What are the causes of immune thrombocytopenic purpura (ITP)?

Causes of Immune Thrombocytopenic Purpura

ITP is an autoimmune disorder caused by immunologic destruction of otherwise normal platelets, most commonly occurring in response to an unknown stimulus, with both increased platelet destruction and impaired platelet production contributing to the low platelet count. 1

Primary vs. Secondary ITP

Primary ITP

• Primary ITP occurs as an isolated condition without any identifiable underlying cause or associated disorder 1
• The autoimmune process targets platelet surface proteins with autoantibodies, leading to accelerated destruction in the reticuloendothelial system 2, 3
• Historically attributed solely to increased platelet destruction, newer evidence demonstrates that impaired platelet production by the bone marrow also plays a significant role in the pathophysiology 1

Secondary ITP

Secondary ITP occurs in association with identifiable underlying conditions, including: 1

Autoimmune Diseases

• Antiphospholipid antibody syndrome (particularly common) 1
• Systemic lupus erythematosus (SLE) - patients with SLE-associated ITP typically have higher median platelet counts and less bleeding compared to primary ITP 2
• Other collagen vascular disorders 3

Viral Infections

• Hepatitis C virus (HCV) - a well-characterized cause of chronic ITP 1, 4
• Human immunodeficiency virus (HIV) - affects 6-15% of infected patients 1, 4
• Cytomegalovirus (CMV) - increasingly recognized as causing severe, refractory ITP even in immunocompetent adults 5, 6
• Other viral illnesses may trigger ITP, particularly in children 3

Drug-Induced

• Certain medications can trigger immune-mediated thrombocytopenia 1

Lymphoproliferative Disorders

• Chronic lymphocytic leukemia (CLL) 7
• Hodgkin's disease and non-Hodgkin's lymphomas 7

Immune Deficiencies

• Primary immunodeficiency disorders can manifest with ITP 1, 3

Pathophysiologic Mechanisms

The dual mechanism involves: 1

• Accelerated platelet destruction via autoantibodies against platelet surface proteins, with clearance primarily in the spleen and reticuloendothelial system
• Impaired platelet production by megakaryocytes in the bone marrow, challenging the historical model that assumed only increased destruction

Clinical Pitfalls

Important caveat: When evaluating thrombocytopenia in patients with known autoimmune disease (especially SLE), other causes must be excluded before attributing it to ITP, including drug-induced thrombocytopenia, antiphospholipid syndrome, and thrombotic microangiopathic processes 2

Screening recommendations: The 2011 ASH guidelines recommend testing for HIV and Hepatitis C as part of the initial diagnostic workup 1. However, emerging evidence suggests that CMV testing should be considered in severe or refractory ITP cases, particularly before invasive procedures like splenectomy, even in asymptomatic patients 5, 6