Retrospective analysis of pleural effusion in cats

Pleural effusion is a common presenting cause for feline patients in small animal practice. The objectives of this study were to identify possible correlations between the aetiology of effusion and clinical and laboratory findings.

In this retrospective study of 306 cats diagnosed with pleural effusion of established aetiology, cats were divided into six major groups: cardiac disease (CD), feline infectious peritonitis (FIP), neoplasia, pyothorax, chylothorax and miscellaneous. Clinical, laboratory and radiographic parameters were compared between groups.

CD was the most common aetiology (35.3%), followed by neoplasia (30.7%), pyothorax (8.8%), FIP (8.5%), chylothorax (4.6%) and miscellaneous diseases (3.7%). In 26 (8.5%) cats, more than one underlying disease was diagnosed as a possible aetiology for pleural effusion. Cats with FIP were significantly younger than those with CD (P <0.001) and neoplasia (P <0.001). Cats with CD were presented with a significantly lower body temperature compared with cats with FIP (P = 0.022). Cats with CD had significantly higher serum alanine aminotransferase activity compared with all other cats (FIP and pyothorax, P <0.001; neoplasia and chylothorax, P = 0.02) and serum alkaline phosphatase activity compared with the pyothorax (P <0.001) and FIP groups (P = 0.04), and significantly lower protein concentrations (FIP, pyothorax and neoplasia, P <0.001; chylothorax, P = 0.04) and nucleated cell counts in the effusion than all other groups (pyothorax and neoplasia, P <0.001; chylothorax, P = 0.02; FIP, P = 0.04). The glucose level in the effusion of cats with pyothorax was significantly lower than glucose levels in patients with CD, neoplasia and chylothorax (P <0.001). Of 249 cats with a follow-up of at least 10 days, 55.8% died or were euthanased during that time.

CD and neoplasia were the most common causes for feline pleural effusion. Age, liver enzymes, as well as cell count, protein and glucose levels in the effusion can aid in the investigation of underlying aetiologies.