Abstract

A 10-year-old male California sea lion (Zalophus californianus) presented with a 2-month history of waxing and waning clinical signs associated with central nervous system disease (bouts of unresponsiveness, dull mentation/altered attitude, tremors, mild head tilt, mydriasis, difficulty swallowing). Serial bloodwork, radiographs, and ultrasound were unremarkable. Broad serologic testing revealed no infectious causes. Mentation improved dramatically, and clinical signs resolved with high-dose prednisone (2.5 mg/kg, PO, BID). Efforts to decrease the dose resulted in a return of clinical signs. Over the following 20 days a thrombocytopenia and severe immune-mediated hemolytic anemia (IMHA) developed. Hematocrit decreased from 46% to 12% with slide auto-agglutination and poor regenerative response. Treatment with prednisone, azathioprine (2 mg/kg, q 24 h, PO), leflunomide (4.25 mg/kg, q 24 h, PO), erythropoietin, iron, and other medications was unsuccessful in stopping progression, and the animal died.

At gross examination, abdominal and thoracic lymph nodes were markedly enlarged and effaced by a pale tan, soft, and friable mass. Histologic and immunohistochemical findings confirmed advanced, disseminated multicentric B-cell lymphoma. Altered mentation was attributed to neoplastic dissemination throughout the meninges and superficial cerebral cortex. Blood cell breakdown likely occurred in the tumors, bone marrow, and vasculature secondary to neoplastic invasion. IMHA and thrombocytopenia was compounded by myelophthisis and direct blood loss from a large necrotic mesenteric tumor. Gastric ulceration (despite prophylactic famotidine and sucralfate) was present, presumably related to corticosteroid administration. Leflunomide drug levels were tested and found to be in therapeutic range, suggesting it could be of benefit for adjunctive therapy of primary IMHA in this species, despite the poor success in this case of secondary IMHA.

Acknowledgments

The authors thank the dedicated marine mammal staffs at Brookfield Zoo and Oceans of Fun for their dedication to this case.