Corticosteroid-associated laminitis

Equine allergic skin diseases: Clinical consensus guidelines of the World Association for Veterinary Dermatology

BACKGROUND

Allergic skin diseases are common in horses worldwide. The most common causes are insect bites and environmental allergens.

OBJECTIVES

To review the current literature and provide consensus on pathogenesis, diagnosis, treatment and prevention.

MATERIALS AND METHODS

The authors reviewed the literature up to November 2022. Results were presented at North America Veterinary Dermatology Forum (2021) and European Veterinary Dermatology Congress (2021). The report was available to member organisations of the World Association for Veterinary Dermatology for feedback.

CONCLUSIONS AND CLINICAL RELEVANCE

Insect bite hypersensitivity (IBH) is the best characterised allergic skin disease. An immunoglobulin (Ig)E response against Culicoides salivary antigens is widely documented. Genetics and environmental factors play important roles. Tests with high sensitivity and specificity are lacking, and diagnosis of IBH is based on clinical signs, seasonality and response to insect control. Eosinophils, interleukin (IL)-5 and IL-31 are explored as therapeutic targets. Presently, the most effective treatment is insect avoidance. Existing evidence does not support allergen-specific immunotherapy (ASIT) using commercially available extracts of Culicoides. Hypersensitivity to environmental allergens (atopic dermatitis) is the next most common allergy. A role for IgE is supported by serological investigation, skin test studies and positive response to ASIT. Prospective, controlled, randomised studies are limited, and treatment relies largely on glucocorticoids, antihistamines and ASIT based on retrospective studies. Foods are known triggers for urticaria, yet their role in pruritic dermatitis is unknown. Recurrent urticaria is common in horses, yet our understanding is limited and focussed on IgE and T-helper 2 cell response. Prospective, controlled studies on treatments for urticaria are lacking. Glucocorticoids and antihistamines are primary reported treatments.

Pharmacokinetics of diphenhydramine following single-dose intravenous and oral administration in non-fasted adult horses

Diphenhydramine is an H1 receptor antagonist used to control urticaria and other allergic signs caused by type I hypersensitivity reactions in horses (Equus caballus). Limited studies have been conducted on pharmacokinetics of this drug in horses, with no studies involving oral formulations. Our study investigated pharmacokinetics of an oral diphenhydramine formulation compared to intravenous administration in non-fasted adult horses. Six healthy horses underwent a single administration of three different doses of diphenhydramine (1 mg/kg intravenously, 1 mg/kg intragastrically, and 5 mg/kg intragastrically) with a two-week washout period between doses. Bioavailability of intragastric diphenhydramine was less than one percent and six percent for 1 mg/kg and 5 mg/kg intragastric doses, respectively. This poor bioavailability is similar to what is reported in dogs. Two of six horses experienced transient side effects after intravenous diphenhydramine administration, emphasizing the need for determining therapeutic plasma levels in efforts to determine the lowest effective dose minimizing risk of adverse effects. The main conclusion of our study was that oral diphenhydramine at doses up to 5 mg/kg are unlikely to achieve therapeutic plasma levels in adult horses.

Glucocorticoid treatment in horses with asthma: A narrative review

Despite substantial research efforts to improve the treatment and outcome of horses with asthma, glucocorticoids (GC) remain the cornerstone of drug treatment of this prevalent disease. The high efficacy of GC to relieve airway obstruction explains their extensive use despite potential deleterious effects. However, much is yet to be uncovered concerning GC use in horses with asthma, including the comparative efficacy of the different drugs, the determination of minimal effective doses and the mechanisms underlying their variable modulation of airway inflammation. The objectives of this structured review were to report and compare the plethora of effects of the various GC used in asthmatic horses with a focus on impact on lung function, airway inflammation, and bronchial remodeling. Adverse effects are also briefly described, with an emphasis on those that have been specifically reported in horses with asthma. Ultimately, we aimed to highlight gaps in the literature and to identify future research areas.

[Therapy of bullous pemphigoid in a Warmblood gelding]

A 15-year-old Warmblood gelding was presented with multiple large, ulcerative, and crusty dermal lesions that had been existing for 4 years. Histopathology of a skin biopsy revealed cleft formation at the dermal-epidermal junction beneath the basal cells and above the basement membrane leading to the diagnosis of bullous pemphigoid. Immunosuppressive therapy with dexamethasone and azathioprine was initiated and after 14 weeks full remission of the ulcers was achieved. Scar tissue formation was evident in the areas of the formerly affected lesions. Following medication tapering over a period of 5 months, long-term therapy was continued with a maintenance dose of 0.5 mg/kg azathioprine daily. The ulcerative lesions recurred after 63 weeks of disease stabilization. Additionally, adverse drug reactions (acute laminitis and increased susceptibility to infections) were evident and the gelding was euthanized due to animal welfare considerations.

Periovulatory administration of firocoxib did not alter ovulation rates and mitigated post-breeding inflammatory response in mares

Non-steroidal anti-inflammatory drugs (NSAIDs) are a therapeutic option for the treatment of inflammation. However, negative effects of non-selective NSAIDs for treatment of mares with endometritis have been described, including delayed uterine clearance and impairment of ovulations. Firocoxib is a specific cyclooxygenase-2 (COX-2) inhibitor and has the ability to act in the uterus of mares. We investigated the effects of firocoxib on ovulation rate, numbers of polymorphonuclear neutrophils (PMNs), and COX-2 protein levels in the endometrial tissue of susceptible mares after insemination. Two experiments were conducted. In experiment 1, twenty mares were evaluated in two consecutive estrous cycles broken into the following groups: Control - no pharmacological interference; Treatment - mares were treated with 0.2 mg/kg of firocoxib orally. The treatment began on the day of ovulation induction, and firocoxib was administered until one day after artificial insemination (AI). Ovulation was induced with 1 mg of deslorelin acetate and the mares were inseminated 24 h after the injection. Ovulation was confirmed 48 h after induction, and embryos were collected eight days after ovulation. Experiment 2: Nine mares susceptible to persistent mating-induced endometritis (PMIE) were artificially inseminated. The mares were examined with ultrasound and inseminated with fresh semen in two consecutive cycles, control and treated, in a cross-over study design. The amount of intrauterine fluid was measured, and endometrial samples were collected 24 h after AI. The number of PMNs was determined by endometrial cytology and biopsy, and COX-2 labeling in endometrial samples was evaluated by immunohistochemistry. Firocoxib treatment did not induce ovulatory failure or affect embryo recovery rate in Experiment 1. In Experiment 2, firocoxib treatment reduced inflammation after AI in mares as evidenced with results regarding PMN numbers/percentage and endometrial COX-2 staining. In conclusion, the proposed treatment with firocoxib reduced endometrial inflammation in mares susceptible to PMIE after breeding, with no adverse effects.

Disposition and effect of intra-articularly administered dexamethasone on lipopolysaccharide induced equine synovitis

Background

Dexamethasone is used for the intra-articular route of administration in management of aseptic arthritis in horses. Despite its widespread use there is very little quantitative data of the disposition and response to dexamethasone. The aim of this study was to investigate and describe the synovial fluid and plasma dexamethasone concentration over time and to explore the relation between synovial fluid concentration and response using clinical endpoints as response biomarkers after IA injection of dexamethasone disodium salt solution in an equine model of synovitis.

Results

Inflammation was induced in the radiocarpal joint of six horses by injection of 2 ng lipopolysaccharide (LPS). Two hours later either saline or dexamethasone was injected in the same joint in a two treatment cross over design. Each horse was treated once with one of the six doses dexamethasone used (0.01, 0.03, 0.1, 0.3, 1 or 3 mg) and once with saline. Dexamethasone was quantified by means of UHPLC–MS/MS. Dexamethasone disposition was characterised by means of a non-linear mixed effects model. Lameness was evaluated both objectively with an inertial sensor based system and subjectively scored using a numerical scale (0–5). Joint circumference, skin temperature over the joint and rectal temperature were also recorded. The LPS-challenge induced lameness in all horses with high inter-individual variability. Dexamethasone significantly decreased lameness compared with saline. Other variables were not statistically significant different between treatments. Objective lameness scoring was the most sensitive method used in this study to evaluate the lameness response. A pharmacokinetic/pharmacodynamic model was successfully fitted to experimental dexamethasone and lameness data. The model allowed characterization of the dexamethasone synovial fluid concentration–time course, the systemic exposure to dexamethasone after intra-articular administration and the concentration–response relation in an experimental model of synovitis.

Conclusions

The quantitative data improve the understanding of the pharmacology of dexamethasone and might serve as input for future experiments and possibly contribute to maintain integrity of equine sports.

Modelling of oscillatory cortisol response in horses using a Bayesian population approach for evaluation of dexamethasone suppression test protocols

Cortisol is a steroid hormone relevant to immune function in horses and other species and shows a circadian rhythm. The glucocorticoid dexamethasone suppresses cortisol in horses. Pituitary pars intermedia dysfunction (PPID) is a disease in which the cortisol suppression mechanism through dexamethasone is challenged. Overnight dexamethasone suppression test (DST) protocols are used to test the functioning of this mechanism and to establish a diagnosis for PPID. However, existing DST protocols have been recognized to perform poorly in previous experimental studies, often indicating presence of PPID in healthy horses. This study uses a pharmacokinetic/pharmacodynamic (PK/PD) modelling approach to analyse the oscillatory cortisol response and its interaction with dexamethasone. Two existing DST protocols were then scrutinized using model simulations with particular focus on their ability to avoid false positive outcomes. Using a Bayesian population approach allowed for quantification of uncertainty and enabled predictions for a broader population of horses than the underlying sample. Dose selection and sampling time point were both determined to have large influence on the number of false positives. Advice on pitfalls in test protocols and directions for possible improvement of DST protocols were given. The presented methodology is also easily extended to other clinical test protocols.

Corticosteroids and Immune Suppressive Therapies in Horses

Immune suppressive therapies target exaggerated and deleterious responses of the immune system. Triggered by exogenous or endogenous factors, these improper responses can lead to immune or inflammatory manifestations, such as urticaria, equine asthma, or autoimmune and immune-mediated diseases. Glucocorticoids are the most commonly used immune suppressive drugs and the only ones supported by robust evidence of clinical efficacy in equine medicine. In some conditions, combining glucocorticoids with other pharmacologic and nonpharmacologic treatments, such as azathioprine, antihistamine, bronchodilators, environmental management, or desensitization, can help to decrease dosages and associated side effects.

Disease and pharmacologic risk factors for first and subsequent episodes of equine laminitis: A cohort study of free-text electronic medical records

Electronic medical records from first opinion equine veterinary practice may represent a unique resource for epidemiologic research. The appropriateness of this resource for risk factor analyses was explored as part of an investigation into clinical and pharmacologic risk factors for laminitis. Amalgamated medical records from seven UK practices were subjected to text mining to identify laminitis episodes, systemic or intra-synovial corticosteroid prescription, diseases known to affect laminitis risk and clinical signs or syndromes likely to lead to corticosteroid use. Cox proportional hazard models and Prentice, Williams, Peterson models for repeated events were used to estimate associations with time to first, or subsequent laminitis episodes, respectively. Over seventy percent of horses that were diagnosed with laminitis suffered at least one recurrence. Risk factors for first and subsequent laminitis episodes were found to vary. Corticosteroid use (prednisolone only) was only significantly associated with subsequent, and not initial laminitis episodes. Electronic medical record use for such analyses is plausible and offers important advantages over more traditional data sources. It does, however, pose challenges and limitations that must be taken into account, and requires a conceptual change to disease diagnosis which should be considered carefully.

Effect of Age, Season, Body Condition, and Endocrine Status on Serum Free Cortisol Fraction and Insulin Concentration in Horses

BACKGROUND

Increased free cortisol fraction is associated with insulin dysregulation (ID) in people with Metabolic Syndrome and Cushing's Disease. Free cortisol has not been investigated in equine endocrine disorders.

HYPOTHESES

(1) In healthy horses, sex, age, body condition score (BCS), and season impact free cortisol; (2) free cortisol is increased in horses with Pituitary Pars Intermedia Dysfunction (PPID) or Equine Metabolic Syndrome (EMS).

ANIMALS

Fifty-seven healthy horses; 40 horses and ponies with PPID (n = 20) or EMS (n = 20).

METHODS

Prospective study. Serum collected seasonally from healthy animals and archived serum from PPID and EMS animals was analyzed for insulin, total and free cortisol concentrations, and free cortisol fraction (FCF). Linear mixed models were used to determine effects of age, sex, season, and BCS on hormones in controls. Hormone measurements were compared between disease groups and age- and season-matched controls with t-tests. EMS and hyperinsulinemic PPID animals were combined in an ID (hyperinsulinemia) group.

RESULTS

Free cortisol concentrations were increased in overweight/obese controls (0.3 ± 0.1 μg/dL) compared to lean controls (0.2 ± 0.1 μg/dL; P = .017). Mean FCF was significantly higher in animals with PPID (8.8 ± 5.8 μg/dL, P = .005) or ID (8.8 ± 10.2 μg/dL, P = .039) than controls (5.0 ± 0.9 μg/dL), but total cortisol concentrations were similar (P ≥ .350) (PPID: 4.2 ± 4.3 μg/dL; ID: 5.0 ± 4.5 μg/dL; controls: 4.6 ± 1.7 and 5.1 ± 2.1 μg/dL).

CONCLUSIONS AND CLINICAL IMPORTANCE

Increased FCF is associated with obesity in healthy horses and with ID (hyperinsulinemia) in horses and ponies with endocrine disease. Decreased plasma cortisol-binding capacity could be a component of these endocrine disorders in horses.

Endoscopic Balloon Dilation of Esophageal Strictures in 9 Horses

Background

Medical treatment of esophageal strictures in horses is limited and the use of balloon dilatation is described in few cases. Long‐term follow up after balloon dilatation and the use of intralesional corticosteroids has not been evaluated.

Objectives

To describe the use of endoscopic guided, esophageal balloon dilatation in horses for cervical and thoracic esophageal strictures and administration of intralesional corticosteroids at the time of dilatation.

Animals

Nine horses from the hospital population with benign esophageal strictures.

Methods

Retrospective study: Medical records were reviewed from horses presented to the William R. Pritchard, Veterinary Medical Teaching Hospital at UC Davis from 2002 to 2013. Records were searched using the key words: equine, horse, balloon dilatation, bougienage, and esophageal stricture.

Results

Nine horses with esophageal strictures were treated with esophageal balloon dilatation. Five horses survived (survival at writing ranged from 2 to 11 years after discharge) and all nonsurvivors were <1 year of age and presented with concurrent problems or developed complications including megaesophagus, unresolved esophageal obstruction requiring esophagostomy, or severe aspiration pneumonia. Four horses were treated with intralesional corticosteroids with no adverse effects noted in the survivors (n = 3). Four horses available for long‐term follow up were alive at 2, 5, 6, and 11 years after presentation and 3 of these horses were being fed a hay‐based diet.

Conclusions

Resolution of esophageal strictures in the horse can be performed successfully, safely, and under standing sedation using balloon dilatation. Intralesional corticosteroids might reduce the incidence of recurrent strictures.

Treatment of idiopathic headshaking in horses with pulsed high-dose dexamethasone

BACKGROUND

Treatment of idiopathic headshaking in horses is complicated by an incomplete understanding of underlying pathophysiology and partially effective treatments. If an inflammatory etiology exists, corticosteroids could be beneficial.

HYPOTHESIS

An anti-inflammatory dose of dexamethasone reduces the signs of idiopathic headshaking in a field setting.

ANIMALS

Convenience sample of 20 adult horses with idiopathic headshaking syndrome. Cases were recruited from the general population and diagnosed by attending veterinarians.

METHODS

Prospective, blinded clinical trial. Pulsed dosing was with oral dexamethasone (60 mg PO Q24h × 4 days, q3 weeks for 4 months) or placebo (inert paste). Owners were blinded and asked to score the headshaking from 0 to 4 (4 = most severe) 3 days per week. The change in headshaking scores (HS) over each treatment pulse was compared between groups by ordinal logistic regression.

RESULTS

Twelve horses completed the trial. There was no significant difference between treated or placebo horses (P = .987). Sun (P ≤ .001), wind (P = .028), and exercise (P ≤ .045) significantly increased HS.

CONCLUSIONS AND CLINICAL IMPORTANCE

No benefit of dexamethasone treatment was detected for idiopathic headshaking. The results confirmed previous reports of common triggers for headshaking behavior

Omega-3 fatty acid supplementation provides an additional benefit to a low-dust diet in the management of horses with chronic lower airway inflammatory disease

Background

Omega‐3 polyunsaturated fatty acid (PUFA) may benefit humans and animals with chronic inflammatory diseases.

Hypothesis

Omega‐3 PUFA supplementation improves clinical signs, lung function, and airway inflammation in horses with recurrent airway obstruction (RAO) and inflammatory airway disease (IAD).

Animals

Eight research horses and 35 client‐owned horses.

Methods

A pilot study examined the dose of PUFA that can alter plasma PUFA composition. Then, a randomized, controlled clinical trial was performed in horses with RAO and IAD. Horses were fed a complete pelleted diet with no hay and randomly assigned to 1 of 3 daily treatments for 2 months: 30 or 60 g of the supplement or 30 g of placebo. Clinical signs, lung function, plasma PUFA composition, and bronchoalveolar lavage fluid (BALF) cytology were evaluated. Data were expressed as median (25–75th percentiles). P < .05 was considered significant.

Results

Polyunsaturated fatty acid supplementation resulted in increased plasma docosahexaenoic acid (DHA) that peaked at 4 weeks. Clinical improvement was noted in all horses involved in the clinical trial, but the group that received PUFA had greater improvement in clinical signs (cough score improved 60%), lung function (respiratory effort decreased 48%), and BALF (neutrophils decreased from 23 to 9%) when compared to placebo (cough score improved 33%, respiratory effort decreased 27%, BALF neutrophils increased from 11 to 17%; P < .05).

Conclusions and Clinical Importance

Feeding horses with RAO and IAD a PUFA supplement containing 1.5–3 g DHA for 2 months provides an additional benefit to low‐dust diet.

A review of recent advances and current hypotheses on the pathogenesis of acute laminitis

With the increasing number of studies being published on the different experimental models used to induce and study acute laminitis, the pathophysiological events associated with these various models (i.e. starch overload, oligofructose overload, black walnut extract and hyperinsulinaemia) can be compared more realistically. Within this review, the mechanisms for metabolic vs. inflammatory laminitis are discussed, and the question of how pasture laminitis may fit into any of the proposed mechanisms is addressed.

Clostridial myonecrosis, haemolytic anaemia, hepatopathy, osteitis and transient hypertrophic cardiomyopathy after intramuscular injection in a Thoroughbred gelding

A 9-year-old Thoroughbred gelding was presented for swelling over the left neck and inappetence. There was recent history of intramuscular administration of flunixin meglumine into the left neck. On examination, there was evidence of focal myositis, anaemia, haemolysis and pigmenturia. Culture of aspirated fluid from the left side of the neck produced a heavy growth of a Clostridium species. Complications of infection included haemolytic anaemia, hepatopathy, osteitis and transient hypertrophic cardiomyopathy. Treatment included intravenous fluid therapy, antibiotics, anti-inflammatory drugs, blood transfusion and surgical debridement. There was complete resolution of clinical, haematological, biochemical and echocardiographic abnormalities, and the horse returned to ridden work. This report highlights the complications that can arise from clostridial myonecrosis, including the effect on the myocardium.

Effect of ketoprofen treatment on the uterine inflammatory response after AI of jennies with frozen semen

Artificial insemination (AI) involving the placing of frozen-thawed semen directly into the jenny uterine body is associated with very low pregnancy rates. This might be because of an exacerbation of the acute response of the endometrium to sperm, as seen in mares with persistent induced mating endometritis. Pregnancy rates can be increased in such mares, however, by including anti-inflammatory treatments in the insemination protocol (Bucca S, Carli A, Buckley T, Dolci G, Fogarty U. The use of dexamethasone administered to mares at breeding time in the modulation of persistent mating induced endometritis. Theriogenology 2008;70:1093-100; Rojer H, Aurich C. Treatment of persistent mating-induced endometritis in mares with the non-steroid anti-inflammatory drug vedaprofen. Reprod Domest Anim 2010;45:e458-60). To investigate the endometritis caused by the use of frozen-thawed semen in jennies, and to assess the response to ketoprofen treatment, endometrial cytological samples and biopsies from six healthy jennies were examined in a crossover design experiment. Samples were taken from jennies in estrus (E; control) and at 6 hours after AI with or without ketoprofen (+K and -K, respectively). Ketoprofen was administered iv 24 hours before and for 4 days after insemination (total = 2.2 mg/kg/24 hours for 5 days). All animals showed a severe inflammatory response to semen deposition. Polymorphonuclear neutrophil numbers in the cytological smears and biopsies differed significantly between the +K and E animals. No significant differences were recorded, however, between the +K and -K treatments. Eosinophils were observed in all sample types from all groups; these cells appear to be a feature of the normal jenny endometrium. Slight fibrosis was observed in some biopsies, but no significant relationship with inflammation was found. Intense cyclooxygenase-2 (COX-2) immunohistochemical labeling was detected in the -K biopsies. Less intense labeling was seen in those of the +K animals, and mainly localized in the stratum compactum. No differences in COX-2 labeling were observed between the +K and E animals. Plasma concentrations of ketoprofen remained detectable until 2 hours after administration, after which the compound was rapidly eliminated. In summary, jennies are susceptible to endometritis after insemination with frozen-thawed semen. Ketoprofen reduces this inflammation by inhibiting COX-2; no reduction in the number of polymorphonuclear neutrophils occurs. The physiological and pharmacological characteristics of jennies should be taken into account when designing treatments for acute endometritis aimed at enhancing pregnancy rates after insemination with frozen-thawed sperm.

The effects of prolonged endurance exercise on the neurological system in horses

Horses compete routinely in endurance-type activities. Many of the various pathophysiological mechanisms which arise during endurance exercise have implications for the health and function of the neurological system. The development of centrally-mediated fatigue is a normal homeostatic physiological event with several possible mechanisms. Development of pathophysiological phenomena such as cerebral oedema may be near-terminal events during or after endurance exhaustion. Cellular damage resulting in cytotoxic cerebral oedema may result from decreases in circulating blood volume (dehydration), blood pressure, oxygen, and glucose, or increases in brain temperature. Vasogenic cerebral oedema arises from changes in cerebral vascular perfusion, tone, and permeability. Increased vascular permeability results from increased brain temperature, poor vascular integrity due to severe dehydration, disseminated intravascular coagulation due to hemoconcentration or endotoxemia, and iatrogenic overhydration during therapy. Clinical signs of intracranial disease after endurance exercise include staggering, shaking, ataxia, paresis, poor tongue tone, facial twitching, collapse, recumbency, seizures, and death. Treatment should include active and aggressive cooling, intravenous polyionic fluids, acid-base imbalance correction, intravenous glucose and calcium supplementation, non-steroidal anti-inflammatory agents once the patient is better hydrated, intra-nasal oxygen therapy if practicable, and achievement of a non-dependent head posture to prevent jugular venous hypertension and further increases in intracranial pressure. The prognosis for central fatigue is good with appropriate supportive care, but the prognosis for successful treatment of cerebral oedema must be considered guarded at best. Prevention is critical and must be through incorporation of mandatory rest stops with sufficient length and veterinary monitoring to allow prevention and detection of exhaustion, excessive dehydration, and neurological signs. Management flexibility in shortening or postponing rides in hot and humid conditions, mandated use of aggressive cooling techniques, and more restrictive entry criteria for upper level Fédération Equestre Internationale races should all be considered as viable options for optimising the safety of endurance horses.