Multiple Myeloma in a Dog

Abstract

Background: The multiple myeloma is a neoplasia characterized by the uncontrolled proliferation of plasma cells (plasmacytes) in the bone marrow and in other tissues. The infiltration of the neoplasia cells associated to the high level of anomalous immunoglobulin production (M protein) results in a variety of clinic-pathologic anomalies. It is a rare disease in dogs, corresponding to 0.3% of all malignant neoplasia and 2% of the hematopoietic, with few literature descriptions. So, the present paper aims at properly report a multiple myeloma in a dog of non-defined breed, emphasizing the clinic, laboratorial, radiographic and pathologic aspects.

Case: In a Veterinary Teaching Hospital, an 11-year-old dog of non-defined breed was admitted, weighing 10.8 kg of body mass. The clinic history was claudication of the right thoracic member, hyporexia and lethargy in the past 20 days. The main abnormalities in the physical examination were holosystolic cardiac murmur III/VI on mitral focus, and high sensibility to touch in the right humerus. Laboratory tests showed pancytopenia, serum hypercalcemia and Bence-Jones proteinuria. Radiographic examination confirmed polyostotic punctate osteolysis on the right humerus; pelvic, femurs and vertebrae bones from L2 to L7, on generalized condition. Cytology by aspiration puncture from the left femur marrow bone did not confirm neoplasia cells. The clinic condition of the referred animal was progressively getting worse and euthanasia was performed. At the dog’s necropsy it was spotted tumor infiltrations on the femur, the humerus and the vertebrae canal. Histopathological exam of the bone marrow revealed diffuse occupation by distinguished plasmacytes, in some áreas reaching around 100% of cell population. Metastases on the primary tumor were found on the liver, kidney and spleen.

Discussion: The diagnosis of multiple myeloma in this dog was confirmed by bone marrow histopathological exam. It is confirmed when there is more than 20% of plasmacytes in the examined structure. In this report, certain areas were spotted with 100% occupation of neoplasia cells. On the other hand, the first cytological assess did not reveal any abnormalities, suggesting that the place which received the puncture (aspiration) was not infiltrated by tumor cells. It is described that in the bone marrow may occur grouping of plasmacytes, as it was observed the animal’s necropsy of this report. This aspect point out that the diagnosis cannot be discarded only with a negative cytological exam from the bone marrow; especially if there are clinic, laboratorial and radiographic signs compatible to the illness. The spotted clinic signs by this patient are frequent in dogs with multiple myeloma, as well as the laboratory results, except to the monoclonal gammopathy. Due to a no realization of electrophoresis, this abnormality cannot be confirmed. At the initial assessment of the disease, the radiographic exam is considered golden standard as it was observed in this dog. The radiographic abnormalities were determinant, once they conducted the diagnosis towards the suspected neoplasia. According to current diagnosis criteria, on this present case, the pancytopenia, serum hypercalcemia and Bence-Jones proteinuria also helped towards the suspicion of multiple myeloma. However, the evaluation of the bone marrow was decisive to the final diagnosis; and a special attention was given to puncture more than one place in the bone marrow, which improved/enhanced the diagnosis possibility in this patient.

Keywords: plasma cells, bone marrow, pancytopenia, osteolysis, radiography.