Platelet Disorders

52 Platelet Disorders



Platelets are small anucleate cell particles (5-7 µL in volume) that play a critical role in primary hemostasis. At the time of vascular injury, platelets rush to the site of vascular damage and adhere to the exposed collagen, forming a temporary platelet plug to prevent continued bleeding. The platelets are then activated and undergo changes in their shape and structure. These changes allow the platelets to bind to fibrinogen and aggregate with one another, thus propagating the platelet plug. Activation of platelets also causes secretion of the chemicals contained in the platelet storage granules. These chemicals recruit new platelets and contain many compounds needed to continue primary hemostasis and activate secondary hemostasis (Figure 52-1).



Platelets are made in the bone marrow via fragmentation of megakaryocytes. Formation of platelets is controlled by thrombopoietin (TPO), which is a compound that controls megakaryocyte growth and maturation. Platelets typically circulate for 7 to 10 days and are then removed by the reticuloendothelial system. A normal platelet count is 150,000 to 400,000/µL. Platelet disorders can involve a qualitative or quantitative defect, and they are either inherited or acquired.



Etiology and Pathogenesis



Congenital Platelet Disorders


Congenital platelet disorders are individually very rare in the general population. They can have quantitative or qualitative abnormalities, and some disorders have both. Their mode of inheritance and their clinical significance vary. In general, children with congenital platelet disorders are more likely to have chronic bleeding symptoms that developed early in life. The following is a discussion of some of the important inherited platelet disorders.











Acquired Platelet Disorders


Acquired platelet disorders are far more common than congenital platelet disorders. The most common reason for acquired thrombocytopenia or an acquired platelet abnormality is drug exposure. Dozens of medications can cause thrombocytopenia or abnormalities in platelet function. These medications can act by inhibiting bone marrow production of platelets or activating or creating antibodies to platelets, or they can have a direct toxic effect on platelets. Refer to Table 52-1 for a list of some of the common medications resulting in thrombocytopenia and platelet function abnormalities. Heparin-induced thrombocytopenia (HIT) is a special case and is discussed again later this chapter.


Table 52-1 Common Medications Resulting in Thrombocytopenia or Platelet Function Abnormalities








Drugs Associated with Thrombocytopenia Drugs Associated with Abnormal Platelet Function

Stay updated, free articles. Join our Telegram channel

Jun 19, 2016 | Posted by in PEDIATRICS | Comments Off on Platelet Disorders

Full access? Get Clinical Tree

Get Clinical Tree app for offline access