Thrombocytopenia pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1], Associate Editor-In-Chief: Farbod Zahedi Tajrishi
Overview
Pathophysiology
Physiology
Platelets are produced in hematopoiesis by budding off from megakaryocytes, which are produced by pluripotent hematopoietic stem cells.[1] Each megakaryocyte produces 1000 to 5000 platelets. Platelets circulate for approximately one week, and are then destroyed by the spleen and by Kuppfer cells in the liver.
Pathogenesis
It is thought that thrombocytopenia is the result of either of these four main mechanisms:
- decreased production of platelets in the bone marrow,
- destruction of platelets outside of bone marrow,
- blood dilution from fluid resuscitation or massive transfusion,
- sequestration of platelets in the spleen due to portal hypertension and/or splenomegaly.
Some conditions cause thrombocytopenia through a combination of these mechanisms. For instance, primary ITP is associated with antibody-mediated platelet destruction, but it can also cause suppression of megacaryocytes, which is considered a bone marrow dysfunction.
| main cause | mechanism and further explanations | examples |
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| Bone marrow dysfunction | Bone marrow abnormalities that cause decreased platelet production commonly reduce the production of RBCs and WBCs as well, resulting in pancytopenia. Common presentations include symptoms of thrombocytopenia (eg, bleeding, petechiae) or symptoms associated with anemia and/or leukopenia (eg, shortness of breath, fatigue and recurrent infections). | |
| Platelet destruction/consumption | Several mechanisms can accelerate the normal platelet degradation process in the body:
Anti-platelet antibodies seen in both primary ITP and its secondary form (associated with systemic autoimmune disorders such as SLE) play a main role. Antibody-mediated reactions can also cause a reduction in other blood cell lines, resulting in combined cytopenias. Some medications and ingested substances can also cause thrombocytopenia through this mechanism. |
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| Dilution | An additional mechanism of thrombocytopenia is dilutional thrombocytopenia, as occurs in the setting of massive fluid resuscitation or massive transfusion. Platelet counts are reduced in proportion to the number of RBC units transfused in a 24-hour period [10,11]. Ratios of platelets to other products are discussed separately |
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| Redistribution/splenomegaly | In individuals with normal splenic function, approximately one-third of the platelet mass is found in the spleen, in equilibrium with the circulating platelet pool [12]. Conditions that increase splenic size and/or cause splenic congestion through portal hypertension (eg, cirrhosis, alcoholic liver disease) can decrease the platelet count without altering the total platelet mass in the body (figure 1) [12]. Severe thrombocytopenia or bleeding in the setting of splenomegaly should prompt the clinician to investigate for other causes. |
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References
- ↑ Klein LS, Shih HT, Hackett FK, Zipes DP, Miles WM (1992). "Radiofrequency catheter ablation of ventricular tachycardia in patients without structural heart disease". Circulation. 85 (5): 1666–74. PMID 1572025.