Prevalence and characteristics of feline pleural effusion in Khon Kaen, Thailand: A 2024–2025 study

Pleural effusion (PE) is a life-threatening condition in cats that can cause severe respiratory compromise. Identification of the underlying etiology is essential for prognosis and treatment planning. This study investigated the prevalence and characteristics of diseases associated with feline pleural effusion in northeastern Thailand. Medical records of cats diagnosed with pleural effusion at the Veterinary Teaching Hospital, Faculty of Veterinary Medicine, Khon Kaen University, Thailand, between January 2024 and January 2025 were retrospectively reviewed. Cases lacking a complete diagnostic workup were excluded. Diagnoses were confirmed using cytology or histopathology for neoplasia, echocardiography for heart disease, polymerase chain reaction (PCR) for feline infectious peritonitis (FIP), and pleural fluid analysis for pyothorax. Of 86 cats initially identified, 72 met the inclusion criteria. The most common etiologies were FIP (30.5%, n=22), lymphoma (27.7%, n=20), heart disease (22.2%, n=16), and pyothorax (18.1%, n=13) and trauma (1.38%, n=1). Cats with pyothorax (1.8 ± 1.2 years) and FIP (2.5 ± 2.0 years) were significantly younger than cats with lymphoma (4.2 ± 4.4 years) and heart disease (5.3 ± 4.3 years) (P < 0.05). Restrictive cardiomyopathy was the most common cardiac disorder (43.8%) among cats with heart disease. Bacterial culture was positive in only 23.1% of pyothorax cases. FIP was the leading cause of feline pleural effusion in this population, followed by lymphoma, heart disease, and pyothorax. These findings suggest regional differences in disease epidemiology and emphasize the importance of comprehensive diagnostic evaluation in cats with pleural effusion.