Waldenstrom's Macroglobulinemia in a Normoproteinemic Dog with Atypical Bimorphic Plasmacytoid Differentiation and Monoclonal Gammopathy

A 2-year-old neutered female Small Munsterlander dog was presented for an insect bite. Physical examination revealed a poor body condition, a peripheral lymphadenomegaly, and suspected splenomegaly. A complete blood count (Sysmex XN-V) revealed marked leukocytosis with lymphocyto-sis and abnormal dot plots. An abnormal monomorphic lymphoid population and marked rouleaux formation were noted on the blood smear. Lymph node aspirates contained an atypical bimorphic population of lymphocytes, either with a plasmacytoid or a blastic appearance. This double population was also found in the spleen, liver, bone marrow, tonsils, and other tissues. Peripheral blood and lymph node clonality assays revealed clonal BCR gene rearrangement. Flow cytometry revealed a mixed population of small-sized B-cells (CD79a+ CD21+ MHCII+) and medium-sized B-cells (CD79a+ CD21- MHCII-) in lymph nodes and a dominant population of small-sized mature B-cells (CD21+ MHCII+) in peripheral blood. Though normoproteinemic, serum protein electrophoresis revealed an increased a2-globulin fraction with an atypical restricted peak, identified as monoclonal IgM by immunofixation. Urine protein immunofixation revealed a Bence-Jones proteinuria. A diagnosis of Waldenstrom's macroglobulinemia was made. Chemotherapy was initiated, but the dog was euthanized 12 months after the initial presentation due to marked clinical degradation.

Automated summary

A 2-year-old neutered female Small Munsterlander dog presented with an insect bite. Physical examination revealed poor body condition, lymphadenomegaly, and suspected splenomegaly. Blood tests showed leukocytosis, abnormal lymphoid cells, and rouleaux formation. Tissues from various organs also showed abnormal cell populations. The diagnosis was Waldenstrom's macroglobulinemia, and chemotherapy was initiated, but the dog was euthanized 12 months later due to clinical degradation.