Immune Thrombocytopenic Purpura (ITP)

Introduction And Epidemiology

• Previously designated idiopathic thrombocytopenic purpura; currently termed immune thrombocytopenic purpura (ITP) due to established autoimmune pathogenesis.
• Most common etiology of acute onset thrombocytopenia in otherwise-healthy children.
• Incidence ranges between 7.2-9.5 per 100,000 children.
• Peak incidence occurs between 1-7 years of age.
• Equal sex distribution observed in young children; higher prevalence noted in adolescent females.
• Seasonal clustering prominent during late winter and springtime.

Pathophysiology And Mechanisms

• Pathogenesis involves immune-mediated platelet destruction combined with impaired platelet production.
• Antibody-Mediated Destruction:
  • Autoantibodies target specific platelet surface glycoproteins, predominantly GPIIb/IIIa, GPIb/IX, and GPIa/IIa complexes.
  • Splenic macrophages recognize IgG Fc region of antiplatelet antibodies, leading to phagocytosis and destruction.
  • Antibodies against GPIb/IX may induce platelet desialylation, resulting in hepatic clearance via carbohydrate receptors.
• Impaired Megakaryopoiesis:
  • Relative decrease in megakaryocyte production contributes significantly to thrombocytopenia.
  • Cytotoxic T-cells and specific immune cytokines impair megakaryocyte function and platelet generation.
  • Thrombopoietin levels remain minimally elevated, failing to adequately compensate for destruction.
• Immunologic Dysregulation:
  • Disease characterized by Th1 dominant proinflammatory cytokine state.
  • Upregulation of genes mediating cellular toxicity (granzyme B, perforin) in CD3+/CD8+ T-cells.
  • CD4+ T-helper cells stimulate autoantibody-secreting B-cells.
• Triggering Events:
  • Acute viral infections frequently precede onset by 1-4 weeks.
  • Implicated agents include Epstein-Barr virus (EBV), human immunodeficiency virus (HIV), cytomegalovirus (CMV), varicella, rubella, hepatitis C, parvovirus, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
  • Associated with Helicobacter pylori infection and rarely follows measles, mumps, and rubella (MMR) vaccination.

Classification Based On Disease Duration

• Acute ITP: Thrombocytopenia resolving within 3 months.
• Persistent ITP: Thrombocytopenia lasting 3-12 months.
• Chronic ITP: Thrombocytopenia persisting beyond 12 months.

Clinical Manifestations And Bleeding Severity

• Patients typically present as previously healthy children with sudden onset bleeding manifestations.
• Characteristic features include generalized petechiae, purpura, and nonpalpable ecchymoses.
• Mucosal bleeding manifestations occur frequently: epistaxis, hematuria, hematochezia, menometrorrhagia, and oral oozing.
• Patients remain afebrile without systemic symptoms.
• Physical examination lacks hepatosplenomegaly, significant lymphadenopathy, bone pain, or pallor (unless significant hemorrhage occurred).
• Presence of organomegaly strongly suggests alternative diagnoses (leukemia, systemic lupus erythematosus, autoimmune lymphoproliferative syndrome).

Bleeding Severity Grading

Intracranial Hemorrhage (ICH)

• Rarest but most severe complication; incidence <1% (approximately 0.2-0.8%).
• Often occurs within 1 week of diagnosis, but 30% occur >6 months post-diagnosis.
• Platelet count <10,000/μL in 75% of ICH cases.
• Identifiable risk factors: Head trauma, concurrent hematuria, severe generalized hemorrhage, arteriovenous malformations, aspirin exposure.
• Anatomical sites: Intracerebral (77%, predominantly supratentorial) and subdural (23%).

Diagnostic Evaluation

• Diagnosis remains primarily one of exclusion.
• Complete Blood Count (CBC): Isolated severe thrombocytopenia (<100,000/μL; often <20,000/μL). Normal hemoglobin, white blood cell (WBC) count, and differential.
• Peripheral Blood Smear: Large platelets (macrothrombocytes) present, indicating increased marrow turnover. Normal erythrocyte and leukocyte morphology. Excludes pseudothrombocytopenia (platelet clumping).
• Coagulation Studies: Prothrombin time (PT), activated partial thromboplastin time (aPTT), and fibrinogen remain normal.
• Platelet Antibodies: Testing not routinely recommended due to poor specificity; antibodies absent in up to 40% of cases.
• Bone Marrow Examination:
  • Reveals normal granulopoiesis and erythropoiesis.
  • Normal or increased numbers of megakaryocytes, frequently exhibiting immature morphology.
  • Not routinely indicated for classic pediatric presentation.
  • Indications for marrow evaluation: Abnormal WBC count/differential, unexplained anemia, hepatosplenomegaly, lymphadenopathy, bone pain, failure to respond to initial intravenous immunoglobulin (IVIG) therapy, or prior to initiation of corticosteroid therapy (to definitively exclude leukemia).

Advanced Diagnostic Testing (For Persistent/Chronic Cases)

• Direct antiglobulin test (DAT/Coombs) to exclude Evans syndrome (concurrent autoimmune hemolytic anemia).
• Antinuclear antibody (ANA), double-stranded DNA to exclude systemic lupus erythematosus (SLE).
• Viral polymerase chain reaction (PCR)/serology: HIV, HCV, EBV, CMV, Parvovirus.
• Quantitative immunoglobulins to exclude common variable immunodeficiency (CVID).
• Helicobacter pylori testing.
• Thyroid function screening (TSH, free T4, antithyroid antibodies).

Differential Diagnosis

Principles Of Management

• Primary therapeutic goal: Increase platelet count sufficiently to prevent serious hemorrhage (>20,000/μL); normalization of platelet count is not the objective.
• Avoid antiplatelet medications (aspirin, nonsteroidal anti-inflammatory drugs) and restrict competitive contact sports.
• 70-80% of acute pediatric cases undergo spontaneous remission within 6 months regardless of therapy.

Observation (Watch-And-Wait Strategy)

• Recommended for children exhibiting no symptoms or mild bleeding (bruising, petechiae) regardless of absolute platelet count.
• Avoids medication toxicity, high healthcare costs, and procedural anxiety.

First-Line Pharmacologic Interventions

Reserved for moderate-to-severe mucosal bleeding or profound hemorrhagic risk.

1. Intravenous Immunoglobulin (IVIG)

• Dose: 2.0 g/kg/day over 10-12 hours
• Mechanism: Downregulates Fc-receptor mediated phagocytosis of antibody-coated platelets; saturates FcRn promoting rapid autoantibody catabolism.
• Efficacy: Rapidly increases platelet count (>20,000/μL) within 48 hours in 95% of patients. Preferred over steroids in children <2 years due to lower steroid response rates.
• Adverse Effects: Headache, emesis, aseptic meningitis, high medication cost.

2. Corticosteroids

• Dose: Prednisone 4 mg/kg/day orally for 4-5 days (without taper), or 1-2 mg/kg/day for 2-3 weeks. High-dose dexamethasone or methylprednisolone also utilized.
• Mechanism: Inhibits macrophage phagocytosis, suppresses autoantibody production, and dampens T-cell activation.
• Efficacy: Effective in 70-80% of patients; slower response compared to IVIG.
• Adverse Effects: Cushingoid facies, weight gain, hypertension, hyperglycemia, mood lability, cataracts, growth retardation (with prolonged use).

3. Intravenous Anti-D Immune Globulin

• Dose: 50-75 μg/kg administered as a single dose.
• Indications: Restricted to Rh-positive, direct antiglobulin test (DAT)-negative patients with an intact spleen.
• Mechanism: Induces mild extravascular hemolysis; resulting antibody-coated erythrocytes competitively saturate splenic Fc receptors, sparing platelets.
• Adverse Effects: Expected hemoglobin drop of 0.5-2.0 g/dL, fever, chills, headache; rare but severe intravascular hemolysis.

Emergency Interventions For Life-Threatening Hemorrhage

• Intracranial hemorrhage or massive internal bleeding dictates immediate, multimodal, aggressive intervention.
• Do not await response from single-agent therapies.
• Protocol:
  • Platelet Transfusion: Administer bolus followed by continuous infusion. Normally contraindicated due to rapid autoantibody clearance, but essential for immediate mechanical hemostasis.
  • Intravenous Methylprednisolone: 30 mg/kg/day for 1-3 days.
  • IVIG: 1 g/kg/day for 2-3 days.
  • Adjunctive Agents: Single dose of IV Anti-D (75 μg/kg), Romiplostim (10 μg/kg), or Rituximab (375 mg/m2).
  • Recombinant Factor VIIa (rFVIIa): Utilized for bypassing hemostatic defects.
  • Emergency Splenectomy: Considered if hemorrhage remains uncontrolled despite maximal medical stabilization.

Management Of Chronic And Refractory Disease

• Defined by thrombocytopenia persisting >12 months.
• Mandates rigorous reevaluation for underlying immunodeficiency or systemic autoimmunity.
• Normalizing platelet counts remains unnecessary; objective is maintaining safe counts preventing hemorrhage.

Thrombopoietin Receptor Agonists (TPO-RAs)

• First-line medical therapy for chronic pediatric ITP.
• Agents:
  • Eltrombopag: Oral administration (25-50 mg/day based on age/weight).
  • Romiplostim: Subcutaneous administration (1-10 μg/kg weekly).
• Mechanism: Directly stimulate megakaryopoiesis and platelet production via JAK2/STAT5 pathway signaling, compensating for peripheral destruction.
• Efficacy: Achieves durable platelet responses (>50,000/μL) in 64-88% of refractory patients.
• Adverse Effects: Headache, upper respiratory tract infections, transaminitis, potential bone marrow reticulin fibrosis. Eltrombopag requires monitoring for hepatotoxicity and cataracts.

Rituximab

• Chimeric monoclonal antibody targeting CD20 transmembrane antigen, resulting in profound B-cell depletion.
• Dose: 375 mg/m2 intravenously weekly for 4 consecutive weeks.
• Efficacy: Initial response rates 40-50%; long-term sustained remission in 25-30% of children. Highest curative potential noted in adolescent females.
• Adverse Effects: Infusion reactions (hives, bronchospasm), serum sickness, transient hypogammaglobulinemia, rare reactivation of latent viral infections.

Splenectomy

• Eradicates primary site of autoantibody synthesis and platelet destruction.
• Indications: Strictly reserved for severe chronic ITP (>1 year duration) unresponsive to medical therapy with severely impaired quality of life, or acute life-threatening hemorrhage refractory to maximal medical therapy. Extremely rare in children <5 years.
• Efficacy: Induces complete remission in 64-88% of pediatric patients.
• Complications: Lifelong susceptibility to overwhelming postsplenectomy infection (OPSI) by encapsulated organisms, increased stroke/thrombosis risk, and subsequent pulmonary hypertension.
• Prerequisites: Mandatory preoperative immunization (pneumococcal, meningococcal, Haemophilus influenzae) and lifelong postoperative penicillin prophylaxis.

Second-Line Immunosuppressive Therapies

• Mycophenolate Mofetil / Sirolimus (Rapamycin): Highly effective for ITP secondary to Evans syndrome or Autoimmune Lymphoproliferative Syndrome (ALPS).
• Alternative Agents: Azathioprine, Danazol (avoid in prepubertal children due to premature epiphyseal closure), Dapsone, Cyclosporine, Cyclophosphamide, and Vincristine demonstrate variable efficacy in highly refractory cases.