Lymphoproliferative and myeloproliferative disorders

LYMPHOPROLIFERATIVE AND MYELOPROLIFERATIVE DISORDERS

LYMPHOPROLIFERATIVE DISORDERS

  • Restricted to disorders of lymphocytic (e.g., lymphoma, acute lymphoblastic leukemia, reticulum cell sarcoma, Hodgkin's) or plasma cell (e.g., multiple myeloma) origin.

MYELOPROLIFERATIVE DISORDERS

  • A myeloproliferative disorder is a primary bone marrow disease of unknown etiology and encompasses disorders of hematopoietic stem cells as well as of granulocytic, monocytic, erythrocytic and megakaryocytic series.
  • The disease may involve any one or a combination of two or more of the different cell lines comprising the cytology of bone marrow. The schematic outline of the myelo-proliferative disease complex is indicated on the following page.
  • The clinical signs and symptoms might include the following:
    • Chronic progressive weight loss.
    • Emaciation, anorexia and depression.
    • Severe and progressive nonregenerative anemia.
    • Spleen and liver may be enlarged.

Features of myeloproliferative disease include:

  • Phagocytosis of nucleated and mature RBC by macrophages within the bone marrow.
  • Usually get involvement of the bone marrow, spleen, liver and lymph nodes.
  • Icterus may be present when there is aggressive erythrophagocytosis by the reticuloendothelial system (RE system).
  • Some cases of myeloproliferative disease may terminate in myelofibrosis.
  • A C-type leukemia virus has been demonstrated in the bone marrow of some cats with this disease.
  • A striking feature of the myeloproliferative disease is the tendency to undergo transition from one cell type to another during the course of the clinical disease.

CANINE LEUKEMIA COMPLEX

Lymphoproliferative Disorders

a.CANINE LYMPHOSARCOMA

  • Lymphosarcoma is the most frequent tumor found in the dog. It occurs primarily in dogs 5 years of age and over. Characteristic features of the tumor include:
  • Bilateral painless swelling of superficial lymph nodes.
  • Usually there is no fever.
  • Anemia may be present but usually not severe
  • Two clinical forms can be identified:
  • MULTICENTRIC FORM
    • Is characterized by enlarged superficial lymph nodes, enlarged spleen and liver. Might see involvement of almost any organ in the body.
  • ALIMENTARY FORM
    • Involves the alimentary tract and mesenteric lymph nodes but rarely involves superficial lymph nodes or the spleen.
  • The total leukocyte count and the differential count may reveal a leukocytosis with a left shift and a modest monocytosis. Only about 20% of the dogs will show a lymphocytosis and 25% will show a frank lymphopenia. Approximately 53% of the dogs showed some degree of thrombocytopenia.
  • It is generally agreed that the peripheral blood examination is not diagnostic for canine lymphosarcoma. Neoplastic cells may appear irregularly in small numbers.
  • Careful examination of the peripheral blood and the finding of lymphoblast and prolymphocytes might be more informative than the total leukocyte count. Lymph node impression smears and films from aspirated fluid from lymph nodes should be used in conjunction with the peripheral blood in making a diagnosis.
  • Bone marrow is not regularly invaded in lymphosarcoma. A few cases have been reported with total leukocyte count in excess of 100,000.
  • Boxers and Scottish Terriers appear more susceptible and Dachshunds less susceptible to lymphosarcoma.

b.BURKITT'S LYMPHOMA AND CANINE LYMPHOSARCOMA

This is a non-leukemic lymphoid tumor involving the visceral organs and bone marrow, particularly of the jaw.

A characteristic feature is the scattering of phagocytic histiocytes among densely packed neoplastic lymphocytes, a pattern that gave rise to the descriptive "starry sky" effect". A large number of canine lymphomas also present the "starry sky" pattern indicating a possible related etiologic agent.

c.HODGKIN's DISEASE

This disease consists of a granulomatous process in the lymph nodes that begins with lymphocytic hyperplasia followed by a gradual loss of normal architecture with replacement of the lymphocytes as the disease progresses.

Typical Hodgkin's disease has not been shown to occur in animals except one instance of canine malignant lymphoma simulating the disease. Multinuclear giant cells called "Reed-Sternberg cells"are Pathognomonic for the disease and their presence is essential for a diagnosis.

d.PLASMA CELL MYELOMA

This neoplasm arises in the bone marrow from plasma cells. Multiple foci throughout the skeleton have led to the designation "multiple myeloma."

Pain, lameness, and sometimes fracture of weakened bones are common clinical signs. Neoplastic plasma cells commonly invade the liver, spleen, kidneys, and lymph nodes.

The myeloma plasma cell synthesizes protein, so hyperproteinemia is to be anticipated. The hyperglobulinemia may be associated with Bence Jones Protein in the urine. Multiple myeloma is not a common disease of animals.

Myeloproliferative Disorders

a.GRANULOCYTIC (MYELOGENOUS) LEUKEMIA

This type of leukemia occurs primarily in young dogs. A truly leukemic blood picture has been a common finding in granulocytic leukemia in the dog.

In the event the neoplastic cells are too primitive or bizarre to be classified as granulocytes, their granulocytic origin can be verified by a positive peroxidase stain.

A positive reaction for alkaline phosphatase is viewed as evidence that the cells are leukemic granulocytes since normal granulocytes are alkaline phosphatase negative.

1)CLINICAL SIGNS

  • Progressive weakness
  • Weigh loss over a period of several months
  • Moderate lymphadenopathy of peripheral lymph nodes
  • Splenomegaly and sometimes hepatomegaly

2)TYPICAL BLOOD PICTURE

  • Neutrophilia with a left shift to the myeloblast stage.
  • May also see hypersegmentation of mature-like neutrophils
  • Neoplastic neutrophils are susceptible to rapidly degenerative changes which consist of vacuolation of the cytoplasm
  • Difficult to differentiate degenerating neoplastic neutrophils from monocytes.
  • Severe anemia is a common feature
  • Thrombocytopenia may also be seen

b. MAST CELL LEUKEMIA

  • Mast cell tumors are of common occurrence in dogs but mast cell leukemia is rarely seen. The total leukocyte count is usually normal but the differential contains numerous mast cells in the peripheral blood and bone marrow.
  • Tissue section stained by Giemsa method revealed metachromatic cytoplasmic granules in the neoplastic cells. Ulceration in the GI tract may occur due to histamine release from the mast cells.
Last modified: Tuesday, 5 June 2012, 1:31 PM