral and central sensitization and have a deficient inhibitory system. This severe pain is mostly refractory to palliative analgesic treatment, and the latter was only detected by specific and sensitive outcomes.

Quantitative sensory testing in dogs with painful disease: A window to pain mechanisms?

Evaluation of the response to externally applied physical stimuli, such as pressure, heat, or cold is termed quantitative sensory testing (QST). QST may be used to identify and quantify alterations (gain or loss) in function of the sensory systems which detect and mediate these phenomena in both man and animals, and potentially discriminate peripheral and central sensitisation. It has been postulated that evaluation of QST parameters may predict response to analgesics, ultimately increasing the individualisation of treatment for pain. However, while there do appear to be correlations between QST measures and responses to analgesics in man, there is currently insufficient evidence to recommend QST to direct clinical treatments. The use of psychophysical testing, such as QST, in non-verbal subjects presents additional challenges, and requires familiarity with species and individual responses. This narrative review describes the investigations into QST in clinical populations of dogs to date, and discusses the potential benefits and limitations of such testing.

Investigation of sensory thresholds in Cavalier King Charles Spaniels with and without Chiari-like malformations and syringomyelia

Background

Cavalier King Charles Spaniels (CKCS) suffer pain associated with Chiari‐like malformation and syringomyelia (CMSM). People suffer from a similar condition and describe numerous sensory abnormalities. Sensory changes have not been quantified in affected CKCS.

Objectives

To use quantitative sensory testing (QST) to quantify thermal and mechanical thresholds in CKCS and to compare QST in dogs with and without syringomyelia (SM).

Animals

Forty‐four CKCS.

Methods

Prospective study. Dogs underwent neurological examinations and craniocervical magnetic resonance imaging (MRI). Thermal testing was performed over the humerus and thorax (n = 32); mechanical testing was performed on the paw and neck (n = 44). Latencies, thresholds, and response rates were compared with presence and severity of SM on MRI, presence of pain reported by the owner and pain identified on examination.

Results

Thirty dogs had SM, 30 were painful on examination, 29 were owner‐reported symptomatic. Thermal and mechanical variables were not significantly different based on presence or severity of SM. Dogs with pain on examination had decreased mechanical thresholds on the paw (0.38 kg, SD = 0.18) and neck (2.05 kg, SD = 0.74) compared to thresholds of dogs without pain on examination on the paw (0.60 kg, SD = 0.30) and neck (2.72 kg, SD = 0.57; P = .021).

Conclusions and Clinical Importance

Mechanical and thermal sensitivity does not appear to be related to the presence of SM, but mechanical sensitivity appears to be related to the presence of pain and clinical signs. Mechanical testing may be useful for assessing sensory abnormalities during clinical trials.

Acute pain and peripheral sensitization following cautery disbudding in 1- and 4-week-old calves

Acute pain and peripheral sensitization development after cautery disbudding was investigated in 33 calves administered preventive multimodal analgesia. The animals were assigned randomly to three groups: 1) Group SH (Control), undergoing sham disbudding at 1 and 4weeks of age; 2) Group ED (Early Disbudding), undergoing disbudding at 1week of age and sham disbudding at 4weeks of age; 3) Group LD (Late Disbudding), undergoing sham disbudding at 1week of age and disbudding at 4weeks of age. Physiological parameters (heart rate, respiratory rate, rectal temperature, invasive blood pressure, cortisol, β-endorphin, interleukin-1β, interleukin-6, tumor necrosis factor-α and haptoglobin plasmatic concentration), local variables (tactile sensitivity score, pressure pain thresholds and horn temperature), behavior and pain scores [multidimensional pain scale and visual analogue scale (VAS)] were assessed at baseline and at several pre-determined time points until 24h after disbudding. Tactile sensitivity score significantly and equally increased in both groups ED and LD and pressure pain thresholds significantly decreased in group LD until 24h after disbudding compared to group SH. Pain and VAS scores significantly and equally increased in both groups ED and LD until 24h after disbudding compared to group SH. No significant differences in physiological parameters, behavior and horn temperature were detected among groups. The present study suggests that acute pain and peripheral sensitization develop and do not differ in calves disbudded at 1week and 4weeks of age. Moreover, the use of physiological and behavioral parameters as sole indicators of acute pain might lead to improper conclusions and should be reassessed.