Conditions that affect the bone marrow can also lead to thrombocytopenia. It may be necessary to examine bone marrow smears and sections to diagnose the primary condition causing the decrease in circulating platelets.
- In leukemia, the platelet count is diminished as a result of displacement in the bone marrow of normal hematopoietic cells (including megakaryocytes and their precursor cells) by leukemic cells. If megakaryocytes are reduced in the bone marrow, the number of circulating platelets will be reduced.
- Chemotherapy can lead to transient thrombocytopenia since it interferes with the cell cycle of normal as well as tumor cells.
- In patients with aplastic anemia, where the stem cells are not functioning properly, thrombocytopenia occurs as the bone marrow becomes more and more hypoproliferative.
- Pancytopenia is often seen with megaloblastic anemias caused by folic acid or vitamin B12 deficiency. Thrombopoiesis (as well as erythropoiesis and granulopoiesis) is ineffective. The bone marrow contains a normal or even increased number of megakaryocytes, but the number of platelets entering the peripheral circulation is decreased.
- Certain myelodyplasias can lead to one or more blood cell cytopenias, including thrombocytopenia.