A Longitudinal Analysis of Equine Asthma Presentation and Response to Treatment Using Lung Function Testing and BAL Cytology Analysis in Combination with Owner Perception

SIMPLE SUMMARY: Equine asthma (EA), a chronic non-infectious inflammatory disease of the lower airways, is a pervasive and important cause of poor respiratory health in horses. The clinical presentation ranges from mild decrements in peak performance to crippling respiratory impairment. Horses with severe equine asthma may be diagnosed and effectively treated using clinical scoring alone, but more subtle disease often requires lung function testing and cytologic evaluation of lower airway respiratory secretions (via bronchoalveolar lavage, BAL) in order to arrive at a correct diagnosis and allow for the best treatment. Published data are lacking to describe the longitudinal course of disease, as characterized by a pulmonary specialty clinic along with owner descriptions. This study examines horses with at least two visits to a specialty pulmonary clinic for evaluation of EA, describes and quantifies the types and range of clinical presentations that fall under the umbrella term of EA in horses in New England, considers the reliability of owner perception of horses clinical signs through a newly developed owner complaint score, and documents and assesses the diagnostic methods used at the Tufts Cummings School of Veterinary Medicine, as well as the response of horses with EA to treatment and time. ABSTRACT: (1) Background: Equine asthma (EA) is a pervasive and important cause of poor performance and respiratory morbidity in horses. Diagnosis of EA includes an owner complaint, clinical scoring, lung function testing, and cytological analysis of bronchoalveolar lavage (BAL) cytology. There is a paucity of information about the longitudinal course of the disease using these outcome assessments; thus, this study sought to describe and quantify, in horses with more than one visit to a specialty pulmonary clinic in New England, the type and range of clinical presentations with an eventual diagnosis of EA. It also aimed to develop and compare the outcomes of scoring systems for owner complaints and veterinary assessments, document and assess the diagnostic methods used, and evaluate the response of the horses to treatment and time. (2) Methods: This study was a retrospective, cross-sectional, STROBE-compliant observational analysis of equine patients who visited the Tufts Cummings Hospital for Large Animals (HLA) for evaluation of equine asthma (EA) from 1999–2023. The horses were categorized as having mild–moderate (mEA) or severe EA (sEA) using the ACVIM consensus statement guidelines. After excluding those with inadequate documentation or only one visit (n = 936), a total of 76 horses were included in the study. Of the 197 visits, 138 (70.0%) resulted in a diagnosis of mEA and 45 (22.8%) resulted in a diagnosis of sEA. Demographic information, owner complaints, clinical examination and scoring, lung function testing, BAL cytology, and recommendations for environmental remediation and pharmacologic treatment were recorded for all the visits. The data were analyzed for agreement between owner complaints (complaint score, CS) and clinical examination findings (examination score, ES), changes in CS and ES, lung function testing, and BAL cytology over time, with 197 visits recorded. (3) Results: A comparison between the CS and ES showed that the owners were more likely than veterinarians to detect cough, and a decrease in cough was the most common owner observation after treatment. The response to the histamine challenge, used to detect airway hyperreactivity, was significantly improved with treatment or time in the horses with mEA, whereas baseline lung function did not significantly change in mEA or sEA. (4) Conclusions: Owners can be astute observers of clinical signs, especially cough, in EA. Tests of airway hyperreactivity are more successful in detecting changes in mEA than are baseline lung function testing and assessment of BAL cytology.