Histologic investigation of airway inflammation in postmortem lung samples from racehorses

OBJECTIVE To describe histologic findings in the small airways during postmortem examination of actively racing horses and to quantify the degree of airway inflammation by use of a semiquantitative scoring system. SAMPLE Lung tissues obtained from 95 horses (Thoroughbreds, Standardbreds, and Quarter Horses) that had been actively racing or training. PROCEDURES 10 standardized lung sections were obtained during postmortem examination of 37 horses that had been actively racing or training, and 2 histologic sections of the caudodorsal lung lobes previously collected from each of 58 horses that died or were euthanized during racing or training were also obtained. Sections were evaluated by use of a validated histologic small airway scoring system. RESULTS Scores for inflammatory cells, smooth muscle, and hemosiderin typically were high. Signalment and cause of death were not significant predictors of lung scores. Lung sample location was a significant predictor, with the highest scores in the caudal and dorsal sections. Inflammatory cell infiltration in peribronchiolar tissues, smooth muscle hyperplasia, and hemosiderin (prevalence of 86%, 98%, and 80%, respectively) were common findings in lungs of these horses, with the caudodorsal regions more severely affected. Correlation was moderate between smooth muscle hyperplasia and inflammatory cell infltration, with minimal correlation between hemosiderin and inflammatory cell infiltration. CONCLUSIONS AND CLINICAL RELEVANCE Inflammatory airway disease has been identified by use of bronchoalveolar lavage in young athletic horses throughout the world. In the study reported here, pathological changes were detected in the wall of small airways of horses that were actively training or racing.