Clinical Research Abstracts of the British Equine Veterinary Association Congress 2015.

Abstract: Pleural effusion (PE) is reported to occur most commonly secondary to bacterial pneumonia or lung abscesses, with neoplastic effusions contributing the minority of cases. The majority of these reports originate from America and Australia, where long distance transport of horses, a recognised risk factor, appears to occur more frequently. Anecdotally, neoplastic PE is more commonly diagnosed in the UK. Objective: To describe the causes of PE in horses resident in the UK, and to identify potential markers that can help differentiate between infectious and neoplastic causes of PE. Methods: Retrospective clinical study. Methods: Medical records from 4 referral hospitals in southern England were searched for horses diagnosed with PE. Information gathered from medical records included signalment, diagnosis (infectious vs. neoplastic), admission physical examination and biochemical findings, and characteristics of the effusion (volume, cell count, total protein [TP] concentration). Statistical comparisons were made between the neoplastic and infectious group using appropriate testing. Results: Seventy horses were identified, of which 28 (40%) were neoplastic and 42 were infectious. Horses with infectious effusions were significantly younger (median 7 vs. 13 years; P = 0.002) and had significantly smaller volumes of pleural fluid drained at admission (9.8 vs. 32.3 l; P<0.001). Horses with infectious PE had a significantly higher rectal temperature (38.6 vs. 38.2°C; P = 0.03), fibrinogen concentration (7.8 vs. 5.7 g/l; P = 0.02) and serum amyloid A concentration (223 vs. 104 mg/l; P = 0.02). Pleural fluid characteristics identified a significantly greater cell count and TP concentration in horses with infectious PE (47 x 10(9)/l vs. 3.4 x 10(9)/l; P<0.001; 54 vs. 31 g/l; P = 0.001). Conclusions: These results suggest that in the UK neoplastic effusions account for a greater proportion of PE than previously reported. A large volume of PE in an older horse with a low cell count and TP concentration should increase the index of suspicion of neoplasia. Ethical animal research: This was a retrospective study of clinical cases. Explicit owner informed consent for inclusion of animals in this study was not stated. Background: None. Competing interests: None declared.