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Bone marrow aspirate from a dog with multiple myeloma that contains many plasm cells (Wright-Leishman stain)
Radiographs of the tibia in the dog with plasmacytoma. Multifocal osteolytic puncta are noted on the tibia[1]

Plasmacytoma (Multiple myeloma, plasma cell myeloma) are a metastatic multicentric round cell neoplasm of well-differentiated B cell lymphocytes typically originating from the bone marrow.

These tumors in dogs can metastasize widely and have a predilection for flat bone, especially the spine, pelvis, ribs, skull, and proximal extremities. They have been reported less commonly as primary tumors (extramedullary) in long bones as well as the vertebrae, mandible[2], larynx[3], tongue[4], penis[5], rectum[6], cranium[7], spleen, liver[8] and stomach.

Plasmacytomas have a preponderance for overproduction of Bence-Jones proteins, an homogenous immunoglobulin (IgG[9], IgA[10] or IgM) which can mimic normal immunoglobulins, resulting in a monoclonal gammopathy on serum electrophoresis[11][12]. Some rare plasmacytomas are nonsecretory[13] but the majority are secretory, leading to hyperviscosity syndrome.

The cause(s) of plasmacytoma are not clearly established, but genetics, viral infections, chronic immune stimulation due to multiple parasites[14], and exposure to carcinogens have been identified as possible contributing factors[15].

Affected dogs can exhibit signs of lethargy, weakness, lameness, bone pain, hemorrhage (e.g, petechiae on mucous membranes, gingival bleeding, and epistaxis), polyuria / polydypsia, and/or neurologic deficits. Other presenting signs of disease may include hypertension, ophthalmic abnormalities (e.g., venous dialation with sacculation, retinal hemorrhages, and retinal detachment), neurologic dysfunction (including seizures), organomegaly, and suggestion of multiple organ failure[16].

Clinical signs and symptoms may be present for up to a year before a definitive diagnosis of multiple myeloma is made.

Diagnosis of plasmacytoma in dogs can be difficult, but a number of satellite indices are suggestive, including radiographic evidence of osteolysis, demonstration of greater than 20% plasma cells in bone marrow biopsies, a monoclonal gammopathy on serum protein electrophoresis or the presence of Bence-Jones proteinuria[17].

Multifocal radiolucent lesions within the bone may be seen in ~ 40% of dogs suffering from multiple myeloma (in contrast, osteolytic lesions rarely are seen in cats)[18].

With bone marrow biopsy, the presence of large aggregates or sheets of plasma cells within the marrow it is highly suggestive of multiple myeloma, if not diagnostic[19]. Secondary amyloidosis in affected organs has been reported[20].

Chemotherapy is the definitive treatment with over 90% of dogs treated with chemotherapy exhibit clinical improvement. However, eventual relapses are common 1 - 2 years later.

Cyclophosphamide, melphalan, doxorubicin[21], diphenhydramine and radiation therapy are commonly used[22][23].


  1. Fukumoto S et al (2012) Anaplastic atypical myeloma with extensive cutaneous involvement in a dog. J Vet Med Sci 74(1):111-115
  2. Smithson CW et al (2012) Multicentric oral plasmacytoma in 3 dogs. J Vet Dent 29(2):96-110
  3. Witham AI et al (2012) Extramedullary laryngeal plasmacytoma in a dog. N Z Vet J 60(1):61-64
  4. Ware K & Gieger T (2011) Use of strontium-90 plesiotherapy for the treatment of a lingual plasmacytoma in a dog. J Small Anim Pract 52(4):220-223
  5. Kim MS et al (2010) Penile extramedullary plasmacytoma in a dog. Reprod Domest Anim 45(6):e454-e457
  6. Rannou B et al (2009) Rectal plasmacytoma with intracellular hemosiderin in a dog. Vet Pathol 46(6):1181-1184
  7. Van Wettere AJ et al (2009) Solitary intracerebral plasmacytoma in a dog: microscopic, immunohistochemical, and molecular features. Vet Pathol 46(5):949-951
  8. Tappin SW et al (2011) Serum protein electrophoresis in 147 dogs. Vet Rec 168(17):456
  9. Yearley JH et al (2007) Phagocytic plasmacytoma in a dog. Vet Clin Pathol 36(3):293-296
  10. Kato H et al (1995) Gammopathy with two M-components in a dog with IgA-type multiple myeloma. Vet Immunol Immunopathol 49(1-2):161-168
  11. Maczuzak, M et al (2003) Canine multiple myeloma
  12. Beethan R (2000) Detection of Bence-Jones protein in practice. Ann Clin Biochem 37:563-570
  13. MacEwen EG, et al (1984) Nonsecretory multiple myeloma in two dogs. J Am Vet Med Assoc 184:1283-1286
  14. Geigy C et al (2013) Multiple myeloma in a dog with multiple concurrent infectious diseases and persistent polyclonal gammopathy. Vet Clin Pathol 42(1):47-54
  15. Tizard IR (1996) B Cells and Their Response to Antigen. Veterinary Immunology, An Introduction, 5th ed. Philadelphia, W.B. Saunders Co., pp:121-140
  16. Vail DM (2000) Chapter 98- Hematopoietic Tumors. In: Ettinger SJ, Feldman EC (eds): Textbook of Veterinary Internal Medicine. Diseases of the Dog and Cat, 5th ed. Philadelphia, W.B. Saunders Co., pp:516-520
  17. Duncan JR, Prasse KW, Mahaffey EA (1994) Veterinary Laboratory Medicine. Clinical Pathology, 3rd ed. Ames, Iowa State University Press, pp:68-69
  18. Weber NA, CS Tebeau (1998) An unusual presentation of multiple myeloma in two cats. J Am Animal Hosp Assoc 34:477-483
  19. Doster DR, Folds J, Gabriel DA (1988) Nonsecretory multiple myeloma. Arch Pathol Lab Med 112:147-150
  20. Ramos-Vara JA et al (1998) Intestinal extramedullary plasmacytoma associated with amyloid deposition in three dogs: an ultrastructural and immunoelectron microscopic study. Ultrastruct Pathol 22(5):393-400
  21. Brunnert SR et al (1992) Gastric extramedullary plasmacytoma in a dog. J Am Vet Med Assoc 200(10):1501-1502
  22. Rusbridge C et al (1999) Vertebral plasma cell tumors in 8 dogs. J Vet Intern Med 13(2):126-313
  23. Matus RE et al (1983) Plasmapheresis and chemotherapy of hyperviscosity syndrome associated with monoclonal gammopathy in the dog. J Am Vet Med Assoc 183(2):215-218