Extramedullary (gastric) plasmacytoma in a dog
Rebecca Gans, Felipe Reggeti, Kevin Finora, Kimberly Ho
Animal Health Laboratory, University of Guelph, Guelph, ON (Reggeti); Central Toronto Veterinary
Referral Clinic, Toronto, ON (Gans, Finora, Ho)
AHL Newsletter 2020;24(4):21.
An 8-year-old female spayed Shi Tzu presented for evaluation of intermittent vomiting and diarrhea. A complete blood count (CBC) demonstrated a mild non-regenerative anemia (PCV 33%) and a serum biochemistry noted moderate hyperkalemia (5.7 mmol/L), moderate hypoalbuminemia (18 g/L), and marked hyperglobulinemia (60 g/L). Spec cPL, cobalamin, and folate were all found to be within normal reference intervals. No ova or parasites were seen in the fecal sample. An ACTH stimulation test ruled out hypoadrenocorticism. Urinalysis was unremarkable.
An abdominal ultrasound demonstrated a 3.6 cm x 2.9 cm heterogeneous mass of the gastric wall, gastric lymphadenopathy, and scant ascites. The finding of a mass with regional lymphadenopathy was suggestive of metastatic malignant neoplasia. The packed cell volume (PCV) had decreased to 23%. Ultrasound guided - fine needle aspirates (FNA) of the gastric mass and the enlarged gastric lymph nodes were collected and submitted to the Animal Health Laboratory, University of Guelph, for cytological evaluation. Examination of the smears from both aspirated tissues demonstrated a monotypic population of plasma cells with 4-fold anisocytosis and 2-fold anisokaryosis (Fig. 1). The cells contained moderate quantities of basophilic cytoplasm, distinct paranuclear clearing and eccentrically located, round to oval nuclei with coarsely clumped chromatin and no visible nucleoli. Binucleated cells and mitotic figures were frequently identified. Some of these cells contained globular cytoplasmic inclusions composed of immunoglobulins (Russell bodies), compatible with Mott cells. These findings were consistent with a diagnosis of extrameduallary (gastric) plasmacytoma with spread to the regional lymph nodes.
Urine was submitted for Bence-Jones proteinuria, and blood was collected for PCV re-assessment and serum protein electrophoresis. The PCV had declined further to 18%. The urine was positive for Bence-Jones proteins, indicating the presence of the light chain portion of the increased M component of the immunoglobulin (1, 2). The protein electrophoresis results (Fig. 2) indicated marked progressive hyperglobulinemia (72g/L) and relative (compensatory) hypoalbuminemia (18g/L.) The hyperglobulinemia was characterized by increased gamma globulins, outlined by a narrow-based peak, consistent with a monoclonal gammopathy.
A diagnosis of multiple myeloma may be established when 2 of the following 4 criteria are met:
1) monoclonal gammopathy, 2) Bence-Jones proteinuria, 3) 20% infiltration of the bone marrow, liver, or spleen by plasma cells, and 4) punched-out bony lesions evident on radiographs (3). The serum protein electrophoresis, Bence-Jones protein urine test, and cytology results satisfied criteria 1, 2, and 3; however, since infiltration of the bone marrow with neoplastic plasma cells could not be investigated in this case, a diagnosis of extramedullary (gastric) plasmacytoma with metastasis to regional lymph nodes was preferred.
Treatment with the chemotherapeutic drug melphalan along with prednisone (4) was recommended. The long-term prognosis for multiple myeloma is generally good in dogs treated with this protocol, resulting in a median survival time of 540 days (4). Using this therapy, 43% of dogs achieved complete remission, 49% achieved partial remission, and only 8% showed no response (3). However, as this patient displayed multiple negative prognostic factors, the long-term prognosis was poor (3), and the owner opted for euthanasia. AHL
Figure 1. Gastric mass aspirate showing a monotypic population of neoplastic plasma cells with increased mitotic activity (arrows) and intracytoplasmic Russell bodies (arrowhead). Wright’s (400X)
Figure 2. Serum protein electrophoresis. The discrete band at the bottom of the cellulose acetate strip (upper right) is represented by a narrow-based peak in the gamma globulin region of the densitogram, consistent with a monoclonal gammopathy.
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2. Giraudel, JM, Pages J and Guelfi J. Monoclonal gammopathies in the dog: A retrospective study of 18 cases (1986-1999) and literature review. JAAHA 2002;38(2):135-47.
3. Liptak JM, Thamm DH and Vail DM. Multiple Myeloma. In: Withrow & MacEwen's Small Animal Clinical Oncology, 6th ed. Vail D, Thamm, D and Liptak J, eds. Elsevier, 2020:740-752.
4. Fernández R. and Chon E. Comparison of two melphalan protocols and evaluation of outcome and prognostic factors in multiple myeloma in dogs. J Vet Intern Med 2018;32(3):1060–1069.