Waldenström's macroglobulinemia (lymphoplasmacytic lymphoma) is a variant B-cell IgM-producing lymphoma of older dogs.
The World Health Organization classification defines Waldenström's macroglobulinemia as lymphoplasmacytic lymphoma with bone marrow involvement and an IgM monoclonal gammopathy of any concentration. In humans, deletion of the long arm of chromosome 6, trisomy 4 and 13q14 and 17p13 deletion are the most common abnormality associated with this disease, with up to 50% of patients having the genetic abnormality, emphasizing a genetic underpinning to the etiology of this disease.
In dogs, symptoms can be due to infiltration of bone marrow and other tissue sites by malignant lymphoplasmacytic cells or due to the effects of elevated serum IgM levels.
Clinical signs include gradual weight loss, lethargy, retinopathy, epistaxis, cutaneous masses, anemia, proteinuria and hemorrhagic diarrhea.
Unlike other forms of lymphoma, lymphadenopathy is not a consistent finding.
Hematologically, these dogs present with varying degrees of anemia, lymphopenia, neutropenia, rouleaux formation, marked hyperglobulinemia and normoalbuminemia, hypercalcemia, markedly increased serum urea concentration and prolonged thrombin time. Secondary hyperviscosity syndrome is a consistent finding and peliosis hepatis may be observed.
Diagnosis usually requires bone marrow biopsy, showing a propensity of small lymphocytes, lymphoplasmatoid cells and plasma cells within the marrow matrix at different stages of maturation.
Electrophoresis of serum or urine protein is usually confirmatory for a monoclonal IgM gammopathy.
Although a cure is unlikely, the prospect of the animal having a fairly normal, healthy life for an extended period of time (over a year in the majority of cases) is good.
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