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Basics ⬇

Outline

BASICS

Overview!!navigator!!

  • Rare neoplasm caused by the malignant proliferation of plasma cells
  • Primarily arises from the bone marrow, but can originate from, or metastasize to, extramedullary organs

Signalment!!navigator!!

  • Quarter Horses are overrepresented
  • Age range—3 months to 25 years

Signs!!navigator!!

  • Nonspecific signs; weight loss, peripheral edema, fever, and lymphadenopathy
  • Other signs include anorexia, pneumonia, rear leg paresis/ataxia, epistaxis, bone pain, and soft feces

Causes and Risk Factors!!navigator!!

None identified.

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

  • Diagnosis made if combination of 1 major and 1 minor criteria or 3 minor criteria are found
  • Major criteria—bone marrow plasmacytosis >30%; biopsy diagnosis of a plasmacytoma with evidence of uncontrolled production of a monoclonal immunoglobulin or protein fragment (paraprotein or M-component)
  • Minor criteria—bone marrow plasmacytosis <30%, serum or urine paraprotein present in lower concentrations; 50% decrease in other immunoglobulin classes; and osteolytic bone lesion(s)

Differential Diagnosis!!navigator!!

  • Lymphoma and lymphoid leukemia; differentiated by identification of neoplastic lymphocytic proliferation on tissue/bone marrow biopsy
  • Single plasmacytoma; differentiated by lack of paraneoplastic syndromes, monoclonal gammopathy, or diffuse bone marrow involvement
  • Other causes of monoclonal gammopathy, e.g. chronic bacterial or fungal infection; differentiated by response to treatment and diagnostic serology identifying causative agent
  • Benign monoclonal gammopathy; diagnosis of exclusion

CBC/Biochemistry/Urinalysis!!navigator!!

  • Hyperproteinemia with hyperglobulinemia and hypoalbuminemia
  • Hyperviscosity of serum
  • Myelophthisic disease; anemia, thrombocytopenia, leukopenia
  • Plasma cell leukemia
  • Hypercalcemia due to PTHrP or renal failure
  • Renal failure with proteinuria and azotemia
  • Hyponatremia

Other Laboratory Tests!!navigator!!

  • Serum/urine electrophoresis indicative of a monoclonal gammopathy
  • Bence Jones proteinuria
  • Elevated PTHrP

Imaging!!navigator!!

  • Radiography; focal, punctate bone lysis, periosteal reaction and sclerosis, diffuse osteoporosis, or pathologic fractures
  • Ultrasonography; masses in the abdominal or thoracic cavities

Other Diagnostic Procedures!!navigator!!

  • Bone marrow aspirate/biopsy; identification of plasmacytosis (>10%) and atypical plasma cells with nuclear–cytoplasmic asynchrony
  • Repeat bone marrow aspirates at several sites if bone involvement is focal
  • Biopsy of extraosseous tissues such as spleen, liver, lymph nodes, and kidney may reveal infiltration of neoplastic plasmacytoid cells
  • Immunofluorescence/histochemical labeling of cytoplasmic or surface immunoglobulins can identify monoclonal plasma cell populations suggestive of malignant plasmacytosis

Pathologic Findings!!navigator!!

  • Neoplastic plasma cell infiltration (>10%) of bone marrow
  • Focal or diffuse bone lesions including osteoporosis, cortical erosion, pathologic fractures, and grossly visible tumor with normal to increased number of plasma cells or atypical plasma cells
  • Plasma cell infiltration of tissues, particularly spleen, liver, lymph nodes, and kidney
  • Immunoglobulin or amyloid deposition in the kidneys

Treatment ⬆ ⬇

TREATMENT

Inpatient care to provide supportive treatment to relieve associated clinical problems and side effects of chemotherapeutic agents.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Short-term stabilization of disease (7–12 months) reported in horses treated with melphalan; cyclophosphamide and prednisolone also given to these horses; dose rates not reported
  • Doxorubicin (70 mg/m2 IV every 2 weeks) may result in clinical improvement
  • Corticosteroid therapy (prednisolone 1 mg/kg PO every 24 h or dexamethasone 0.1 mg/kg every 24 h) may provide palliative relief

Contraindications/Possible Interactions!!navigator!!

  • Cyclophosphamide—bone marrow suppression and hemorrhagic cystitis
  • Doxorubicin—bone marrow suppression, hyperthermia, colic
  • Corticosteroids—laminitis, iatrogenic Cushing syndrome

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • Progressive pancytopenia due to myelophthisis
  • Serial monitoring of PTHrP and globulin concentrations in horses with unconfirmed multiple myeloma may be useful

Prevention/Avoidance!!navigator!!

N/A

Possible Complications!!navigator!!

Acquired secondary infections, particularly pneumonia, due to impaired immunologic function.

Expected Course and Prognosis!!navigator!!

Median life expectancy after diagnosis is 3 months; range 1.5 months to 2 years.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • Systemic light-chain amyloidosis (1 case)
  • Idiopathic multifocal smooth muscle hypertrophy (1 case)

Age-Related Factors!!navigator!!

N/A

Zoonotic Potential!!navigator!!

None

Pregnancy/Fertility/Breeding!!navigator!!

Most chemotherapeutic agents have embryo lethal and teratogenic effects.

Abbreviations!!navigator!!

PTHrP = parathyroid hormone-related protein

Suggested Reading ⬆ ⬇

Munoz A, Riber C, Trigo P, Castejon F. Hematopoietic neoplasias in horses: myeloproliferative and lymphoproliferative disorders. J Equine Sci 2009;20:59–72.

Author(s) ⬆

Author: Krista Estell

Consulting Editors: David Hodgson, Harold C. McKenzie, and Jennifer L. Hodgson

Acknowledgment: The author and editors acknowledge the prior contribution of Rachel Tan.