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the change in the type of adult cells in a tissue to a form abnormal for that tissue. adj., adj metaplas´tic.
agnogenic myeloid metaplasia the primary or idiopathic form of myeloid metaplasia, which is often accompanied by myelofibrosis; it is considered one of the myeloproliferative disorders. Called also aleukemic or nonleukemic myelosis.
myeloid metaplasia the occurrence of myeloid tissue in extramedullary sites; specifically, a syndrome characterized by splenomegaly, anemia, nucleated erythrocytes and immature granulocytes in the circulating blood, and extramedullary hematopoiesis in the liver and spleen. The primary form is called agnogenic myeloid metaplasia. The secondary or symptomatic form may be associated with various diseases, including carcinomatosis, tuberculosis, leukemia, and polycythemia vera.
a syndrome characterized by anemia, enlargement of the spleen, nucleated red blood cells and immature granulocytes in the circulating blood, and conspicuous foci of extramedullary hemopoiesis in the spleen and liver; may develop in the course of polycythemia rubra vera; there is a high incidence of development of myeloid leukemia.
chronic idiopathic myelofibrosisA chronic progressive condition characterised by panmyelosis and variable marrow fibrosis, massive splenomegaly secondary to extramedullary haematopoiesis, and leukoerythroblastic anaemia with dysmorphic red blood cells, circulating normoblasts, immature white blood cells and atypical platelets.
Patients are often > age 50, suffer from insidious weight loss, anaemia, and abdominal discomfort due to splenomegaly, often with hepatomegaly; 80% have nonspecific chromosome defects.
Bone marrow biopsy.
No specific therapy; packed RBCs for anaemia; androgens may reduce transfusion requirements, but are poorly tolerated in women; recombinant erythropoietin.
Survival ± 5 years, often progresses to acute leukaemia.
No name used for this condition has proven consistently satisfactory to those who work in the field. Chronic idiopathic myelofibrosis is preferred by the World Health Organisation, while others prefer the term primary myelofibrosis. None of the terms fully take into account the functional defects—e.g., haemopoietic stem cell disturbance, extramedullary haemopoiesis and the pathological changes seen in the bone marrow (e.g., intense marrow fibrosis).
my·e·loid met·a·pla·si·a(mī'ĕ-loyd met'ă-plā'zē-ă)
A syndrome characterized by anemia, enlargement of the spleen, nucleated red blood cells and immature granulocytes in the blood, and foci of extramedullary hemopoiesis in the spleen and liver; may develop in the course of polycythemia rubra vera; there is a high incidence of development of myeloid leukemia.