Acquired disorders of the bone marrow

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Bone marrow disorders may either be congenital or acquired. Only acquired bone disorders are discussed below. Bone marrow disorders may be myelosuppression, myeloproliferation, or mixed/unclassified (features of both).

Classification

Bone marrow disorders include:

• Myelosuppressive disorders: Reduced numbers of cells in bone marrow
• Myeloproliferative disorders: Increased numbers of cells in bone marrow
• Mixed or Unclassified: Contains features of both myeloproliferation and myelodysplasia

Myelosuppressive Disorders

Myelosuppressive disorders are characterized by either pancytopenia or selective lineage deficiency caused by deficient hematopoiesis at the level of the bone marrow. Bone marrow failure may be a result of a congenital disease or an acquired disease.

All Hematopoietic Lineages

• Myelodysplasia (aka Myelodysplastic syndrome): A cause of bone marrow failure characterized by defective stem cells that fail to undergo normal maturation. Bone marrow appears HYPER cellular in myelodysplasia.

• Aplastic anemia (aka Aplastic pancytopenia , bone marrow hypoplasia, hypoplastic bone marrow, bone marrow aplasia, aplastic bone marrow, ehrlich anemia): A cause of bone marrow failure that may be hereditary (Fanconi’s anemia) or acquired (drugs, chemicals, radiation, or viruses). It is a distinct disease characterized by an “empty” bone marrow. Pancytopenia is a manifestation of aplastic anemia. Unlike MDS, the bone marrow appears HYPOcellular in aplastic anemia. Aplastic anemia is not characterized by abnormal mature cells, and the few cells that mature are normal in aplastic anemia. Aplastic anemia is a misnomer since not only RBC (anemia) is affected.

• Paroxysmal nocturnal hemoglobinuria: Bone marrow failure characterized by clonal expansion of a mutated hematopoietic stem cell.

Selective hematopoietic lineages

• Pure red cell aplasia (aka erythroblastopenia): Insufficient production of RBC characterized by absence or deficient erythroblasts in the bone marrow

• Neutropenia( aka granulocytopenia, granulopenia, agranulocytosis, agranulosis, neutrophilic leukopenia, neutrophilic leukocytopenia, neutrophilic leucopenia, neutrophilic leucocytopenia): Neutropenia is defined absolute neutrophil count < 1.5 x 109/L. Agranulocytosis is defined as severe neutropenia < 0.5 x 109/L. Although agranulocytosis and granulocytopenia should include reduced numbers of all granulocytes (either neutrophils, eosinophils, or basophils), the majority of cases of granulocytopenia are actually neutropenia since neutrophils constitute the majority of leukocytes; the term granulocytopenia almost always refers to deficient neutrophils.

• Amegakaryocytic thrombocytopenia: Thrombocytopenia caused by a reduced number of megakaryocytes in the bone marrow