1. IMMUNE THROMBOCYTOPENIA
ESSENTIALS OF DIAGNOSIS
Isolated thrombocytopenia (rule out pseudothrombocytopenia by review of peripheral smear).
Assess for any new causative medications and HIV, hepatitis B, and hepatitis C infections.
ITP is a diagnosis of exclusion.
ITP is an autoimmune condition in which pathogenic antibodies bind platelets, accelerating their clearance from the circulation. Many patients with ITP also lack appropriate compensatory platelet production, thought, at least in part, to reflect the antibody’s effect on megakaryocytopoiesis and thrombopoiesis. ITP is primary (idiopathic) in most adult patients, although it can be secondary, (ie, associated with connective tissue disease, such as systemic lupus erythematosus; lymphoproliferative disease, such as lymphoma; medications; and infections, such as hepatitis C virus and HIV infections). Antiplatelet antibody targets include glycoproteins IIb/IIIa and Ib/IX on the platelet membrane, although antibodies are demonstrable in only two-thirds of patients. In addition to production of antiplatelet antibodies, HIV and hepatitis C virus may lead to thrombocytopenia through additional mechanisms (for instance, by direct suppression of platelet production [HIV] and cirrhosis-related decreased TPO production and secondary splenomegaly [hepatitis C virus]).
Mucocutaneous bleeding may be present, depending on the platelet count. Clinically relevant spontaneous bruising, epistaxis, gingival bleeding, or other types of hemorrhage generally do not occur until the platelet count has fallen below 10,000–20,000/mcL. Individuals with secondary ITP (such as due to collagen vascular disease, HIV or HCV infection, or lymphoproliferative malignancy) may have additional disease-specific findings.
Typically, patients have isolated thrombocytopenia. If bleeding has occurred, anemia may also be present. Hepatitis B and C viruses and HIV infections should be excluded by serologic testing. Bone marrow should be examined in patients with unexplained cytopenias in two or more lineages, in patients older than 40 years with isolated thrombocytopenia, or in those who do not respond to primary ITP-specific therapy. A bone marrow biopsy is not necessary in all cases to make an ITP diagnosis in younger patients. Megakaryocyte morphologic abnormalities and hypocellularity or hypercellularity are not characteristic of ITP. ITP patients often have increased numbers of bone marrow megakaryocytes. If there are clinical findings suggestive of a lymphoproliferative malignancy, a CT scan should be performed. In the absence of such findings, otherwise asymptomatic patients younger than 40 years with unexplained isolated thrombocytopenia of recent onset may be considered to have ITP. Helicobacter pylori infections can sometimes cause isolated thrombocytopenia.
Individuals with platelet counts less than 25,000–30,000/mcL or those with significant bleeding should be treated; the remainder may be monitored serially for progression, but that is a patient-specific decision. The mainstay of initial treatment of new-onset primary ITP is a short course of corticosteroids with or without intravenous immunoglobulin (IVIG) or anti-D (WinRho) (Figure 14–1...