diagnostic approaches for the assessment of equine chronic ... · original research diagnostic...

Journal of Equine Veterinary Science xxx (2011) 1-11

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Journal of Equine Veterinary Science

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Original Research

Diagnostic Approaches for the Assessment of Equine ChronicPulmonary Disorders

Orsolya Kutasi DVMa, Nandor Balogh PhD, dipl. ECVCP b, Zoltan Lajos DVMc,Krisztina Nagy PhD a, Otto Szenci DVM, PhD, DSc, Dip. ECBHMa

a Clinic for Large Animals, Szent Istvan University, Üll}o, Dora Major, Hungaryb PraxisLab Kft, Budapest, HungarycDuo-Bakt Veterinary Microbiology Laboratory, Budapest, Hungary

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Keywords:Chronic pulmonary disordersConditional inference treeDiagnostics

Corresponding author at: Orsolya Kutasi, DVMAnimals, Faculty of Veterinary Science, Szent Istvan UnDora Major, Hungary.

E-mail address: [email protected] (O. Ku

0737-0806/$ - see front matter � 2011 Elsevier Inc. Adoi:10.1016/j.jevs.2011.03.018

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a b s t r a c t

Even though the respiratory system is one of the most accessible organs for diagnostictesting, it is not always easy to define chronic lower airway disease in the horse. Diag-nostic procedures performed by first opinion veterinarians in the field are oftenrestricted to taking the history and performing clinical examination. Respiratory tractendoscopy, tracheal or bronchoalveolar lavage, and blood sampling are sometimes usedbut other specific ancillary examinations are seldom performed in stable settings.Therefore, our objectives were to evaluate the diagnostic value of different techniquesand examination types routinely used in the diagnostic workup of chronic equine lowerairway cases in both stable and clinical circumstances. Another aim of this study was toestimate the prevalence of different chronic pulmonary disorders among horsesadmitted to a Hungarian referral clinic. According to the conditional inference treemethod, age of the horse, history, clinical examination, respiratory tract endoscopy, andbronchoalveolar lavage cytology proved to be the most valuable tools to definepathology. It was also concluded that in 22% of cases, more specific ancillary diagnosticmodalities, unavailable for the field veterinarian, were needed to establish the finaldiagnosis. According to our study, the most frequently diagnosed chronic pulmonarydisorders in Hungary are of noninfectious origin, principally recurrent airway obstruc-tion. Regardless of the cause, and interestingly including recurrent airway obstruction aswell, these diseases occur primarily during the warm months.

� 2011 Elsevier Inc. All rights reserved.
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1. Introduction

After establishing a definite diagnosis in as manypulmonary cases as possible, a significant number of horsesare always left with no definitive diagnosis evenwhenusingcurrent understanding and available ancillary diagnostictechniques [1]. Although an accurate history and especiallybronchoscopy can confirm the presence of pulmonarydisease, pulmonary cytology forms a mainstay for

, Clinic for Largeiversity, 2225, Üll}o,

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diagnosing the specific chronic pulmonarydisease using thecriteria described in previously published data [2].

Chronic lower airway disorders can be of several originssuch as allergy, hypersensitivity, infections, toxicity, loss ofpulmonary vascular integrity, or neoplasia. One of the mostcommonly diagnosed chronic lower airway diseases isrecurrent airway obstruction (RAO) [2], which is believed tobe caused by an allergic reaction to inhaled molds andshares similarities with the noneosinophilic form of asthmain human beings [3-5]. Airway obstruction, inflammation,mucus accumulation, and tissue remodeling have beenshown to contribute to the pathophysiology of RAO [6].Airway obstruction causing typical labored breathing isreversible by controlling dust in the environment or using

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http://dx.doi.org/10.1016/j.jevs.2011.03.018

http://dx.doi.org/10.1016/j.jevs.2011.03.018

O. Kutasi et al. / Journal of Equine Veterinary Science xxx (2011) 1-112

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bronchodilators [6]. A mild form of lower airway inflam-matory disease commonly encountered in young athletichorses has been recognized as a separate entity from RAOand is termed inflammatory airway disease (IAD) [7-9]. Inthe majority of cases, RAO and IADmay be differentiated onthe basis of clinical grounds; however, some have arguedthat, over time, horses with IAD may progress into RAO[10,11]. In the pathogenesis of IAD, a variety of causal agentsmight be involved, such as respirable organic and inorganicparticles in stable dust [12], immunological factors, andinfectious agents [9,13]. Although IAD is a nonsepticinflammation of the lower airways without any evidence ofsystemic signs of infection, in a previous study, a clearassociation was demonstrated between some infectiousagents and the prevalence of IAD [13]. Infections causinglower airway disease in adult horses include viral, bacterial,fungal, and parasitic agents, and they more typically occurafter a predisposing effect that suppresses pulmonaryimmunity like long-distance transport or strenuous exer-cise, resulting in systemic signs [14]. Exercise-inducedpulmonary hemorrhage (EIPH) occurs in the majority ofracehorses and is observed sporadically in many othersport horses that require strenuous exercise for shortperiods [14,15]. Proposed pathophysiological mechanismsinclude high pulmonary vascular pressures duringmaximal exercise as well as pulmonary inflammation orobstruction of the upper or lower airways [14,16,17]. Otherlower airway disorders like granulomatous, neoplasticdiseases, or interstitial pneumonias are rarely diagnosed inhorses [14]. Differentiation between the aforementionedlower airway respiratory disorders on the basis of theirflexible and ambiguous definitions can sometimes bedifficult or even impossible. Clinical signs and the causalfactors may overlap, or one of these disorders may inducethe other. Because treatment and prognosis can signifi-cantly differ, an appropriate diagnosis is always necessary.

Our objectives were to evaluate the diagnostic value ofdifferent techniques and examination types used routinelyin the diagnostic workup of chronic equine lower airwaycases by field veterinarians and in clinical circumstances.Another aim of this study was to estimate the prevalence ofdifferent equine lower airway diseases among horsesadmitted to a Hungarian referral clinic.

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2. Materials and Methods

The study was performed between July 2005 andAugust 2008, at the Clinic for Large Animals, Faculty ofVeterinary Science, Szent István University. In total, 100horses (25 stallions, 39 geldings, and 36 mares) of different

Table 1Simplified history questionnaire focusing on differentiation between environme

Score Duration ofDisease

Course of Disease Stabling

0 >4 weeks Continuous signs Pasture

1 >6 weeks Hypoallergenic band soaked ha

2 >8 weeks Remission-exacerbation Simple stabling

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breedsd61 Hungarian Half-breeds, 10 other EuropeanHalf-breeds, nine Lipizzaner, five Friesians, four Thor-oughbreds, four ponies, four Arabians, and three AmericanBreedsdaged 1 to 17 years (mean: 9.1 � 2.8 years), withchronic respiratory symptoms such as cough, nasaldischarge, dyspnea, or poor performance were included inthis study. Chronicity of a minimum of 4 weeks was theminimum requirement for inclusion in the study. Most ofthe equine patients (76%) were referred for a secondopinion. The same standardized examination protocol wasfollowed in all cases.

2.1. Examination Protocol

2.1.1. HistoryA special questionnaire was developed for taking the

history. Breed, age, gender, usage of the horse, anda complete history with presenting signs, disease process,duration and type of previous treatments, and stablingconditions were recorded. Then, on the basis of these data,a simple scoring system was established to evaluate thestabling technology and disease process for statisticalanalysis (Table 1). The months of clinical admission forexamination and disease establishment or exacerbationswere noted. Referring surgeons were questioned aboutdiagnostic techniques they used in each particular respi-ratory case and also about their suspected diagnosis.

2.1.2. Clinical ExaminationA general physical examinationwas performed about 60

minutes after the horse arrived at the clinic. The mainfindings regarding the respiratory tract (RT) were evaluatedwith clinical scores on the basis of the methods developedby Naylor et al. [18] and Traub-Dargatz et al. with slightmodifications [19] (Table 2). The sum of the numbersassigned to the different symptoms was used to generatethe general clinical severity score.

2.1.3. RT EndoscopyIn the majority of the cases, RT endoscopy (CF-VL,

Olympus GmbH, Hamburg, Germany) was performedwithout sedation to obtain most of the information aboutthe function of both the lower and upper airways. Innoncooperative animals, sedation with detomidine (10 mg/bwt; Domosedan inj.; Orion Pharma, Espoo, Finland) incombination with butorphanol (10 mg/bwt; Alvegesic inj.;Alvetra u. Werfft GmbH, Wien, Austria) was used. The nasalpassages, pharynx, larynx, and guttural pouches wereinspected and the upper respiratory tract (URT) was eval-uated with score 0 if negative and with score 1 if any

ntal-induced and infectious disorders

Infection Treatment SteroidAnti-Inflammatory Drug

Fever, companion animalswere affected

No or negative reaction

eddingy

No treatment

No fever, no other horseaffected

Positive reaction

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Table 2Clinical severity scoring system (according to Naylor et al. [18] and Traub-Dargatz et al. with modifications [19])

Score RespiratoryRate

Respiratory Effort Lung Auscultation Cough Nasal Discharge

0 <20 No Normal No No or serous1 20e30 Increased Increased bronchial sounds Induced, strong Mucinous2 30< Expressed intercostals muscle contraction

and abdominal liftLocal wheezes and crackles Spontaneous, frequent

or boutsMucopurulent

3 Flared nostrils and anal movement Generalized wheezes and cracklesor reduced lung sounds despitedeep breath

O. Kutasi et al. / Journal of Equine Veterinary Science xxx (2011) 1-11 3

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functional disorder was suspected. The volume of therespiratory secretion (RS) present in the cranial thoracictrachea was semiquantitatively described according to thegrading system by Gerber et al. [20]. The nature of the RSwas also recorded as mucoid, mucopurulent, purulent, orhemorrhagic. Tracheal and bronchial respiratory mucosawas also examined for evidence of inflammation, that is, forbluntness of the normally sharp carina and for the presenceof hyperemia. End expiratory bronchoconstriction orbronchial collapse was also noted.

2.1.4. Respiratory (Tracheal) Secretion Cytology and CultureRS was collected transendoscopically through the work

channel using a sterile 2-m long plastic catheter (PW1V,Olympus GmbH, Hamburg, Germany). Within 1 hour ofcollection, an air-dried smear of RS was prepared and fixedwith a fixative, and a differential cell count of 100 cellswas performed on a Diff-Quick (Reagens Kft., Budapest,Hungary) stain preparation. The sample was sent forbacteriology when secretion was macroscopically consid-ered purulent or the history had described a previous sus-pected RT infection or the results of clinical examinationswere suspicious of infectious origin. Samples were injectedto a transport media and sent for culturing to a specializedveterinary microbiology laboratory.

2.1.5. Bronchoalveolar Lavage Fluid Cytology and CultureIn each case, bronchoalveolar lavage fluid (BALF) was

obtained through a BIVONA catheter (Bivona MedicalTechnologies Inc., Gary, IN) with horses under sedation aspreviously described. To reduce the physical irritation ofthe mucous membrane, 0.5% lidocaine solution (Lidokaininj.; Richter Gedeon Nyrt., Budapest, Hungary) was sprayedon the carina, and then 350 mL of lukewarm saline was

Table 3Supplementary diagnostic procedures in selected cases (performed as described

Type of Examination Number ofTested Animals

Indication

Thoracic radiography 51 Moderate oArterial blood gas analysis 43 Moderate oThoracic ultrasonography 35 Distorted lHematology 20 History ofSerology 12 History ofCulture on BALF 12 History of

lung patBronchodilator (atropine)

administration10 Severe dys

Treadmill endoscopy 6 Supposed dMolecular diagnostic tests 3 Fever, nonLung biopsy 1 Nonrespon

BALF, bronchoalveolar lavage fluid; URT, upper respiratory tract.


instilled and aspirated. The volume of fluid gained back, itstransparency, color, and the presence of a foamy layer wererecorded. Within 30 minutes of collection, BALF cytospincell preparations were made. Romanowsky stain (Diff-Quik; Reagens Kft., Budapest, Hungary) was used, whilekeeping in mind that this stain has been found to beinadequate for detecting pulmonary mast cells [21,22].Differential cell counts were performed on 300 cells bya board-certified clinical pathologist blinded to the clinicaland endoscopic findings. Values given by Derksen et al. [23]were used as references.

In 67 cases of the supplementary laboratory examina-tions (48/67), further diagnostic imaging procedures (67/67) or bronchodilator test (10/67) with 0.02 mg/kg intra-venous atropine (Atropinum sulfuricum inj., Egis, Budapest,Hungary) were performed (Table 3).

2.2. Diagnostic Criteria Used to Classify Cases

2.2.1. RAO/HeavesRAO was defined as chronic neutrophilic pulmonary

inflammation associated with the presence of hay and/orstraw in the affected horses’ environment and with clinicalmanifestations varying from mild cough to severe dyspneaat rest. The BALF of horses with RAO showed moderate tosevere neutrophilia (>20% cells), decreased lymphocyte,and alveolar macrophage counts [25,26]. Summer pasture-associated (SPA)-RAO is clinically indistinguishable fromRAO except that the affected horses develop signs whilemaintained on pasture [9].

2.2.2. IADBy definition, horses with IAD might show poor

performance, exercise intolerance, or coughing, with or

by Lekeux et al. [24])

r severe clinical signsr severe resting dyspnea or tachypnoeaung borders on percussion or positive thoracic radiographyfever, depression, or weight lossfever or more horses affected simultaneously nearbyfever, or suspected respiratory infections, or diffuse abnormalterns on thoracic radiographiespnea

ynamic URT disorders based on history or resting endoscopy findingsresponsive to antibiotic treatments and interstitial radiographic patternsive to any treatment, nodular interstitial radiographic pattern

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without excess tracheal mucus, but without showingdepression, fever, or increased respiratory efforts at rest [9].It is commonly reported in young racehorses and decreasesin frequency with increasing age [13], but nonracehorses ofall ages can have IAD [9,26]. The most commonly encoun-tered BALF cytologic profiles are characterized by increasedtotal nucleated cell count with mild neutrophilia, lympho-cytosis, monocytosis [7,9,26], or eosinophilia [27,28].Although neutrophilic inflammation is commonly observedinBALF fromhorsesbothwithRAOand IAD, theneutrophiliais usually less pronounced in cases of IAD (ie, <20%).

2.2.3. Infectious DisordersManifestations of infection such as lymphadenitis, fever,

depression, decreased appetite, and weight loss are usuallypresent in lower airway diseases of bacterial, viral, fungal,or parasitic origin [9]. Diagnosis is based on a positiveculture with concurrent suggestive cytological findings(intracellular bacteria or fungal spores and signs ofneutrophilic degeneration, like swollen nuclei or kar-yolysis) of tracheal wash fluid or an increase in antibodytiter over the course of the disease within 14 to 21 days insuspected viral infection or a positive result of othermolecular diagnostic tests.

2.2.4. Upper Respiratory Tract Functional Disorders withSmall Airway Inflammation

Upper airway endoscopy at rest or during exerciseallows for the identification of significant upper airwaydiseases. Concurrent abnormal bronchoalveolar lavage(BAL) cytology reflects lower airway inflammation. Horseswith mild upper respiratory tract functional disorders(URTFD), expiratory dyspnea at rest, and BAL cytology ofneutrophils of >20% were classified as RAO cases andURTFD was evaluated as coincidence findings.

2.2.5. Exercise-induced Pulmonary HemorrhageEIPH occurs primarily in horses performing short

periods of high intensity work. The diagnosis is based onfinding blood after performing bronchoscopy [29] or bydetecting increased hemosiderin content within alveolarmacrophages [30,31].

2.2.6. Chronic Interstitial Lung Diseases of NoninfectiousOrigin and Neoplasia

The interstitial lung disease is generally unresponsive toantimicrobial and anti-inflammatory therapy. Thoracicradiographs commonly show severe, diffuse, or nodularinterstitial pattern. A transthoracic lung biopsy is thedefinitive test for diagnosing chronic interstitial lungdisease or neoplasia [32].

2.2.7. Undifferentiated Pulmonary DisordersThis group was composed of animals with detectable

pulmonary disease where the diagnosis did not fall clearlyinto any of the aforementioned categories.

2.3. Statistical Analysis

To compare the history (Table 1) of horses with orwithout RAO, Fisher’s test was used. To evaluate theusefulness or necessity of the different examination types


used in the diagnostic workup of chronic equine lowerairway and pulmonary cases, data were analyzed by usingconditional inference tree methods [33]. First, we summedthe historical and the clinical scores separately (scoresare presented in Tables 1 and 2) and used these two newvariables in a conditional inference tree model, whichbasically represents the decision-making paradigm fre-quently used in field veterinarian practice. Second, weadded all the measured variables (age, gender, breed of thehorse, historical data listed in Table 1, month of admission,clinical parameters listed in Table 2, RT endoscopy, RScytology and bacteriology, BALF cytology, arterial blood gasand pH measurements, and x-ray and ultrasound findings)into another conditional inference tree model to see howmuch the decision-making rule might improve by usingthese ancillary tests.

Conditional inference trees were constructed withcquad-type test statistics and a ¼ 0.10 with simple Bonfer-roni correction. Each split needed to send a minimum of 3%of the observations into each of the two child nodes. Allanalyses were performed using the R 2.7.2. StatisticalSoftware Q[34].

3. Results

Overall, out of the 100 horses used in this study, 76 caseswere referred by 45 veterinarians for a second opinion.They performed physical examination in all cases. RTendoscopy was carried out only in 22 cases with takingtracheal sample for culture and for cytology in 20 and eightcases, respectively. Blood was taken for hematology on 20occasions, and BALF was sent for cytology on six occasions.Suspected diagnoses by field veterinarians were heaves(49/76) or respiratory infection (12/76), whereas the rest ofpatients were referred without any previous diagnosis.

On the basis of the BAL cytology, all of the examined 100horses had some type and degree of lower airway disorder.

The case selection comprised horses with RAO (n ¼ 54),IAD (n ¼ 20), infectious pulmonary disease (n ¼ 9), URTFDwith SAI (n ¼ 13; which consisted of idiopathic left laryn-geal hemiplegia [n ¼ 4], dorsal displacement of the softpalate [n¼ 4], pharyngeal collapse [n¼ 1], tracheal collapse[n ¼ 1], subglottic Qcyst [n ¼ 1], fourth branchial arch defect[n ¼ 1], and arytenoid chondritis [n ¼ 1]), and undiffer-entiated cases (n ¼ 4). We did not group any animal asprimary EIPH case, but we had horses with erythrophagesin their BAL in all other groups except the undifferentiatedone. During the examined period we did not diagnose anyneoplasia or interstitial lung disease of noninfectiousorigin.

Chronic pulmonary disorders were more likely to bediagnosed during the warm months (87% of the cases werediagnosed between March and November), and mosthorses started to show symptoms or had exacerbatedclinical signs also during this period. The distribution ofthe onset dates shows a trend for three main peaks duringthe year for patients with RAO and IAD: one peak at thebeginning of spring, a second smaller peak in the middle ofsummer, and another peak at the end of summer (Fig. 1).Clinical admission dates clearly follow the peaks of onset.

The mean (SD) time span between the onset of thedisease and the clinical admission was 4.4 � 3.7 months,

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web4C=FPO

Fig. 1. The time-distribution of disease onset, clinical admission, and air-borne pollutants (fungal spores, pollen).


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during which 66% of the animals were not treated at all ortreated with no success (19%).

Horses were used for pleasure riding (48%) or sports(52%), and the majority of them (71%) were kept in stableswith the traditional Hungarian stabling technology offeeding dry hay and bedding with straw. Some owners(24%) had already implemented changes in this technologyand introduced new hypoallergenic materials for beddingand used soaked hay. Only five horses, all of them diag-nosed with RAO, were kept on pastures, but these animalsalso had supplementary dry hay almost year round.

Horses with RAO were significantly older as comparedwith those with IAD (P < .001), URTFD (P ¼ .022), orinfectious disorders ([ID]; P < .001). The average (SD) ageswere 10.8 (2.7), 6.3 (1.4), 8.3 (3.8), and 6.0 (3.3) years,respectively. Horses with IAD, URTFD, or ID did not differsignificantly from each other regarding age. Horses withRAO were 3.4 times more likely to have a duration ofrespiratory symptoms for>8 weeks (Fisher’s test, P¼ .022),were 5.0 times more likely to show remission-exacerbation(Fisher’s test, P ¼ .002), and were 3.4 times more likely toshow no fever (Fisher’s test, P ¼ .023), as compared withhorses diagnosed with other chronic pulmonary disorders.

Regardless of the final diagnosis, the most commonpresenting clinical sign was cough (63%), and the leastcommon was poor performance (10%). Nasal discharge anddyspnea were recorded in 41% and 40% of the cases,respectively.

The result of the first tree model (Fig. 2), in which weused the data usually available through history question-naire and physical examination carried out by field practi-tioners in the classification of horses suffering frompulmonary disorders, suggests that horses with RAO willmost likely be found among horses with summed clinicalscores and summed historical scores >4. According to thistree model, 38 of the 54 RAO horses and five of nine IDhorses could possibly be classified correctly as RAO or IDpatient. However, 13 of the 46 non-RAO patients were alsoclassified with this tree model as horses suffering from


RAO. None of the 20 IAD and 13 URTFD cases was classifiedcorrectly by this model.

For the second tree model, we added the data of ancil-lary diagnostic procedures (RT endoscopy: URT scoring andtracheal mucus grading, tracheal secretion cytology andbacteriology, BALF cytology, arterial blood gas measure-ments, as well as thoracic X-ray, and ultrasound). Results ofURT endoscopy, neutrophil percentage in the BALF, historyof previous infection, and age variables were selected as themain diagnostic criteria by the model (Fig. 3).

The first splitting criteria of the tree model resulted ina group of horses in which the endoscopy was positive forURTFD. A total of 76.5% of these horses had URTFD and23.5% were diagnosed with RAO. All of the URTFD horses,except for 7% of the RAO horses, belonged to this group.

The second most important grouping variable was theneutrophil percentage in the BALF. In cases where endos-copy was negative and neutrophil granulocyte percentagewas <23%, none of the horses were diagnosed with RAO.

Among horses that had negative URT endoscopy anda neutrophil granulocyte percentage >23%, RAO was mostprevalent if horses had a history without fever and wereaged >6 years (93% of the horses suffering from RAO werefound in this group).

Within the group of horses with negative URT endo-scopy, a neutrophil granulocyte percentage >23% anda history of fever, 57% of horses were diagnosed with RAO,and 43% of them with ID (in total, 15% of horses diagnosedwith RAO and 67% with ID were found among this group ofhorses).

With the help of this tree model, 41 of the 54 RAOhorses, 14 of 20 IAD horses, and all 13 URTFD horses wereclassified correctly as RAO, IAD, or URT patient. Only threeof the 46 non-RAO patients were classified as horsessuffering from RAO. None of the nine ID cases was classifiedcorrectly by this model.

Because of the small sample size, we were not able topresent statistically significant correlations, but the resultsof further laboratory, diagnostic imaging, and other

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Fig. 2. Conditional inference tree built by using data usually available through physical examination and history. RAO, recurrent airway obstruction; IAD,inflammatory airway disease; URTFD, upper respiratory tract functional disorders with small airway inflammation; ID, infectious disorders, UPD, undifferentiatedpulmonary disorders.


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supplementary findings giving relevant information arepresented in Table 4. Finally, four cases remainedundifferentiated.

In contrast to this, 40% of RAO and 75% of ID patientswere eventually misclassified by the field practitionerspreviously.

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4. Discussion

According to the present study, the most frequentlyoccurring chronic pulmonary disorders in Hungary are ofnoninfectious origin, principally RAO, which is similar toprevious data on horses, presented for evaluation to NorthAmerican [14] and British [2] referral clinics. RAO and IADhave been reported worldwide, but their incidence ishighly variable and may depend on regional climaticfactors, in particular temperature and precipitation [3]. Theincidence of RAO is reported to be high in countries witha cool and wet climate and low in regions with a warm anddry climate [3,35,36]. Although Hungary has a relative dryand warm continental climate as compared with otherwestern and middle European countries, RAO seems to bea very common respiratory disorder.

Regardless of the initiating cause, the most clinicaladmissions with respiratory disorders took place duringthe warm months, between March and November, whenstables were open andmost horses had some limited accessto paddocks and pastures.


Seasonal occurrence can also be a typical feature ofsome diseases. As RAO is associated with exposure to hayand straw, as was previously described, it should be morecommon when horses are stabled during the winter[14,36,37]. Interestingly, in the present study, RAO hada higher prevalence during the spring and summertime ascompared with the winter season. Conversely, Couëtil et al.[38] described that horses were 1.6 and 1.5 times as likelyto be examined for RAO during the winter and spring,respectively, than they were during summer. In this study,the rapidly increasing number of cases in early springcoincides with the increase in pollen levels, the peak inJune follows the increase in the outdoor-measured air-borne mold content, and the third peak overlaps thehighest level of pollen particles [39]. Although most ofthese horses were maintained in stable environment, wecould not exclude that SPA-RAO induced by pollen allergyand other outdoor aeroallergens might coexist in suchcases. Ward and Couëtil [3] have also described that theprevalence of RAO correlated with outdoor aeroallergenlevels. According to the previously published data,however, classical RAO of stabled animals occurs during thewinter or early springtime when horses are kept in closedbarns and fed with dry hay [3,8,14,16,35]. As evidenced byour results, strictly following the previously published datawith respect to the seasonal prevalence of RAO may resultin a false diagnosis. Concurrent SPA-RAO complicates bothevaluation and management of these horses and isa significant problem in Hungarian climatic and geographic

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Fig. 3. Conditional inference tree built by using data when added the results of ancillary diagnostic procedures. RAO, recurrent airway obstruction; IAD,inflammatory airway disease; URTFD, upper respiratory tract functional disorders with small airway inflammation; ID, infectious disorders; UPD, undifferentiatedpulmonary disorders.Q7


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conditions. Five horses in the RAO group were kept onpasture during the entire year and experienced exacerba-tion during the warm months, but the original onset of thedisease occurred when these horses had previously beenmaintained in a stable environment. Although the fieldveterinarian directed these patients to pastures, however,environmental control was not successful in these casesbecause the climate of Hungary makes hay supplementa-tion necessary even during the summer months. Bothoutdoor aeroallergens and dry hay supplementation mightbe responsible for these exacerbations.

As described in other studies, weeks to months maypass between the onset of clinical signs in the field and thetime of clinical admission [2,38]. This might also influenceour results regarding seasonal prevalence. Generally,more than 4 months passed during which the horsesstarted representing clinical signs but were not examined,diagnosed, or treated at all. Subtle clinical signs usually donot alert owners and delay veterinary examination. Thistime delay might complicate diagnostic workup in severalcases but makes RAO differentiation easier with recordedexacerbation-remission periods and relatively longerdisease duration.

Details in the history about antecedent respiratoryinfectionwere not an exclusive feature of the cases in the IDgroup. We had horses in the IAD group that were referredas cases with suspected complications after some infection


in the previous 6 months. Dixon et al [2] described that19.2% of COPD Q-affected horses had an infection immedi-ately preceding the current respiratory disorder; in addi-tion, according to Couëtil et al [11], owners often reporta history of infectious respiratory disease in the monthspreceding the diagnosis of IAD with several horses in thestable being affected. The role of infectious agents in thedevelopment of RAO and IAD is still not clear [6,9].

Although age is a helpful parameter when identifyingcases of heaves, we also had horses in this group as youngas 6 years of age. By contrast, our IAD group consisted ofolder horses than generally described in the previouslypublished data [9,40].

First opinion veterinarians usually have limited possi-bilities to perform special laboratory or any diagnosticimaging techniques. On the basis of the present study,a specific questionnaire regarding history and a thoroughclinical examination can be reliable in diagnosing horseswith RAO. Hotchkiss et al. [41] have previously demon-strated the usefulness of a well-constructed questionnairein discriminating between horses with and without RAO.Another study also emphasized that the majority of caseswith heaves can be correctly diagnosed on the basis ofphysical examination [18]. According to our study, thesecases with typical history and unequivocal clinical signs ofheaves accounted for 70% of the RAO patients, whichaccounted for only 38% of all cases. This reflects other

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Table 4Additional findings of laboratory, diagnostic imaging, and other supplementary procedures

Type of Examination Findings Number of positive cases/final diagnosis

RAO IAD ID URTFDwith SAID

Undifferentiated

Bronchoscopy Bronchoconstriction 9 1 1Food particles in trachea 4Hemorrhagic mucus in trachea 2

Tracheal cytology Septic inflammation 2 10 2Tracheal culture StreptococcusQ8 zooepid (n ¼ 4), Streptococcus

Equi (n ¼ 2), Klebsiella pneumonia (n ¼ 1),Actinobacillus Equuli (n ¼ 1),Staphylococcus aureus (n ¼ 1)

2 6 1

BALF cytology additional findings Hemosiderophages 1 2 2 1Intracellular plant or pollen particles 4 2 5

BALF culture Str zooepidemicus (1) 1Thoracic radiology Severe bronchial pattern 14 1

Increased radiolucency with concave diaphragm 3Bronchiectasis 2Increased interstitialebronchial pattern 6 8 2 3Increased interstitial pattern 2 1

Thoracic ultrasonography Caudally displaced lung borders 5Cranially displaced lung borders 1 1Comet tail echoes 5 8 3 4Subpleural hypoechogenic areas 4

Bronchodilator administration Positive 7Negative 1 2

Serology EHV4Q9 (n ¼ 2), equine virusarteritis (n ¼ 1) 2 1Hematology anemia 1

lymphocytosis 1eosinophilia 1

PCR EHV5 1Lung biopsy Nodular fibrosis 1

RAO, recurrent airway obstruction; IAD, inflammatory airway disease; URTFD, upper respiratory tract functional disorders; SAID, small airway inflammatorydiseaseQ10 .


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previous data indicating that history taking and the resultsof physical examinations were not sufficient to establisha respiratory diagnosis [26,42]. None of the clinical signswere typical for any disorder. More severe respiratorysymptoms were suggestive for RAO or ID, but history couldhelp to differentiate between them.

Performing BAL and evaluating the cytology sample hada great effect on carrying out a successful diagnosticworkup. Increased neutrophil counts are the main diag-nostic criteria for RAO, but cutoff values vary greatly amongpublications depending on the BAL technique used or thepopulation studied [31]. Because we had no previous dataconcerning our technique and horse population, wedecided to possibly include equine patients in the RAOgroup with neutrophils of >20%. Finally, we realized thatour cases with heaves had >23% of neutrophils in theirBALF. This finding is rather in agreement with the proposalthat >25% neutrophils in BAL are necessary for a horse toqualify as being affected with RAO [8]. Neutrophilia in theBAL sample was prominent in the RAO horses as well as inmost of the ID-affected horses, which complicated differ-entiation on the basis of cytology. BAL cytology resultscombined with no previous febrile period history and theage of the horse resulted in the identification of most of thepatients with RAO.

Although lower airway disorders cannot be differenti-ated on the basis of RT endoscopy, endoscopy is the uniquemethod to define URTFD [43,44]. Simple respiratoryendoscopy at rest selected all URTFD cases. In our caseload,none of the animals presented with suspicion of upper


airway dysfunction. Cough, nasal discharge, and dyspneacan be caused by upper airway inflammation andobstruction as well [9,45]. Interestingly, all of the horseswith URTFD also had abnormal BAL cytology results indi-cating small airway involvement, which might also beresponsible for the clinical signs. Small airway inflamma-tion (SAI) in these cases could have possibly been caused bythe altered airflow dynamics causing decreased mucocili-ary clearance and more negative pressure in the lowerairway segments resulting in mechanical irritation orhemorrhage. Mild chronic aspiration and secondary infec-tions could contribute to the disease. In a previous studyabout URT functional problems, the authors also suggestedtheir predisposing role in lower airway inflammation [46].Depending on each individual case, we have found variouscytological findings with different increased cellular ratios.Increased neutrophil and exfoliated epithelial cell ratioscan be explained by mechanical irritation or septicinflammation. Neutrophilia could be a sign of concurrentRAO as well. Aspiration of foreign material and bleedingcan cause an increased number of macrophages [47].Horses with dorsal displacement of the soft palate hadeither high lymphocyte or high neutrophil numbersin BAL fluid, both of which might be a sign of chronic viralor bacterial infection. Chronic bacterial or viral infectionscan cause upper airway inflammation simultaneouslyand may result in impaired function of the soft palate[14,48]. In these cases, SAI might result from URTdysfunction or simply be a concurrent finding. Holcombeet al. [49] demonstrated that upper and lower airway

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Q4

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inflammations were both associated with stabling, butthere was no direct correlation between them.

We performed further ancillary diagnostic tests in 67animals but according to the inference tree method, thesetests were not necessary for grouping them reliably in 67%of cases. These methods were useful only to refine the finaldiagnosis. In all other cases (22/100), a very thorough andcomplex diagnostic workup using special laboratory testsand diagnostic imaging techniques was necessary to reachthe final diagnosis, thereby making it unachievable for thefield veterinarian.

Radiographic and ultrasonographic evaluation of thechest facilitated differentiating mainly infectious condi-tions; all of them in this group had abnormal lung patternand ultrasonographic findings. As described previously,these imaging techniques are helpful in differentiatingbetween horses in group IAD and ID [9]; however, in theabsence of clinical evidence of more extensive, infectiousdisease, thoracic radiographs neither refine nor improvethe diagnosis of IAD, but only increase diagnostic costs [50].None of the radiologic findings were pathognomonic, noteven in the ID group; thus, in each case, further diagnosticprocedures were necessary. Caudally displaced lungborders, increased radiolucency with concave diaphragm,and bronchiectasis were sequelae of severe RAO, asdemonstrated earlier [6,51].

Septic tracheal cytology or positive culture did notmeanthat animals could simply be grouped in the infectiousgroup. Two horses with positive culture were placed in theURTFD group based on endoscopic results, and two horseswith a secondary infection were placed in the RAO groupbased on history, clinical signs, and positive bronchodilatortest.When infections complicated the suspected RAO cases,bronchoconstriction, as one of the causes of the respiratorysigns and its severity, was evaluated with the atropin test[52]. Bacteria are commonly detected in airways of horsesaffected with heaves, and in many cases these findings arecaused by impaired clearance as a result of RAO [2,53,54].Further, infectious cases could be identified on the basis ofserology and PCR, but hematology did not prove to bereliable. Blood gas parameters did not differ significantlybetween groups, being quite useful for evaluating theevolution stage of the inflammatory process rather than inthe diagnostic workup [55].

Finally, 4% of the equine patients were left withouta specific diagnosis. In such cases, conclusions were drawnfrom the response to different treatment protocols. In twocases, we had contradictive results with history and clinicalsigns being typical for RAO but BAL cytology showing a lownumber of neutrophils. These horses improvedwith steroidtreatment. These cases could be horses suffering from RAOin remission but because they did not fulfill the criteria ofRAO definition, we had to handle them separately. This alsopoints out the fact that horses with RAO in remission aredifficult to evaluate and final diagnosis can only be basedon the characteristic history and clinical signs. There werecases resembling ID, but all cytology, cultures, serology, andPCR examinations were negative. BALF cytology showedmoderately increased neutrophil number and broncho-constriction tests were negative. They responded well forrest, anti-inflammatory, and long-term antimicrobialtreatment. In the undifferentiated cases mentioned earlier


in the text, results of further ancillary diagnostic tests werenot specific for any lower respiratory disorder. Inappro-priate staining technique might also be responsible forsome of the unidentified cases.

We did not have any primary EIPH case, probablybecause we had not got any racing Thoroughbreds forexamination and also other sports where EIPH is rathercommon, such as cutting, reining, polo, or cross-countryevent, are not widespread in Hungary. Hemosiderophageswere found in some horses with all other types of disorderssecondary to inflammation or obstruction of the airways.Frequent concurrent finding of hemosiderophages in BALFand tracheal mucopurulent secretion had earlier beendemonstrated and supports the hypothesis of correlationbetween EIPH and lower airway inflammation [56,57].

The single chronic interstitial lung disease diagnosedwas the equine multinodular pulmonary fibrosis, butbecause equine herpes virus 5 was detected with PCR, inthis case we classified it as ID. Other chronic interstitiallung diseases were not identified, thus, they seem toaccount for minimal percentage of respiratory cases.

5. Conclusions

We recorded that first opinion veterinary surgeonsinfrequently use ancillary diagnostic techniques wheninvestigating chronic lower airway disorders. We concludethat taking the history and performing a clinical examina-tion are not sufficient to establish a final diagnosis in thesecases. Number of successful diagnostic workup in the fieldwould be higher if first opinion veterinarians used RTendoscopy and broncholaveolar lavage as basic diagnostictools in all chronic respiratory cases. These ancillary diag-nostic procedures are easily performed in stable circum-stances as well. Although tracheal secretions and bloodsamples are more easily collected, results of TS Qcytologyand hematology are less informative. Culturing tracheallavage samples might add to the final diagnosis but resultscannot be evaluated easily because secondary infectionscan complicate primary non-ID and false negative culturesmay also occur.

We also concluded that establishing a diagnosis instable circumstances is impossible in approximately one-quarter of cases, and it is still challenging in clinicalsettings.

It is also noteworthy that RAO appears to be widespreadin Hungary, accounting for more than half of chronicpulmonary disorders. Finally, contrary to the current pub-lished data, it interestingly occurs mainly during the warmseason. The high outdoor dust, air-borne mold, and pollenlevels, and the necessary hay supplementation on pasturesduring the warm months complicate the optimalmanagement of horses with RAO and commonly induceexacerbations in this period of the year.

Acknowledgments

The authors thank the referring veterinarians and all oftheir colleagues from the Clinic for Large Animals for theircontributions and assistance. Special thanks are given toTimea Dufek for helping with the paperwork and keeping

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the files updated and Veronika Kokai for preparing for allthe diagnostic procedures.

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