Leishmania Infection during Chemotherapy in a Dog Diagnosed with Multicentric Large B-Cell Lymphoma—A Diagnostic Challenge

Dogs with lymphoma are at risk of developing clinical complications due to immunosuppression and side effects of chemotherapy. Clinical reports of concurrent lymphoma and leishmaniasis are rare and confined to single cases of comorbidity at presentation. Herein, we describe a case of lymphoma during maintenance chemotherapy in which bone marrow cytology showed myelodysplasia associated with leishmaniasis. The dog was a seven-year-old intact female Parson Russel Terrier with a two-week history of generalized lymphadenopathy. Diagnosis of multicentric high-grade B-cell lymphoma stage Va was carried out with cytological and cytofluorimetric assays of external lymph nodes, abdominal ultrasound, chest radiology, and lymphoid blasts blood smear examination. The dog lived and had traveled in endemic areas of Leishmania with uninterrupted prevention against sand fly bites by an insecticide-impregnated collar and presented seronegativity to Leishmania at presentation. Chemotherapy for lymphoma was successful and the patient achieved complete remission. Approximately eight months after the diagnosis, a persistent pancytopenia was assessed. Unexpectedly, Leishmania amastigotes were identified in the bone marrow. Combined treatment rounds were administered with antileishmanial and antineoplastic drugs for approximately eight months. Eventually, lymphoma relapsed and became unresponsive to chemotherapy, and the dog was euthanatized. Canine lymphoma overlapping with subsequent Leishmania infection as a complication is rare and lacks specific clinical manifestations. A delayed diagnosis of leishmaniasis may occur. We suggest considering leishmaniasis as part of the differential diagnosis of persistent pancytopenia in dogs with lymphoma, particularly in dogs who reside or travel to endemic areas, when treatment fails or abnormal laboratory findings are present.