Abstract
A 10-year-old, entire male, English Springer Spaniel was referred for evaluation of weight loss, polyuria, polydipsia and gastrointestinal tract signs including melena/haematochezia for the previous six months. Results of serum protein electrophoresis, urine analysis, computed tomography of the thorax/abdomen, bone marrow aspiration and core biopsy, and splenic and mesenteric lymph node cytology were consistent with multiple myeloma. Endoscopically obtained gastrointestinal tract biopsies identified marked plasma cell infiltration within the duodenum, ileum and colon; immunohistochemistry showed positive labelling to MUM1 and Lambda confirming clonal plasma cell involvement. The dog entered complete clinical remission seven weeks after starting a melphalan/prednisolone protocol. The dog was euthanised 475 days after starting treatment due to cervical pain and collapse. At the time of euthanasia, blood work was not supportive of a relapse of multiple myeloma. To the authors' knowledge, this is the first report of multiple myeloma involving the gastrointestinal tract in a dog.