1 What are chronic myeloproliferative disorders?

Chronic myeloproliferative disorders (CMPDs) are clonal bone marrow disorders that result in the production of excessive numbers of mature, morphologically unremarkable, hematopoietic cells of the myeloid lineage (erythrocytes, granulocytes, and platelets). These neoplastic conditions arise from the proliferation of an abnormal hematopoietic stem cell that retains its ability to differentiate and mature. Although the term encompasses a variety of diseases and each disorder is unique, there is considerable overlap of clinical and laboratory features among the CMPDs. In contrast to acute leukemias, CMPDs tend to have a protracted clinical course.

2 Identify the diseases classified as CMPDs and the primary cell line affected.

The CMPDs are classified primarily based on the hematopoietic cell line that predominates. However, it is important to recognize that all the myeloid lineages (granulocytic, megakaryocytic, erythroid) may be involved in each of the diseases. In addition, the presence or absence of marrow fibrosis is an important diagnostic criterion for classification of CMPDs. Table 15-1 lists the CMPDs and the predominant hematopoietic cell lines affected.

Table 15-1 Classification of Chronic Myeloproliferative Disorders

* Recognized as CMPDs by the World Health Organization classification system.

Note: Traditionally this category encompassed the following four disorders: polycythemia vera, essential thrombocythemia, idiopathic myelofibrosis, and chronic myelogenous leukemia.

3 What clinical or laboratory features do the CMPDs have in common?

The similarities among the CMPDs are the result of a marked proliferation of leukemic cells. Table 15-2 lists common features of CMPDs provided by physical examination, peripheral blood, and bone marrow findings.

Table 15-2 Common Features of Chronic Myeloproliferative Disorders

* Most often seen. However, bone marrow failure (ineffective hematopoiesis) may be observed in the late stages of CMPDs.

4 Can CMPDs transform into acute leukemias?

All the CMPDs have the potential to progress into acute myeloid leukemias. In veterinary medicine, little is known about the transformation rate of each disorder.

5 What tests are used to diagnose CMPDs?

The diagnosis of a CMPD is challenging. Critical diagnostic tests include complete blood count (CBC) and peripheral blood smear examination, bone marrow aspirate cytology, and bone marrow core biopsy with histopathology. In human medicine, genetic testing such as cytogenetics and molecular analyses are important criteria in the diagnostic workup. To diagnose a CMPD, it is essential to correlate the history and physical examination findings with the results of laboratory testing. Although diagnostic criteria exist for each disorder, a major component of the diagnostic workup is the exclusion of reactive processes.

6 What is polycythemia vera?

The term polycythemia or erythrocytosis is used to describe an abnormally elevated red blood cell (RBC) mass, as measured by hemoglobin or hematocrit. Polycythemia vera (PV) is a neoplastic hematopoietic stem cell disorder typified by excessive erythropoiesis. The neoplastic clone proliferates uncontrollably and independent of the mechanisms that regulate RBC production, resulting in increased numbers of mature RBCs in circulation. Although the erythroid cell line is predominantly affected, other hematopoietic cells of myeloid origin may also be involved. PV has been documented primarily in the dog and the cat.

7 List the major history and clinical findings associated with polycythemia vera.

The history and clinical findings in an animal with PV are related to the marked increase in RBC mass that accompanies this disease. The excessive proliferation of mature erythrocytes often increases blood viscosity, causing reduced blood flow within vessels and suboptimal delivery of oxygen to tissues (tissue hypoxia). Box 15-1 lists clinical findings associated with PV.

8 List the major peripheral blood and bone marrow findings associated with polycythemia vera.

Table 15-3 lists peripheral blood and bone marrow findings associated with PV.

Table 15-3 Peripheral Blood and Bone Marrow Findings Associated with Polycythemia Vera

* Not typical in animals (seen in humans with PV).

9 How is polycythemia vera diagnosed?

A diagnosis of PV requires documentation of an absolute increase in RBC mass and exclusion of other causes of polycythemia. To diagnose an absolute polycythemia, the possibility of a relative polycythemia should initially be eliminated. A relative increase in RBC mass may result from decreased plasma volume caused by dehydration. Splenic contraction (caused by catecholamine release) can also increase RBC mass by releasing mature erythrocytes into circulation, resulting in an increased RBC count. With both these situations (hemoconcentration or redistribution), the true or total body RBC mass is not increased; these are transient conditions.

Once an absolute polycythemia is confirmed, the elevation in RBC mass should be classified as primary or secondary based on erythropoietin production and concentration. Erythropoietin is a glycoprotein produced by the renal interstitial cells that stimulates erythrocyte production. With primary polycythemia (PV) the neoplastic cells proliferate independently of normal regulatory mechanisms (autonomous of erythropoietin levels), and animals with PV tend to have normal to low erythropoietin levels.

Secondary polycythemia arises from increased secretion of erythropoietin. This category can be further divided into appropriate or inappropriate with respect to tissue oxygenation. Increased serum erythropoietin levels and the resultant polycythemia are appropriate in situations when tissue hypoxia is present. Inappropriate increases in erythropoietin also occur, regardless of tissue oxygenation status (independent of tissue hypoxia). The increase in serum erythropoietin and RBC mass that occurs with inappropriate polycythemia is unwarranted and unnecessary.

Table 15-4 lists conditions associated with relative, primary, and secondary appropriate and inappropriate polycythemia.

Table 15-4 Conditions Associated with Polycythemia and Diagnostic Tests

TYPE	CAUSE	DIAGNOSTIC TESTS
Relative	Dehydration Only gold members can continue reading. Log In or Register to continue Share this: Click to share on Twitter (Opens in new window) Click to share on Facebook (Opens in new window) Related Related posts: ERYTHROCYTE DISORDERS MYELODYSPLASTIC SYNDROMES LABORATORY TESTING FOR THYROID DISEASE METABOLIC ACID-BASE ABNORMALITIES Stay updated, free articles. Join our Telegram channel Join Tags: Veterinary Clinical Pathology Secrets Aug 26, 2016 | Posted by admin in INTERNAL MEDICINE | Comments Off on CHRONIC MYELOPROLIFERATIVE DISORDERS Full access? Get Clinical Tree Get Clinical Tree app for offline access Get Clinical Tree app for offline access