Chapter 91: Thrombocytopenia

BACKGROUND

Thrombocytopenia, usually defined as an absolute platelet count less than 150,000/mm³, is a common cause of bleeding in pediatric patients. A low platelet count can be the result of increased platelet destruction, reduced production, consumption, or sequestration (Table 91-1), and considering these distinctions will help in formulating a differential diagnosis. Formation of a platelet plug is vital to hemostasis. Regardless of the cause, when platelet numbers are decreased, there can be petechiae, bruising, or bleeding. The body has a remarkable capacity to maintain hemostasis despite low platelet numbers, so symptoms may not become evident until the platelet count is quite low—usually below 50,000/mm³. Patients with moderately decreased platelet counts may be asymptomatic, with the thrombocytopenia being noted incidentally. This chapter focuses on the major causes of thrombocytopenia and their evaluation and management.

IMMUNE-MEDIATED THROMBOCYTOPENIA

THROMBOCYTOPENIC PURPURA

Clinical Presentation

The annual incidence of immune or idiopathic thrombocytopenic purpura (ITP) in children is about 50 per million, and it most commonly affects children between 2 and 6 years of age. The clinical definition of ITP was recently standardized to include peripheral blood platelet count less than 100 × 10⁹/L in the absence of other conditions associated with thrombocytopenia.¹ Immune thrombocytopenia is an autoimmune condition caused by antiplatelet antibodies, which leads to a drastically shortened platelet survival time due to platelet opsonization and enhanced clearance.² Primary ITP is the most common form (“typical ITP”), whereas secondary ITP can be ascribed to a secondary condition, such as administration of a live vaccine, viral infection, systemic lupus erythematosus, or human immunodeficiency virus.² A common presentation of primary ITP is an otherwise healthy child with the sudden onset of petechiae or bruising, or both, often with an antecedent febrile illness. As a general rule, thrombocytopenia is profound and typically the only abnormal finding in the complete blood count (CBC).

Differential Diagnosis

Since the age distribution and presenting symptoms of ITP can be very similar to that of acute leukemia, there is often some anxiety around the diagnostic workup for acute thrombocytopenia. In most cases, the history, physical examination, and review of the ...