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CMDT 2013
14
Disorders of Hemostasis, Thrombosis, & Antithrombotic Therapy Patrick F. Fogarty, MD Tracy Minichiello, MD
In assessing patients for defects of hemostasis, the clinical context must be considered carefully (Table 14–1). Heritable defects are suggested by bleeding that begins in infancy or childhood, is recurrent, and occurs at multiple anatomic sites, although many other patterns of presentation are possible. Acquired disorders of hemostasis more typically are associated with bleeding that begins later in life and may be relatable to introduction of medications (eg, agents that affect platelet activity) or to onset of underlying medical conditions (such as renal failure or myelodysplasia), or may be idiopathic. Importantly, however, a sufficient hemostatic challenge (such as major trauma) may produce excessive bleeding even in individuals with completely normal hemostasis. Fogarty PF et al. Disorders of Hemostasis I: Coagulation. In: Rodgers GP et al (editors). The Bethesda Handbook of Clinical Hematology. Philadelphia: Lippincott Williams and Wilkins, 2010.
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PLATELET DISORDERS
Thrombocytopenia The causes of thrombocytopenia are shown in Table 14–2. The age of the patient and presence of any comorbid conditions may help direct the diagnostic work-up. The risk of spontaneous bleeding (including petechial hemorrhage and bruising) does not typically increase appreciably until the platelet count falls below 10,000– 20,000/mcL, although patients with dysfunctional platelets may bleed with higher platelet counts. Suggested platelet counts to prevent spontaneous bleeding or to provide adequate hemostasis around the time of invasive procedures are found in Table 14–3.
Decreased Platelet Production 1. Bone Marrow Failure
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Essentials of diagnosis
Bone marrow failure states may be congenital or acquired. `` Most congenital marrow failure disorders present in childhood. ``
``General Considerations Congenital conditions that cause thrombocytopenia include amegakaryocytic thrombocytopenia, the thrombocytopeniaabsent radius (TAR) syndrome, and Wiskott-Aldrich syndrome; these disorders usually feature isolated thrombocytopenia, whereas patients with Fanconi anemia and dyskeratosis congenita typically have depressions in other blood cell counts as well. Acquired causes of bone marrow failure leading to thrombocytopenia include acquired aplastic anemia, myelodysplastic syndrome (MDS), and acquired amegakaryocytic thrombocytopenia. Unlike aplastic anemia, MDS is more common among older patients.
``Clinical Findings Acquired aplastic anemia typically presents with reductions in multiple blood cell lines; a bone marrow biopsy subsequently reveals hypocellularity. Myelodysplasia may also present as cytopenias with variable marrow cellularity, at times mimicking aplastic anemia; however, the presence of macrocytosis, ringed sideroblasts on iron staining of the bone marrow aspirate, dysplasia of hematopoietic