Neuropathic pain in dogs and cats: if only they could tell us if they hurt

How does chronic pain impact the lives of dogs: an investigation of factors that are associated with pain using the Animal Welfare Assessment Grid

Introduction

Chronic pain can profoundly affect the wellbeing of dogs and our understanding is limited regarding the multidimensional impact it has on dog quality of life. This study aimed to assess the factors that are significant and predictive of behavior problems in dogs using the Animal Welfare Assessment Grid (AWAG) to further understand what factors influence their welfare.

Methods

Seventy six AWAG assessments were undertaken across 46 dogs that clinicians diagnosed as having musculoskeletal conditions that caused chronic pain. Wilcoxon-rank sum tests were used to assess the difference in scores between dogs with behavior disorders and a cohort of healthy dogs (n = 143).

Results

All physical factors besides body condition, and all psychological, environmental, and procedural factors were significantly different between healthy dogs and dogs with chronic pain, evidencing how chronic pain impacts all domains of a dog's life. Spearman Rank Correlation Coefficient (RS) revealed several significant strong positive correlations such as the association between the severity of clinical symptoms with poorer mobility and the frequency at which the dog experienced fearful stimuli. Logistic regression showed that fears and anxieties frequency, the dog's reaction to stressors, engagement with enrichment, and social interactions were significant predictors of chronic pain in dogs.

Discussion

This highlights that typical signs of musculoskeletal disorders such as gait changes, stiffness, lameness might manifest after behavioral changes such as increased fearfulness, prolonged recovery from a stressful event, a reduced interested in social interactions, toys or play. Owners only seeking veterinary attention when the presence of physical signs of disease are evident may result in a delayed veterinary attention resulting in reduced welfare. Regular veterinary assessments combined with use of the AWAG can proactively identify these behavioral indicators and result in prompt treatment and improved quality of life.

SINGLE-DOSE, MULTIPLE-DOSE, AND THERAPEUTIC DRUG MONITORING PHARMACOKINETICS OF FIROCOXIB IN ASIAN ELEPHANTS (ELEPHAS MAXIMUS)

Firocoxib is a COX-2-selective nonsteroidal anti-inflammatory drug (NSAID) with limited effects on COX-1, which means it likely has fewer side effects than typically associated with other NSAIDs. This study determined possible doses of firocoxib based on single- and multidose pharmacokinetic trials conducted in 10 Asian elephants (Elephas maximus). Initially, two single oral dose trials (0.01 and 0.1 mg/kg) of a commercially available tablet (n = 6) and paste (n = 4) formulation were used to determine a preferred dose. The 0.1 mg/kg dose was further evaluated via IV single dose (n = 3) and oral multidose trials (tablets n = 6; paste n = 4). Serum peak and trough firocoxib concentrations were also evaluated in Asian elephants (n = 4) that had been being treated for a minimum of 90 consecutive days. Key pharmacokinetic parameters for the 0.1 mg/kg single-dose trials included mean peak serum concentrations of 49 ± 3.3 ng/ml for tablets and 62 ± 14.8 ng/ml for paste, area under the curve (AUC) of 1,332 ± 878 h*mg/ml for tablets and 1,455 ± 634 h*mg/ml for paste, and half-life (T1/2) of 34.3 ± 30.3 h for tablets and 19.9 ± 12.8 h for paste. After 8 d of dosing at 0.1 mg/kg every 24 h, pharmacokinetic parameters stabilized to an AUC of 6,341 ± 3,003 h*mg/ml for tablets and 5,613 ± 2,262 for paste, and T1/2 of 84.4 ± 32.2 h for tablets and 62.9 ± 2.3 h for paste. Serum COX inhibition was evaluated in vitro and ex vivo in untreated elephant plasma, where firocoxib demonstrated preferential inhibition of COX-2. No adverse effects from firocoxib administration were identified in this study. Results suggest administering firocoxib to Asian elephants at a dose of 0.1 mg/kg orally, using either tablet or paste formulations, every 24 h.

Cognitive Changes Associated with Aging and Physical Disease in Dogs and Cats

Behavior changes may indicate primary physical disease or primary behavioral disorders in veterinary patients. It is imperative to recognize that secondary behavioral problems can develop due to medical causes. The incidence of systemic disease increases with age and behavior manifestations can be similar to those expected with cognitive dysfunction syndrome. In this article, we review basic concepts of cognition, aging, and cognitive dysfunction syndrome. Additionally, we provide information regarding factors that influence cognition, and the role medical conditions have on the behavior of aging pets.

Case report: Neuropathic pain versus undesirable behavior in a Dachshund after hemilaminectomy surgery for an intervertebral disc extrusion

A 5.5 years-old male Dachshund was presented for evaluation because of undesirable behavior including barking, biting, sucking and licking the right-side flank, ventrally and slightly caudally to the level of the surgical incision 7 days after hemilaminectomy for a right-sided L1-2 intervertebral disc extrusion. The dog was being treated with oral gabapentin 10 mg/kg q8h. Repeat clinical examination on three occasions after post-operative discharge did not reveal any signs of hyperesthesia or neurological deficits and the behavior was not observed in the clinic during consultations. During a separate day of hospital admittance with the aim of evaluating for the presence or absence of the behavior, the dog also did not exhibit the behavior. Oral paracetamol 12 mg/kg q8h was added to medical treatment. When the dog was discharged and returned home, the behavior was immediately seen again. When the owners implemented verbal punishment, the behavior immediately ceased. The owner verbally corrected the dogs' behavior for two excitative days. Upon telephone consultation 3 days later, the owner reported that they only had observed three recurrences of the behavior that immediately ceased following verbal correction and did not recur thereafter. Oral analgesic medication was tapered and discontinued. No recurrence of the behavior was noticed during the next 2 months. The authors postulated the dog possibly expressed signs of neuropathic pain in the post-operative period, or that the behavior was of a "compulsive disorder-like" nature as it only occurred when the dog was at home and in the presence of the owner. The eventual outcome and result of verbal corrections implemented by the owner seem to support the latter. In conclusion, compulsive-like undesirable behavior should be considered a differential diagnosis in dogs in the post-operative period of procedures possibly associated with the development or expression of signs of neuropathic pain.

Periodontal disease in cats under primary veterinary care in the UK: frequency and risk factors

OBJECTIVES

Periodontal disease is a multifactorial inflammatory disease that can have major welfare implications in cats. This study aimed to report the frequency and demographic risk factors of periodontal disease and to explore associations with common comorbid disorders in cats in the UK.

METHODS

The study included a random sample of 18,249 cats obtained from 1,255,130 cats under primary care during 2019 from clinics participating in the VetCompass programme. All disorders recorded during 2019 were extracted and reported. Risk factor and comorbid disorder analysis used multivariable logistic regression modelling.

RESULTS

Periodontal disease had a 1-year period prevalence of 15.2% (95% confidence interval [CI] 14.72-15.76). Breeds with the highest prevalence included Siamese (18.7%, 95% CI 12.24-26.72) and Maine Coon (16.7%, 95% CI 11.37-23.18). The median age of cats with periodontal disease (9.47 years, interquartile range [IQR] 5.96-12.97) was higher than for cats without periodontal disease (4.94 years, IQR 1.95-9.51; P <0.001). Increasing adult body weight, increasing age and sex-neuter status were significantly associated with rising odds of periodontal disease. Cats with periodontal disease had a higher median count of comorbid disorders per individual cat (3, IQR 2-4, range 1-14) than cats without periodontal disease (1, IQR 0-2, range 0-15; P <0.001). Cats with periodontal disease had 1.79 times the odds (95% CI 1.62-1.99, P <0.001) of diagnosis with at least one comorbid disorder disease than cats without periodontal disease.

CONCLUSIONS AND RELEVANCE

Periodontal disease is the most common specific diagnosis in cats and is confirmed as a leading health issue in cats. Ageing is identified as the strongest predictor of periodontal disease risk in cats, suggesting the potential for increasing health gains from emphasis on dental care and health in cats as they age. The study offers evidence on a close link between periodontal disease and reduced overall health in cats.

Analgesic, cardiorespiratory effects and motor block characteristics of epidural levobupivacaine alone or in combination with methadone or dexmedetomidine in bitches undergoing unilateral total mastectomy

The aim of this study was to evaluate the latency, extent of analgesia, and duration of motor block of levobupivacaine alone and combined with methadone or dexmedetomidine after epidural administration during and after mastectomy in dogs. Twenty-four mature, mixed-breed female dogs were randomly divided into three experimental groups with eight animals each, according to the agents used in lumbosacral epidural analgesia: levobupivacaine 0.75% alone (1.5mg/kg - control group), levobupivacaine 0.75% (1.5 mg/kg) + methadone 1% (0.3 mg/kg), or levobupivacaine 0.75% (1.5 mg/kg) + dexmedetomidine 0.05% (3 µg/kg). During surgery, cardiorespiratory parameters were evaluated. Rescue analgesia was given when there were signs of nociception and was necessary in all three treatment groups. Since all animals received rescue analgesia during the surgery and immediately post-surgery, the duration of the sensitive block were not evaluated. The extent of sensory block was between the 12º and 13º thoracic vertebrae for the control group, 7º thoracic vertebra to 5º lumbar vertebra (methadone group), and 8º thoracic vertebra to 4º lumbar vertebra for the dexmedetomidine group. Methadone or dexmedetomidine combined with levobupivacaine increased the extent of the sensory block and the duration of the motor block in bitches when administered via the epidural route.

Thoracolumbar retrolaminar block in seven dogs undergoing spinal surgery

Background

Thoracolumbar intervertebral disc extrusion is a common neurologic complaint in dogs and is associated with debilitating pain that requires careful analgesic management to avoid the transition to a chronic pain state. Recently, there has been an increased effort to incorporate regional anaesthetic techniques whenever possible, both for perioperative analgesia management and for prevention of chronic pain. A novel regional anaesthetic technique named retrolaminar block is a fascial plane block where the local anaesthetic is injected directly on top of the dorsal aspect of the vertebral lamina, in the fascial plane between the lamina and the epaxial muscles. The technique was recently described in humans and it is claimed to provide analgesia in patients undergoing thoracic and lumbar procedures. To the authors’ knowledge, the retrolaminar block has not been previously reported in live dogs.

Case presentation

Seven dogs presented to our hospital for suspected thoracolumbar intervertebral disc extrusion were anaesthetised using an anaesthetic premedication and induction protocol tailored for each individual animal. Once the suspected diagnosis was confirmed, all seven dogs were placed in sternal recumbency, and the target thoracolumbar vertebral spinous process was identified with palpation. A unilateral retrolaminar block was performed in all dogs with 2 mg/kg of 0.25% bupivacaine. Physiologic parameters, as well as responses to nociceptive stimuli, were monitored throughout the anaesthetic event.

Intraoperatively, one dog required a bolus of fentanyl to control nociceptive stimulation while the epaxial muscles were retracted. No further intraoperative rescue analgesia was required in any of the cases. The postoperative pain was assessed using the Short Form of Glasgow Composite Measure Pain Scale for dogs every four hours for the duration of the dogs’ hospitalization. The retrolaminar block reduced the intraoperative requirement for systemic opioids and other adjunct analgesic agents and all dogs were comfortable throughout their hospitalization and up until the time of their discharge.

Conclusions

This case report presents the performance of the retrolaminar block technique as part of multimodal analgesia management in seven dogs undergoing thoracolumbar spinal surgery.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13620-022-00224-7.

Effect of Methadone or Hydromorphone on Cardiac Conductivity in Dogs Before and During Sevoflurane Anesthesia

Objective: To evaluate changes in electrocardiogram (ECG) variables in healthy dogs receiving either methadone or hydromorphone IV before and during sevoflurane anesthesia.

Study Design: Prospective clinical study.

Animals: Forty client-owned dogs.

Methods: Dogs were randomized to receive methadone 0.5 mg/kg IV or hydromorphone 0.1 mg/kg IV in each part of a two-part study. In part one, dogs received the opioid prior to sevoflurane anesthesia (groups MS, n = 12 and HS, n = 12). Anesthesia was induced with propofol IV, maintained with sevoflurane, and dogs were mechanically ventilated. Standard 6-lead ECG recordings were obtained before opioid administration, 2, 5, and 10 min after opioid administration prior to anesthesia, and during anesthesia 15 min after end-tidal sevoflurane stabilized at 2.4%. In part two, conscious dogs received the same opioid treatments and ECGs were obtained at equivalent time points without undergoing anesthesia (groups M, n = 8 and H, n = 8). Values for ECG variables were determined by a blinded cardiologist and included: Heart rate (HR), PR interval, QT interval, and HR corrected QT interval (QT_c) using the Bazett (QT_cB), Fridericia (QT_cF), and Van de Water (QT_cV) formulas. Differences over time and between all four groups were evaluated using ANOVA for repeated measures with significance set at p ≤ 0.05.

Results: Both methadone and hydromorphone administration reduced HR and prolonged PR and QT intervals, with greater changes observed during sevoflurane anesthesia. The greatest prolongation in QT interval was observed in dogs administered methadone during sevoflurane anesthesia.

Conclusions and Clinical Relevance: Methadone and hydromorphone caused disturbances in myocardial electrical activity, and the addition of sevoflurane enhanced these disturbances. Both drugs caused considerable QT interval prolongation into the proarrhythmogenic range, with methadone causing greater prolongation.

Feline Neuropathic Pain

Neuropathic pain represents the extreme in maladaptive pain processing. In itself, it is a disease in which pain has become exaggerated in some combination of scope, severity, character, field, duration, and spontaneity. It is almost certainly an underappreciated, underdiagnosed cause of possible significant patient morbidity in cats. This article explores the basic mechanisms, recognition, known and suspect syndromes, and prospective treatment of feline maladaptive and neuropathic pain.

Behavior as an Illness Indicator

When an owner notices a behavior change in their cat that concerns them enough to present the cat to the vet, there are 3 possibilities: the behavior change reflects a change in behavioral health (a change in psychological state), a change in medical health (a change in physical state), or a combination (comorbid medical and behavioral pathologies). Because many behavioral pathologies are diagnoses of exclusion, it is important that the veterinarian rule out all of the likely medical differentials for the changed behavior. This article is a behavior-by-behavior guide to the more common differentials for the most common problem behaviors.

Canine Degenerative Lumbosacral Stenosis: Prevalence, Impact And Management Strategies

Canine degenerative lumbosacral stenosis (DLSS) is a syndrome of low back pain with or without neurologic dysfunction associated with compression of the cauda equina. Most commonly occurring in medium- to large-breed dogs of middle to older age, German shepherd and working dogs are predisposed. Diagnosis is based on a combination of clinical signs, advanced imaging and ruling out other differential diagnoses. The volume of the intervertebral foramina at the lumbosacral junction is naturally reduced on extension but degenerative changes lead to a more marked reduction that can impinge the L7 nerve roots. Evidence is lacking on which to base decision-making for treatment of dogs with DLSS. However, surgical intervention may be indicated in dogs that do not respond to conservative management, or for dogs in which there is a requirement to work that prevents lifestyle adjustments. Improvements in electrodiagnosis and novel intra-discal treatments may improve the management of DLSS in the future.

Pregabalin alleviates clinical signs of syringomyelia-related central neuropathic pain in Cavalier King Charles Spaniel dogs: a randomized controlled trial

OBJECTIVE

We aimed to assess the efficacy and benefit-risk profile of pregabalin (PGN) to reduce the clinical signs of central neuropathic pain (CNeP) as reflected by scratching episodes in dogs with symptomatic syringomyelia (SM).

STUDY DESIGN

Randomized, double-blind, placebo-controlled crossover study.

ANIMALS

A total of 12 client-owned Cavalier King Charles Spaniels (age, 1.1-7.4 years, bodyweight, 8.2-10.8 kg) with magnetic resonance imaging-confirmed SM and clinical signs of CNeP.

METHODS

Dogs were randomized to either PGN 150 mg or placebo for 25 days, followed by 48 hour washout period before crossover to the alternate phase of 25 days. The primary outcome was defined as number of scratching events during 10 minutes of video-recorded physical activity. Treatment effect was estimated using a generalized estimation equation model. Benefit-risk and quality of life assessments were obtained through owner interviews focusing on potential adverse events.

RESULTS

The treatment effect estimate was an 84% (95% confidence interval = 75-89%) reduction in mean number of scratching events relative to baseline compared with placebo (p < 0.0001). Owner-assessed satisfactory quality of life was status quo and rated as 'good' or 'could not be better' in six/11 dogs and improved in four/11 dogs. The most prevalent adverse events were increased appetite in nine/12 dogs and transient ataxia in nine/12 dogs. There was one dog withdrawn by the owner 7 days after crossover to PGN owing to persistent ataxia. No dogs needed rescue analgesia during the trial.

CONCLUSIONS AND CLINICAL RELEVANCE

PGN is superior to placebo in the reduction of clinical signs of SM-related CNeP in dogs. At a dose range of 13-19 mg kg^-1 orally twice daily, the encountered adverse events were acceptable to all but one owner.

A preoperative bupivacaine retrobulbar block offers superior antinociception compared with an intraoperative splash block in dogs undergoing enucleation

PURPOSE

Investigate nociception differences in dogs undergoing enucleation administered bupivacaine either via preoperative retrobulbar block (pRB) or intraoperative splash block (iSB).

METHODS

Prospective, randomized, double-masked, clinical comparison study. Dogs undergoing unilateral enucleation were randomized to two groups: one received bupivacaine pRB and saline iSB of the same volume, and the other received saline pRB and bupivacaine iSB. The following intraoperative parameters were recorded: heart rate (HR), respiratory rate (RR), end-tidal CO₂ (EtCO₂ ); systolic, mean, and diastolic arterial blood pressure (SAP, MAP, and DAP respectively); inspired end-tidal isoflurane concentration (EtISOIns), and expired end-tidal isoflurane concentration (EtISOExp). Pain scores were recorded pre- and postoperatively. Analgesic rescue was documented. Surgical hemorrhage and postoperative bruising and swelling were graded subjectively by the surgeon (HDW) and study coordinator (AEZ).

RESULTS

A significant (P = .0399) increase from baseline in overall mean heart rate was recorded in iSB bupivacaine patients (n = 11) compared with pRB bupivacaine patients (n = 11), with no significant differences in other intraoperative physiologic parameters, or pain scores. More analgesic rescue events occurred in iSB bupivacaine patients compared to pRB bupivacaine patients. A near-significant increase in intraoperative bleeding (P = .0519), and a significant increase in bruising (P = .0382) and swelling (P = .0223) was noted in the iSB bupivacaine group.

CONCLUSIONS

Preoperative retrobulbar block bupivacaine is more effective than an iSB bupivacaine at controlling both intraoperative and postoperative nociception in dogs undergoing enucleation. Additionally, iSB causes more postoperative bruising and swelling and may be associated with increased intraoperative hemorrhage.

Multimodal analgesia for treatment of allodynia and hyperalgesia after major trauma in a cat

Case summary

A 2-year-old polytraumatized male cat was admitted to a teaching hospital for correction of a defective inguinal herniorrhaphy. Upon arrival, the cat showed signs of neuropathic pain, including allodynia and hyperalgesia. Analgesic therapy was initiated with methadone and metamizole; however, 24 h later, the signs of pain continued. Reparative surgery was performed, and a multimodal analgesic regimen was administered (methadone, ketamine, wound catheter and epidural anesthesia). Postoperatively, the cat showed signs of severe pain, assessed using the UNESP-Botucatu multidimensional composite pain scale. Rescue analgesia was initiated, which included methadone, bupivacaine (subcutaneous wound-diffusion catheter) and transversus abdominis plane block. Because the response was incomplete, co-adjuvant therapy (pregabalin and electroacupuncture) was then implemented. Fourteen days after admission, the patient was discharged with oral tramadol and pregabalin for at-home treatment.

Relevance and novel information

Neuropathic pain is caused by a primary lesion or dysfunction in the nervous system and is a well-described complication following trauma, surgical procedures such as hernia repair, and inadequate analgesia. The aims of this report are to: (1) describe a presentation of neuropathic pain to highlight the recognition of clinical signs such as allodynia and hyperalgesia in cats; and (2) describe treatment of multi-origin, severe, long-standing, ‘mixed’ pain (acute inflammatory with a neuropathic component). The patient was managed using multiple analgesic strategies (multimodal analgesia), including opioids, non-steroidal anti-inflammatory drugs, locoregional anesthesia, co-adjuvant drugs and non-pharmacological therapy (electroacupuncture).

Feline hyperaesthesia syndrome with self-trauma to the tail: retrospective study of seven cases and proposal for an integrated multidisciplinary diagnostic approach

CASE SERIES SUMMARY

This was a retrospective study on the clinical features and response to treatment in seven cats with feline hyperaesthesia syndrome (FHS) and tail mutilation. FHS is a poorly understood disorder characterised by skin rippling over the dorsal lumbar area, episodes of jumping and running, excessive vocalisation, and tail chasing and self-trauma. The majority of the cats were young, with a median age of 1 year at the onset of clinical signs, male (n = 6) and with access to the outdoors (n = 5). Multiple daily episodes of tail chasing and self-trauma were reported in five cats, with tail mutilation in four cats. Vocalisation during the episodes (n = 5) and rippling of lumbar skin (n = 5) were also reported. Haematology, serum biochemistry, Toxoplasma gondii and feline immunodeficiency virus/feline leukaemia virus serology, MRI scans of brain, spinal cord and cauda equina, cerebrospinal fluid analysis and electrodiagnostic tests did not reveal any clinically significant abnormalities. A definitive final diagnosis was not reached in any of the cats, but hypersensitivity dermatitis was suspected in two cases. A variety of medications was used alone or in combination, including gabapentin (n = 6), meloxicam (n = 4), antibiotics (n = 4), phenobarbital (n = 2), prednisolone (n = 2) and topiramate (n = 2); ciclosporin, clomipramine, fluoxetine, amitriptyline and tramadol were used in one cat each. Clinical improvement was achieved in six cases; in five cats complete remission of clinical signs was achieved with gabapentin alone (n = 2), a combination of gabapentin/ciclosporin/amitriptyline (n = 1), gabapentin/prednisolone/phenobarbital (n = 1) or gabapentin/topiramate/meloxicam (n = 1).

RELEVANCE AND NOVEL INFORMATION

This is the first retrospective study on a series of cats with FHS. The diagnostic work-up did not reveal any significant abnormalities of the central or peripheral nervous system; dermatological and behavioural problems could not be ruled out. We propose an integrated multidisciplinary diagnostic pathway to be used for the management of clinical cases and for future prospective studies.

Refinement of the Montreal Instrument for Cat Arthritis Testing, for Use by Veterinarians: detection of naturally occurring osteoarthritis in laboratory cats

Objectives Feline osteoarthritis causes pain and disability. Detection and measurement is challenging, relying heavily on owner report. This study describes refinement of the Montreal Instrument for Cat Arthritis Testing, for Use by Veterinarians. Methods A video analysis of osteoarthritic (n = 6) and non-osteoarthritic (n = 4) cats facilitated expansion of scale items. Three successive therapeutic trials (using gabapentin, tramadol and oral transmucosal meloxicam spray) in laboratory cats with and without natural osteoarthritis (n = 12-20) permitted construct validation (assessments of disease status sensitivity and therapeutic responsiveness) and further scale refinements based on performance. Results Scale osteoarthritic sensitivity improved from phase I to phase III; phase III scale total score ( P = 0.0001) and 4/5 subcategories - body posture ( P = 0.0006), gait ( P = 0.0031), jumping (0.0824) and global distance examination ( P = 0.0001) - detected osteoarthritic cats. Total score inter-rater (intra-class correlation coefficients [ICC] = 0.64-0.75), intra-rater (ICC = 0.90-0.91) and overall internal consistency (Cronbach's alpha = 0.85) reliability were good to excellent. von Frey anesthesiometer-induced paw withdrawal threshold increased with gabapentin in phase I, in osteoarthritic cats ( P <0.001) but not in non-osteoarthritic cats ( P = 0.075). Night-time activity increased during gabapentin treatment. Objective measures also detected tramadol and/or meloxicam treatment effects in osteoarthritic cats in phases II and III. There was some treatment responsiveness: in phase I, 3/10 subcategory scores improved ( P <0.09) in treated osteoarthritic cats; in phase II, 3/8 subcategories improved; and in phase III, 1/5 subcategories improved ( P <0.096). Conclusions and relevance The revised scale detected naturally occurring osteoarthritis, but not treatment effects, in laboratory cats, suggesting future potential for screening of at-risk cats. Further study is needed to confirm reliability, validity (disease sensitivity and treatment responsiveness) and clinical feasibility, as well as cut-off scores for osteoarthritic vs non-osteoarthritic status, in client-owned cats.

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

OBJECTIVE

To study the feasibility and test-retest repeatability of a sensory threshold examination protocol (STEP) and report the quantitative sensory threshold distributions in healthy dogs.

STUDY DESIGN

Prospective, observational, cohort study.

ANIMALS

Twenty-five healthy client-owned dogs.

METHODS

Tactile sensitivity test (TST) (von Frey filaments), mechanical thresholds (MT with 2, 4 and 8 mm probes), heat thresholds (HT) and responsiveness to cold stimulus (CT at 0 °C) were quantitatively assessed for five body areas (BAs; tibias, humeri, neck, thoracolumbar region and abdomen) in a randomized order on three different occasions. Linear mixed model and generalized linear mixed models were used to evaluate the effects of body weight category, age, sex, BA, occasion, feasibility score and investigator experience. Test-retest repeatability was evaluated with the intra-class correlation coefficient.

RESULTS

The STEP lasted 90 minutes without side effects. The BA affected most tests (p ≤ 0.001). Higher thresholds and longer cold latencies were scored in the neck (p ≤ 0.024) compared to other BAs. Weight category affected all thresholds (p ≤ 0.037). Small dogs had lower MT (∼1.4 N mean difference) and HT (1.1 °C mean difference) than other dogs (p ≤ 0.029). Young dogs had higher HT than adults (2.2 °C mean difference) (p = 0.035). Gender also affected TST, MT and HT (p < 0.05) (females versus males: TST odds ratio = 0.5, MT = 1.3 N mean difference, HT = 2.2 °C mean difference). Repeatability was substantial to moderate for all tests, but poor for TST. There was no difference in thresholds between occasions, except for CT. Test-retest repeatability was slightly better with the 2 mm MT probe compared to other diameters and improved with operator experience.

CONCLUSIONS AND CLINICAL RELEVANCE

The STEP was feasible, was well tolerated and showed substantial test-retest repeatability in healthy dogs. Further validation is needed in dogs suffering pain.

Evaluation of an ultrasound-guided technique for axillary brachial plexus blockade in cats

Objectives

The aim of this study was to evaluate and refine an ultrasound (US)-guided technique to block the brachial plexus (BP) at the level of the axillary space in live cats.

Methods

Eight adult experimental cats were enrolled into the study. The animals were sedated and positioned in dorsal recumbency with the limb to be blocked abducted 90º. The US transducer was placed in the axillary region and a non-traumatic peripheral nerve block needle was inserted in-plane with respect to the transducer, medial to the BP up to the level of the axillary artery. Lidocaine 1% (0.4 ml/kg) was injected as the needle was being progressively withdrawn in a caudal-to-cranial direction. The efficacy of the block was confirmed by evaluation of the motor and sensory functions of the blocked forelimb. Motor blockade was assessed observing the position of the blocked leg on standing and walking patterns. Sensory blockade was evaluated by the stimulation of mechanical nociceptors in the dermatomes supplied by the four major sensory nerves of the distal thoracic limb.

Results

The BP was successfully located by US in all cases. The achieved BP block was complete in six cats (75%) and partial in the remaining two cats (25%). All animals recovered uneventfully from the sedation and the BP blocks.

Conclusions and relevance

The US-guided block at the axillary space evaluated in this study is a feasible, reproducible and safe technique to block the BP plexus in experimental live cats.

Femoral nerve entrapment in a dog with diffuse idiopathic skeletal hyperostosis

OBJECTIVE

To report femoral neuropathy caused by nerve entrapment associated with diffuse idiopathic skeletal hyperostosis (DISH).

STUDY DESIGN

Case report.

ANIMAL

Seven-year-old female spayed Boxer dog.

RESULTS

Entrapment of the right femoral nerve due to DISH caused a femoral nerve deficit and atrophy of muscle groups associated with the affected nerve. A combination of computed tomography and magnetic resonance imaging was performed to provide a diagnosis. Amputation of the right transverse process of the sixth lumbar vertebra at the level of nerve entrapment relieved the neurological abnormality.

CONCLUSIONS

Nerve entrapment leading to neurapraxia may occur concurrently with DISH and surgery in this case was successful in restoring function.

CLINICAL RELEVANCE

Peripheral neuropathy from nerve entrapment should be considered in patients with DISH. Surgical amputation of impinging osseous structures may be indicated for relief of femoral neuropathy.

Veterinarians' attitudes to chronic pain in dogs

Veterinary surgeons in the UK were invited to complete an internet survey concerning their attitudes to chronic pain in dogs. UK veterinary surgeons numbering 215 completed surveys in full along with 48 worldwide specialists in anaesthesia and 37 worldwide specialists in oncology. Osteoarthritis, dental and aural disease, vertebral and spinal cord conditions, neoplasia and skin conditions were considered important causes of chronic pain in dogs. UK practitioners used significantly fewer classes of analgesic drugs regularly than either category of specialist. The major barriers to adequate treatment of chronic pain were reported as difficulties with pain assessment, expense of drugs, and difficulties with owner compliance. Illustrations of six common neoplastic conditions were used and scored for pain according to prior experience by practitioners. All six conditions were consistently described as involving some degree of pain with primary bone tumour and oral tumour, causing severe pain and moderate to severe pain, respectively. Years since graduation and specialist status affected the pain scores attributed to the conditions. There was a significant correlation between the pain score attributed to the illustrated condition, and the tendency to administer analgesia.

Characterisation of tramadol, morphine and tapentadol in an acute pain model in Beagle dogs

OBJECTIVE

To evaluate the analgesic potential of the centrally acting analgesics tramadol, morphine and the novel analgesic tapentadol in a pre-clinical research model of acute nociceptive pain, the tail-flick model in dogs.

STUDY DESIGN

Prospective part-randomized pre-clinical research trial.

ANIMALS

Fifteen male Beagle dogs (HsdCpb:DOBE), aged 12-15 months.

METHODS

On different occasions separated by at least 1 week, dogs received intravenous (IV) administrations of tramadol (6.81, 10.0 mg kg(-1) ), tapentadol (2.15, 4.64, 6.81 mg kg(-1) ) or morphine (0.464, 0.681, 1.0 mg kg(-1) ) with subsequent measurement of tail withdrawal latencies from a thermal stimulus (for each treatment n = 5). Blood samples were collected immediately after the pharmacodynamic measurements of tramadol to determine pharmacokinetics and the active metabolite O-demethyltramadol (M1).

RESULTS

Tapentadol and morphine induced dose-dependent antinociception with ED50-values of 4.3 mg kg(-1) and 0.71 mg kg(-1) , respectively. In contrast, tramadol did not induce antinociception at any dose tested. Measurements of the serum levels of tramadol and the M1 metabolite revealed only marginal amounts of the M1 metabolite, which explains the absence of the antinociceptive effect of tramadol in this experimental pain model in dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Different breeds of dogs might not or only poorly respond to treatment with tramadol due to low metabolism of the drug. Tapentadol and morphine which act directly on μ-opioid receptors without the need for metabolic activation are demonstrated to induce potent antinociception in the experimental model used and should also provide a reliable pain management in the clinical situation. The non-opioid mechanisms of tramadol do not provide antinociception in this experimental setting. This contrasts to many clinical situations described in the literature, where tramadol appears to provide useful analgesia in dogs for post-operative pain relief and in more chronically pain states.

Therapeutic options for the treatment of chronic pain in dogs

Chronic pain is a widely recognised problem in humans and is being increasingly recognised as a significant problem in dogs. Whilst a large number of therapies are described and utilised to treat chronic pain in dogs, there is a severe shortage of evidence to guide practitioners in selection of treatments. Until more evidence becomes available, practitioners should adopt a cautious approach, utilising licensed treatments first when possible. Non-pharmacological therapies should be incorporated into the chronic pain management plan whenever possible. Given the probable prevalence of chronic pain in dogs there is an urgent need for research to identify effective treatments.

Institutional animal care and use committee considerations for animal models of peripheral neuropathy

Peripheral neuropathy and neuropathic pain are debilitating, life-altering conditions that affect a significant proportion of the human population. Animal models, used to study basic disease mechanisms and treatment modalities, are diverse and provide many challenges for institutional animal care and use committee (IACUC) review and postapproval monitoring. Items to consider include regulatory and ethical imperatives in animal models that may be designed to study pain, the basic mechanism of neurodegeneration, and different disease processes for which neuropathic pain is a side effect. Neuropathic pain can be difficult to detect or quantify in many models, and pain management is often unsuccessful in both humans and animals, inspiring the need for more research. Design of humane endpoints requires clear communication of potential adverse outcomes and solutions. Communication with the IACUC, researchers, and veterinary staff is also key for successful postapproval monitoring of these challenging models.

Far lateral lumbar disc extrusion: MRI findings and surgical treatment

This case report describes the magnetic resonance imaging (MRI) findings and the treatment of a far lateral extrusion of disc material at the sixth and seventh lumbar vertebrae (L6-L7) in a five-year-old male Alpine Dachsbracke dog referred to our hospital for investigation of the complaint of a one week progressive lameness in the left pelvic limb and poorly localized back pain. An extra-foraminal left lateral disc herniation impinging on the sixth lumbar nerve root was diagnosed by MRI examinations. Due to the far lateral position of the extruded disc material on MRI, surgical opening of the spinal canal was not necessary. Removal of the herniated soft disc material impinging on the L6 nerve root, and fenestration of the L6-L7 disc was performed laterally. To the author's knowledge 'far-lateral' disc herniation beyond the neuroforamen without any spinal canal contact has not been described in dogs until now. A complete recovery with no evidence of pain was achieved only after a couple of weeks after surgery. We acknowledge that it is possible that other pathological mechanisms may have contributed to clinical signs and to a delayed recovery.

Where do we go from here? Future treatment strategies for chronic pain

Many of the tools that can be used to alleviate chronic pain in our patients are readily available to all practitioners, but they are not used with appropriate frequency. Thus, the immediate future of chronic pain therapy is simply to do more of what we are already doing. There are also drugs and techniques currently used in human medicine that may be available to us in the near future and many drugs and techniques on the research bench that might make it to our patients in the more distant future. Because of the magnitude of the chronic pain problem in human medicine, research on the treatment of chronic pain is intense, and the hope is that both human and veterinary patients will eventually benefit.

Diagnosis and treatment of osteoarthritis

Osteoarthritis (OA) is a common disease in aging dogs and cats but frequently goes undiagnosed and untreated. Although OA cannot be cured, long-term management of the disease can be very rewarding for the veterinary medical team as well as pet owners. Managing pain with pain medications is an essential first step. There are a wealth of pain medications available, including nonsteroidal antiinflammatory drugs, gabapentin, amantadine, and tramadol. There are also physical modalities available for pain reduction. Weight management and nutritional joint support are also important in aspects of managing OA in dogs and cats. Finally, physical rehabilitation is a great way to improve mobility and keep pets active as they age.

Chronic pain: pathophysiology and treatment implications

An examination of the current understanding of the processes and related therapies aimed at treatment of chronic pain in animals is presented. Discussion focuses on mechanisms involved in the neural pathways of chronic pain, differences between acute and chronic pain, and pharmacologic options for chronic pain as they relate to inflammatory, neoplastic, and neuropathic processes.

Chronic neuropathic pain in veterinary patients

Neuropathic pain is pathophysiologically distinct from other types of chronic pain and is defined by the Neuropathic Pain Special Interest Group of the International Association for the Study of Pain as "pain arising as a direct consequence of a lesion or disease affecting the somatosensory system." At least in humans, and perhaps in animals, neuropathic pain causes a much greater impairment in the patient's quality of life than is caused by other pain syndromes. And, unfortunately, this type of pain is generally quite difficult to accurately diagnose and even harder to effectively treat. A brief review of neuropathic pain and its treatment in veterinary patients is presented here.

Feline orofacial pain syndrome (FOPS): a retrospective study of 113 cases

Feline orofacial pain syndrome (FOPS) is a pain disorder of cats with behavioural signs of oral discomfort and tongue mutilation. This report describes the findings from a case series of 113 cats including 100 Burmese. FOPS is suspected to be a neuropathic pain disorder and the predominance within the Burmese cat breed suggests an inherited disorder, possibly involving central and/or ganglion processing of sensory trigeminal information. The disease is characterised by an episodic, typically unilateral, discomfort with pain-free intervals. The discomfort is triggered, in many cases, by mouth movements. The disease is often recurrent and with time may become unremitting - 12% of cases in this series were euthanased as a consequence of the condition. Sensitisation of trigeminal nerve endings as a consequence of oral disease or tooth eruption appears to be an important factor in the aetiology - 63% of cases had a history of oral lesions and at least 16% experienced their first sign of discomfort during eruption of permanent teeth. External factors can also influence the disease as FOPS events could be directly linked to a situation causing anxiety in 20% of cats. FOPS can be resistant to traditional analgesics and in some cases successful management required anti-convulsants with an analgesic effect.