Recurrent aseptic peritonitis in a dog diagnosed with peritoneal mesothelioma post-mortem

A neutered male Doberman dog was presented because of recurrent aseptic peritonitis, the cause of which was not elicited pre-mortem despite multiple attempts. The dog's condition progressed over the course of ~8 mo until he was euthanized due to declining quality of life, despite medical interventions. A diagnosis of canine mesothelioma was made on necropsy. Canine mesothelioma is rare and difficult to diagnose definitively, often relying on a combination of clinical signs, imaging, and cytopathology to support a suspected diagnosis. There is no standardized treatment, but because chemotherapy has been shown to improve survival times, early diagnosis is desirable. Prioritizing high-quality sample acquisition early in the course of disease is important to improve the chances of accurate diagnosis and earlier implementation of care. Additional research is needed to further advance our abilities to correctly distinguish canine mesothelioma from reactive mesothelial changes and other neoplasms. Key clinical message: This case report highlights persistent deficiencies in our ability to clinically evaluate and diagnose canine mesothelioma. Recommendations are made for biopsy technique to improve sample quality and, thereby, the chance of definitive diagnosis.