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Myeloproliferative disorders (MPDs) are a closely related group of hematological malignancies in which the bone marrow cells that produce the body's blood cells develop and function abnormally. The disorders are progressive blood cancers that can strike anyone at any age, and for which there is no known cure. The three main myeloproliferative disorders are Polycythemia Vera (PV), Essential Thrombocythemia (ET) and Primary Myelofibrosis (PMF).
Polycythemia Vera is a clonal chronic progressive myeloproliferative disorder characterized by an absolute increase in the red cell mass and usually by an elevated leukocyte count, an elevated platelet count and an enlarged spleen. Polycythemia Vera differs from many other hematological malignancies in that prolonged survival is enjoyed by most patients if excessive production of red blood cells and platelets can be controlled. Clinical effects can be characterized by episodes of thromboses, bleeding and excessive itching after exposure to water. Prolonged survival can be interrupted by the development of other syndromes including myelofibrosis and acute leukemia. The most common causes of morbidity and mortality is the predisposition of polycythemia vera patients to develop life threatening arterial (heart attacks, strokes, intestinal gangrene) and venous (thromboses of the portal and /or hepatic veins, pulmonary embolism) thromboses. Treatment to return hematocrit to normal values is associated with a reduction of the number of thrombotic events.
Primary or Essential Thrombocythemia (ET)
Primary or Essential Thrombocythemia is a chronic myeloproliferative disorder characterized by a sustained proliferation of megakaryocytes which leads to an increased number of circulating platelets in excess of 600,000/mm3. This disorder is characterized by profound marrow megakaryocyte hyperplasia, splenomegaly and a clinical course punctuated by hemorrphagic or thrombotic episodes or both. Primary thrombocythemia is a clinically heterogeneous disorder with up to two-thirds of patients being asymptomatic at presentation. Most patients present with symptoms related to small or large vessel thrombosis or minor bleeding. Clots in the small arteries of the toes and fingers are common leading to digital pain enhanced by warmth, distal gangrene and classic erythromelalgia. The incidence of thrombotic and bleeding episodes is minimized but not eliminated with reduction of the platelet count to normal. Relatively rarely, primary thrombocythemia may evolve into acute leukemia or myelofibrosis.
Primary Myelofibrosis with Myeloid Metaplasia (MMF) is a chronic malignant hematological disorder characterized by an enlarged spleen, varying degrees of anemia and low platelet counts, red cells in the peripheral blood that resemble tear drops, the appearance of small numbers of immature nucleated red cells and white cells in the blood, varying degrees of fibrosis of the marrow cavity (myelofibrosis) and the presence of marrow cells outside the marrow cavity (extramedulary hematopoieses or myeloid metaplasia). MMF and marrow fibrosis are thought to be a response to a malignant proliferation of hematopoietic stem cells. The syndrome ultimately leads to marrow failure characterized by severe anemia and frequently low platelet counts. Nonspecific symptoms include fatigue, weight loss and night sweats. Symptoms due to an enlarging spleen are also common as the disease progresses. Optimal care is at present supportive and palliative but new strategies including stem cell transplantation show promise.
By Dr. Ron Hoffman
Professor, Medicine / Hematology and Medical Oncology, Mt. Sinai School of Medicine
More information about symptoms and treatments for the diseases can be found in the MPD Resources section.
