A two-year-old, male neutered, domestic longhaired cat presented to the Cornell Emergency Service for evaluation of lethargy, intermittent inappetence, and increased respiratory effort. On presentation he was open-mouth breathing, tachycardic (240 bpm), hyperthermic (103.6F), and mildly muscle wasted along the spine, with a grade 4/6 parasternal systolic heart murmur. Thoracic focused assessment with sonography for trauma (T-FAST) revealed a moderate amount of pleural effusion and a normal left atrium:aorta ratio. Abdominal focused assessment with sonography for trauma (A-FAST) revealed scant abdominal fluid. He had a moderate anemia (HCT 26%) and hyperproteinemia (9.4 g/dL). A therapeutic thoracocentesis of the right pleural space was performed and approximately 25 mL of yellow, viscous fluid was removed. A Rivalta test was performed on peritoneal effusion and a positive result was obtained, suggestive of a high-protein exudate, which was confirmed with fluid analysis. This exudate was further characterized as a sterile pyogranulomatous exudate via cytology, consistent with feline infectious peritonitis (FIP). A serum ELISA to test for coronavirus antibodies confirmed the presence of coronavirus in the patient.

To rule out a neoplastic cause of the bicavitary effusion and to look for evidence of lesions consistent with FIP, an abdominal ultrasound was performed. A mottled spleen and enlarged jejunal lymph node were identified and aspirated. Cytologic analysis of these aspirates showed granulomatous inflammation in both tissues, which further supported a diagnosis of FIP. An abbreviated echocardiogram was performed to definitively rule out congestive heart failure as the cause of the bicavitary effusion and to assess the risk of initiating steroid treatment. Though a thickened left ventricle and turbulent flow through the aortic valve were identified, the size of the left atrium was within normal limits, ruling out congestive heart failure.

The current gold standard for diagnosing FIP is to obtain a biopsy sample of affected tissue for histopathology and immunohistochemistry to look for coronavirus within characteristic pyogranulomatous lesions. Given the amount of evidence consistent with FIP and the invasiveness of this procedure, the owner decided not to pursue this diagnostic test. The patient became increasingly lethargic in hospital and his pleural effusion recurred. Euthanasia was elected at this time given the severity of his condition and poor prognosis.