Pericardial effusion in a dog concurrent with carcinoma of unknown primary origin

Background: Pericardial effusion (PE) due to secondary metastasis has rarely been reported in dogs. Case description: This case describes clinical signs and further diagnostics regarding metastatic carcinoma of unknown primary origin (CUP) in refractory PE of a dog. Findings/treatment and outcome: A nine-year-old, castrated male Shih Tzu dog was referred for evaluation of cough and dyspnea. On presentation, tachypnea, intermittent cough, and muffled heart sounds were noted. Thoracic radiography, electrocardiography, and echocardiography confirmed a PE. No mass lesion was detected at the heart base, aorta, or right atrium (RA). Analysis of the PE showed hemorrhagic cytology, and an idiopathic hemorrhagic PE was tentatively diagnosed. The dog responded to conservative treatment with steroid and diuretics, but the clinical sign recurred. Further evaluation with multi-detector computed tomography (MDCT) was non-diagnostic. The dog died 457 days after initial presentation. Necropsy and histopathology revealed metastatic CUP origin. Conclusion: This case illustrated a rare cause of recurrent PE in dogs.