Biclonal gammopathy associated with immunoglobulin A in a dog with multiple myeloma.

A 10-year-old neutered male Airedale Terrier was evaluated for inappetance, weight loss, and lameness. Multiple myeloma was diagnosed based on bone marrow plasmacytosis, multiple lytic bone lesions, and hyperglobulinemia with a clonal gammopathy on serum protein electrophoresis. Splenic plasmacytosis, and retinal lesions consistent with hyperviscosity syndrome also were found. Temporary responses to 2 different chemotherapy protocols (melphalan and prednisone, and cyclophosphamide and prednisone) were seen, with remission of clinical signs and a decrease in the biclonal gammopathy but no resolution of the splenic mass. Eventual return of clinical signs led to euthanasia at 175 days postdiagnosis. Necropsy examination confirmed multiple myeloma involving bone marrow and spleen, and glomerulonephritis. An immunoglobulin-A (IgA) gammopathy was demonstrated by immunoelectrophoresis; biclonality was ascertained by immunofixation electrophoresis. The clonal components consisted of intact Ig with heavy chain of the alpha class and light chain of an undetermined class. To our knowledge, this is the first report of undimerized biclonal gammopathy in a dog caused by a single heavy chain class involving IgA.