Endobronchial biopsy scores reflect the severity of naturally occurring equine asthma

Introduction:

Equine asthma (EA) is a common inflammatory airway disease, where persistent inflammation provokes the airways to undergo unfavorable structural changes. The aim was to investigate the association of naturally occurring EA disease severity and airway remodeling.

Materials and Methods:

Control horses (n = 15) and horses with mild/moderate EA (MMEA, n = 10) or severe EA (SEA, n = 5) were examined in a prospective clinical case-control study. Clinical examination, arterial blood oxygen content (PaO2), endoscopy, and airway cytology from tracheal wash (TW) and bronchoalveolar lavage (BAL) were performed. Endobronchial biopsies (EBB) were obtained 25cm distally from the main carina, stained for routine histology and scored with a system using 14 maximum points1. The results were analyzed with ANOVA and Pearson correlation coefficient.

Results:

Mean (±SD) EBB score for control horses was 6.9 (±2.2), for MMEA horses 7.3 (±2.0) and for SEA horses 9.2 (±1.3). The EBB score was different between control and SEA horses (p=0.033), but not between control and MMEA horses (p=0.601), or MMEA and SEA horses (p=0.095). EBB score correlated positively with BAL neutrophil-% (r=0.409, p=0.025) and negatively with PaO2 (r=–0.457, p=0.011). PaO2 was different between control and SEA horses (p=0.041). BAL neutrophil-% for control horses was 1.9% (±0.9), for MMEA horses 11.3% (±4.7) and for SEA horses 39.1% (±12.9). Differences between groups were observed in BAL neutrophil-%, BAL macrophage-%, TW neutrophil-% (p<0.001), and BAL lymphocyte-% (p=0.013).

Conclusion: In this spontaneous asthma model, airway remodeling was associated with SEA, while EBB could not differentiate horses with MMEA from control horses. Remodeling and severe neutrophilic airway inflammation reflected impaired oxygen transfer from the alveoli into blood.

References:

1. Bullone, M., Hélie, P., Joubert, P. and Lavoie, J.-P. (2016), Development of a Semiquantitative Histological Score for the Diagnosis of Heaves Using Endobronchial Biopsy Specimens in Horses. J Vet Intern Med, 30: 1739-1746.