Synovial extramedullary hematopoiesis in a dog.

Synovial extramedullary hematopoiesis is a rarely reported condition in humans and, to date, has never been reported in canines. This case report describes the clinical presentation, diagnostic work-up, treatment, and outcome of a canine case confirmed to have hematopoietic tissue within multiple joints. A client-owned canine. The clinical presentation was most consistent with immune-mediated polyarthritis, and arthrocentesis was performed in multiple joints for cytological evaluation and culture. Cytology revealed evidence of extramedullary hematopoiesis, and shortly thereafter the dog was diagnosed with immune-mediated hemolytic anemia and thrombocytopenia. Pregabalin, prednisolone, clopidogrel, and cyclosporine were started, and after several recheck appointments and dose adjustments, the dog's clinical signs resolved for all conditions. Unusual sites of extramedullary hematopoietic tissue may result in a clinical presentation for which more traditional etiologies and differentials are not applicable.