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

Overview

• This study aimed to understand the relationship between cytological analysis of guttural pouch lavage fluid and endoscopic findings in horses, establishing reference values and investigating inflammation markers.
• It involved examining healthy and clinically abnormal horses to correlate inflammation observed under endoscopy with cytology results from guttural pouch fluid.

Background

• The guttural pouches (GP) are unique anatomical structures in horses that can harbor important clinical disorders, often linked to respiratory health.
• Diagnosing GP disorders involves endoscopic examination and sometimes cytological evaluation of fluid obtained from the pouches.
• Before this study, there was a lack of clear understanding or established reference values correlating endoscopic appearance with cytological findings in horses’ guttural pouches.

Study Objectives

• To establish normal baseline cytological values for the lavage fluid from equine guttural pouches in healthy horses.
• To investigate associations between the degree of inflammation detected cytologically and endoscopic signs of GP inflammation.

Methodology

• The study was designed as a prospective cross-sectional study involving 173 horses of two types:
  • Asymptomatic racing horses sampled in the field (healthy controls).
  • Horses referred for investigation of respiratory disorders (clinical cases).
• Each horse underwent:
  • Clinical examination.
  • Upper airway endoscopy, focusing on guttural pouches.
  • Bilateral transendoscopic guttural pouch lavage to collect fluid samples.
• An inflammation scoring system from 0 to 15 was developed to score the endoscopic appearance of the GP.
• Cytology was performed on pooled lavage fluid samples from both guttural pouches of each horse.
• Control horses were selected based on absence of clinical signs, normal blood and microbiological exams, and normal endoscopy.
• Statistical associations were examined primarily using nonparametric analytical methods suited for the data distributions.

Results

• The total sample included:
  • 19 control horses with no abnormalities.
  • 154 horses classified as “abnormal” based on clinical or endoscopic findings.
• Key findings for control horses:
  • GP lavage fluid contained very few cells (median 30 cells/mm³), indicating little inflammation.
  • Cell types were mainly neutrophils, macrophages, or lymphocytes, but numbers were low and within normal variation.
• Abnormal horses were further subdivided into two groups based on percentage of neutrophils in GP fluid:
  • Group ABN1: <1% neutrophils (101 horses), median 30 cells/mm³. These horses had relatively low cellularity similar to controls but with some abnormalities.
  • Group ABN2: ≥1% neutrophils (53 horses), median 100 cells/mm³, showing significant inflammatory cell infiltration.
• Comparisons revealed horses in ABN2 (higher neutrophils) exhibited:
  • More frequent lymphoid hyperplasia in GP as seen endoscopically.
  • Presence of secretions and purulent exudate in the pouches.

Conclusions

• There is a clear correlation between cytological inflammation (especially neutrophil proportion) and visual endoscopic evidence of GP inflammation.
• The study established reference cytological values for GP lavage fluid in healthy horses, which helps differentiate normal from abnormal inflammatory states.
• These findings support the use of GP lavage cytology alongside endoscopy in the diagnosis and monitoring of guttural pouch disorders.
• The inflammation score and cytology together may improve clinical assessment and management of respiratory and GP-related diseases in horses.

Implications for Veterinary Practice

• Veterinarians can use endoscopy combined with GP lavage cytology to detect and monitor guttural pouch inflammation more accurately.
• Reference cytology values provide a baseline to identify when inflammation is present, aiding in early diagnosis.
• The study supports a minimally invasive approach that can be performed in the field, useful for both healthy racing horses and those with clinical respiratory issues.