Correlation of clinical score, intrapleural pressure, cytologic findings of bronchoalveolar fluid, and histopathologic lesions of pulmonary tissue in horses with summer pasture-associated obstructive pulmonary disease

Lais R. Rodrigues Costa Department of Veterinary Clinical Sciences, School ofVeterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Thomas L. Seahorn Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.
Present address is Hagyard-Davidson-McGee Associates, Medicine, 4250 Ironworks, Lexington, KY, 40511-8412.

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Rustin M. Moore Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Henry W. Taylor Veterinary Pathology, School ofVeterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Stephen D. Gaunt Veterinary Pathology, School ofVeterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Ralph E. Beadle Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Abstract

Objective—To correlate clinical score, intrapleural pressure, cytologic findings of bronchoalveolar lavage fluid (BALF), and histologic lesions of pulmonary tissue in horses affected with summer pasture-associated obstructive pulmonary disease (SPAOPD).

Animals—8 adult horses affected with SPAOPD and 6 adult horses without evidence of respiratory tract disease.

Procedure—Clinical score, change in intrapleural pressure (ΔPpl) during tidal breathing, results of cytologic examination and bacteriologic culture of BALF, and results of histologic examination of pulmonary parenchyma were evaluated.

Results—Clinical scores for SPAOPD-affected horses (median, 5.75; range, 4.0 to 7.5) were significantly greater, compared with clinically normal horses (median, 2.0; range, 2.0 to 3.0). Cytologic examination of BALF from SPAOPD-affected horses revealed predominantly nondegenerate neutrophils. Histologic lesions were identified throughout pulmonary tissue and included severe accumulation of mucus and neutrophils within the small airways, metaplasia of bronchiolar goblet cells, and mild peribronchial infiltrate. Histologic examination of specimens collected via percutaneous biopsy was predictive of disease and corresponded to findings at postmortem examination. Clinical score and δPpl were highly correlated with mucus accumulation in the airways of affected horses. Peribronchial inflammatory infiltrate correlated with percentage of neutrophils in BALF of affected horses.

Conclusions and Clinical Relevance—Clinical scoring and ΔPpl provided valid estimates of disease severity. Findings from cytologic examination of BALF of SPAOPD-affected horses varied, although, in most instances, it was diagnostically useful. Severe mucus accumulation in the airways was the most remarkable histopathologic finding in SPAOPDaffected horses. Examination of biopsy specimens collected from pulmonary parenchyma was consistently useful in diagnosing SPAOPD. (Am J Vet Res 2000;61:167–173)

Abstract

Objective—To correlate clinical score, intrapleural pressure, cytologic findings of bronchoalveolar lavage fluid (BALF), and histologic lesions of pulmonary tissue in horses affected with summer pasture-associated obstructive pulmonary disease (SPAOPD).

Animals—8 adult horses affected with SPAOPD and 6 adult horses without evidence of respiratory tract disease.

Procedure—Clinical score, change in intrapleural pressure (ΔPpl) during tidal breathing, results of cytologic examination and bacteriologic culture of BALF, and results of histologic examination of pulmonary parenchyma were evaluated.

Results—Clinical scores for SPAOPD-affected horses (median, 5.75; range, 4.0 to 7.5) were significantly greater, compared with clinically normal horses (median, 2.0; range, 2.0 to 3.0). Cytologic examination of BALF from SPAOPD-affected horses revealed predominantly nondegenerate neutrophils. Histologic lesions were identified throughout pulmonary tissue and included severe accumulation of mucus and neutrophils within the small airways, metaplasia of bronchiolar goblet cells, and mild peribronchial infiltrate. Histologic examination of specimens collected via percutaneous biopsy was predictive of disease and corresponded to findings at postmortem examination. Clinical score and δPpl were highly correlated with mucus accumulation in the airways of affected horses. Peribronchial inflammatory infiltrate correlated with percentage of neutrophils in BALF of affected horses.

Conclusions and Clinical Relevance—Clinical scoring and ΔPpl provided valid estimates of disease severity. Findings from cytologic examination of BALF of SPAOPD-affected horses varied, although, in most instances, it was diagnostically useful. Severe mucus accumulation in the airways was the most remarkable histopathologic finding in SPAOPDaffected horses. Examination of biopsy specimens collected from pulmonary parenchyma was consistently useful in diagnosing SPAOPD. (Am J Vet Res 2000;61:167–173)

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