Association between cytology and endoscopy of guttural pouches: a prospective study on 173 horses.

BACKGROUND: Guttural pouch (GP) disorders are clinically important in horses, yet the relationship between endoscopic findings and GP cytology remains poorly defined. HYPOTHESIS/OBJECTIVES: To establish reference cytological values for GP lavage fluid in horses and to investigate associations between inflammatory cytology and endoscopic findings. ANIMAL: Asymptomatic racing horses sampled in the field and horses referred for investigation of respiratory disorders. METHODS: Prospective cross-sectional study. Horses underwent clinical examination, upper airway endoscopy, and bilateral transendoscopic GP lavage. A GP inflammation score (0-15) was developed based on endoscopic appearance in the GP. Cytology was performed on GP pooled samples. Control horses were defined by the absence of clinical, hematologic, microbiological, and endoscopic abnormalities. Associations were analyzed using nonparametric tests. RESULTS: A total of 173 horses were included, of which 19 were controls. Control GP fluid cytology exhibited no or rare cells (median 30 cells/mm3; range 10-90) which were either neutrophils, macrophages, or lymphocytes. The remaining 154 horses were classified as "abnormal" (ABN) and subdivided into 2 groups according to GP fluid neutrophil proportions: group ABN1 (<1% neutrophils, n = 101, median 30 cells/mm3; range 5-360) and group ABN2 (neutrophils ≥ 1%, n = 53, median 100 cells/mm3; range 30-600). Horses in the ABN2 group showed more frequent GP lymphoid hyperplasia, secretions, and purulent exudate than horses in ABN1. CONCLUSIONS AND CLINICAL IMPORTANCE: Cytological inflammation correlates with endoscopic evidence of GP inflammation.