What is Immune Thrombocytopenic Purpura (ITP)?

What is ITP (Immune Thrombocytopenic Purpura)?

ITP is an autoimmune disorder where the immune system produces antibodies and cytotoxic T cells against platelet surface proteins, causing both accelerated platelet destruction and impaired platelet production, resulting in isolated thrombocytopenia (platelet count <150 × 10⁹/L) without other identifiable causes. 1, 2

Core Pathophysiology

ITP involves a dual mechanism that challenges the historical view of purely destructive disease:

• Increased platelet destruction: Autoantibodies coat platelets, leading to their removal by the reticuloendothelial system (spleen, liver) 1, 3
• Impaired platelet production: Autoantibodies also target megakaryocytes in the bone marrow, reducing new platelet formation 1, 2
• Immune dysregulation: Both humoral (antibody-mediated) and cell-mediated (cytotoxic T cells) immune responses contribute to the pathology 2, 4

Classification Systems

By Etiology:

• Primary ITP: Occurs in isolation without identifiable trigger or underlying condition 1, 2
• Secondary ITP: Associated with autoimmune diseases (antiphospholipid syndrome), viral infections (hepatitis C, HIV), or drugs (quinidine, heparin) 2

By Duration:

• Newly diagnosed: Initial presentation 1
• Persistent: 3-12 months duration 1
• Chronic: ≥12 months duration 1

Epidemiology and Natural History

• Incidence: 2-5 cases per 100,000 population annually 1
• Age-related remission rates in children: 74% in infants <1 year, 67% in ages 1-6 years, 62% in ages 10-20 years 1
• Adult prognosis: More likely to become chronic with lower spontaneous remission rates compared to children 1
• Mortality: Adults with ITP have 1.3-2.2-fold higher mortality than general population due to cardiovascular disease, infection, and bleeding 1

Clinical Presentation

Common Manifestations:

• Cutaneous bleeding: Bruising (ecchymoses) and petechiae are most frequent 1
• Mucosal bleeding: Gastrointestinal hemorrhage, hematuria, epistaxis, gingival bleeding 1

Severe Complications:

• Intracranial hemorrhage: Rare but life-threatening, occurring in 1.4% of adults and 0.1-0.4% of children 1
• Severe bleeding events: Reported in 9.5% of adults and 20.2% of children 1

Critical caveat: Many patients remain minimally symptomatic despite low platelet counts, while bleeding risk does not correlate perfectly with platelet count alone 1

Diagnostic Approach

ITP is a diagnosis of exclusion requiring three key features 1:

1. Isolated thrombocytopenia: Platelet count <150 × 10⁹/L (typically much lower at presentation)
2. Normal peripheral blood smear: Except for reduced platelet numbers
3. Absence of other causes: Must exclude drug-induced thrombocytopenia, viral infections, other autoimmune diseases, malignancy

When Bone Marrow Examination is Unnecessary:

• Children and adolescents with typical ITP features 1
• Patients who fail IVIg therapy 1
• Prior to corticosteroid treatment or splenectomy 1

Essential Medication History:

A thorough drug history is critical, as discontinuing an offending agent may resolve thrombocytopenia without immunosuppressive therapy 2

Severity Classification

• Mild (50-150 × 10⁹/L): Typically asymptomatic 5
• Moderate (20-50 × 10⁹/L): May develop cutaneous bleeding 5
• Severe (<20 × 10⁹/L): Significant risk of serious bleeding complications 5

Paradoxical Thrombotic Risk

Important consideration: Despite low platelet counts, ITP patients may have increased thrombotic risk due to young hyperactive platelets, platelet microparticles, complement activation, endothelial activation, and antiphospholipid antibodies 4

Activity Restrictions

Patients with platelet counts <50 × 10⁹/L should avoid contact sports and activities that increase trauma risk to prevent bleeding complications 5