biostudies-literatureUnknown9(2)Wheatley MA<h4>Case summary</h4>A 10-year-old domestic shorthair cat presented for lethargy, anorexia and labored breathing. Significant pleural and pericardial effusions prompted thoracocentesis and pericardiocentesis. Cytologic evaluation of the pericardial effusion revealed a highly cellular hemorrhagic, eosinophilic (12%) effusion, with many markedly atypical suspected mesothelial cells, interpreted as concerning for neoplasia. Thoracoscopic subtotal pericardiectomy and histology of the pericardium revealed predominantly eosinophilic inflammation with multifocal mesothelial hypertrophy and ulceration. A peripheral eosinophilia was not present on serial complete blood counts. Initial infectious disease testing was mostly negative. <i>Toxoplasma gondii</i> titers were most consistent with prior exposure, although reactivation could not be excluded. The owner's medical history included a prior diagnosis of bartonellosis. Owing to the challenges of definitive <i>Bartonella</i> species exclusion, the cat was treated empirically with pradofloxacin and doxycycline, and a subtotal pericardectomy. There was improvement at first but pleural effusion recurred approximately 3 months after discharge. The cat was euthanized and a necropsy was not performed. Subsequent pericardial effusion <i>Piroplasma/Bartonella/Borrelia</i> droplet digital PCR detected DNA of <i>Bartonella vinsonii</i> subspecies <i>berkhoffii</i>, and peripheral blood culture and sequencing revealed a rare apicomplexan organism (90% homology with <i>Colpodella</i> species) of unknown clinical significance. Testing for filamentous bacteria and fungal pathogens was not performed.<h4>Relevance and novel information</h4>This case offers several unique entities - eosinophilic pericardial effusion and eosinophilic pericarditis of unknown etiology - and illustrates the well-known marked atypia that may occur in reactive and hyperplastic mesothelial cells, particularly of infrequently sampled and cytologically described feline pericardial effusion, supporting a cautious interpretation of this cytology finding.JFMS open reports20551169231213498https://www.ebi.ac.uk/biostudies/studies/S-EPMC10693801biostudies-literatureEosinophilic pericardial effusion and pericarditis in a cat.PMC10693801Stowe DMMaggi RShamoun JCullen JMBreitschwerdt EBSommer SLWheatley MAfalseEosinophilic pericardial effusion and pericarditis in a cat.<h4>Case summary</h4>A 10-year-old domestic shorthair cat presented for lethargy, anorexia and labored breathing. Significant pleural and pericardial effusions prompted thoracocentesis and pericardiocentesis. Cytologic evaluation of the pericardial effusion revealed a highly cellular hemorrhagic, eosinophilic (12%) effusion, with many markedly atypical suspected mesothelial cells, interpreted as concerning for neoplasia. Thoracoscopic subtotal pericardiectomy and histology of the pericardium revealed predominantly eosinophilic inflammation with multifocal mesothelial hypertrophy and ulceration. A peripheral eosinophilia was not present on serial complete blood counts. Initial infectious disease testing was mostly negative. <i>Toxoplasma gondii</i> titers were most consistent with prior exposure, although reactivation could not be excluded. The owner's medical history included a prior diagnosis of bartonellosis. Owing to the challenges of definitive <i>Bartonella</i> species exclusion, the cat was treated empirically with pradofloxacin and doxycycline, and a subtotal pericardectomy. There was improvement at first but pleural effusion recurred approximately 3 months after discharge. The cat was euthanized and a necropsy was not performed. Subsequent pericardial effusion <i>Piroplasma/Bartonella/Borrelia</i> droplet digital PCR detected DNA of <i>Bartonella vinsonii</i> subspecies <i>berkhoffii</i>, and peripheral blood culture and sequencing revealed a rare apicomplexan organism (90% homology with <i>Colpodella</i> species) of unknown clinical significance. Testing for filamentous bacteria and fungal pathogens was not performed.<h4>Relevance and novel information</h4>This case offers several unique entities - eosinophilic pericardial effusion and eosinophilic pericarditis of unknown etiology - and illustrates the well-known marked atypia that may occur in reactive and hyperplastic mesothelial cells, particularly of infrequently sampled and cytologically described feline pericardial effusion, supporting a cautious interpretation of this cytology finding.2023-01-01T00:00:00Z2023 Jul-Dec2025-04-25T17:30:19.701Z2025-04-06T04:05:17.288ZS-EPMC106938013805061610.1177/20551169231213498