Thrombocytopenia

Thrombocytopenia - Platelet Plunge Primer

• Definition: Platelet count < 150,000/μL.
• Broad Etiologies:
  • Decreased Production:
    • Bone marrow disorders (aplastic anemia, leukemia, MDS).
    • Drugs (chemotherapy), infections (HIV, HCV).
    • Nutritional deficiencies (B12, folate).
  • Increased Destruction:
    • Immune: ITP, drug-induced (e.g., heparin - HIT), SLE.
    • Non-immune: DIC, TTP, HUS, HELLP syndrome.
  • Sequestration: Hypersplenism (e.g., cirrhosis, portal hypertension).
  • Dilutional: Massive transfusions.

⭐ Immune Thrombocytopenic Purpura (ITP) is often triggered by a preceding viral infection, especially in children, and involves autoantibodies against platelet glycoproteins like GPIIb/IIIa or GPIb-IX.

Etiology - The Platelet Pilferers

• Decreased Production (Marrow Aplasia/Infiltration/Suppression)
  • Congenital: Fanconi anemia, TAR syndrome, WAS, Amegakaryocytic thrombocytopenia.
  • Acquired: Aplastic anemia, Leukemia/Lymphoma, Myelodysplasia, Viral (HIV, CMV, EBV, Parvo B19), Drugs (chemo, valproate, linezolid), Nutritional (B12/Folate).
• Increased Destruction (Peripheral Consumption)
  • Immune-Mediated:
    • ITP (Immune Thrombocytopenic Purpura): Most common in children.

    ⭐ ITP is the most common cause of isolated thrombocytopenia in an otherwise healthy child, typically occurring 1-4 weeks after a viral infection.

    • NAIT (Neonatal Alloimmune Thrombocytopenia): Maternal IgG vs fetal platelets.
    • Autoimmune (SLE, Evans Syndrome).
    • Drug-Induced (heparin, quinine, sulfonamides, vancomycin).
  • Non-Immune Mediated:
    • DIC (Disseminated Intravascular Coagulation).
    • HUS (Hemolytic Uremic Syndrome)/TTP (Thrombotic Thrombocytopenic Purpura).
    • Kasabach-Merritt Syndrome.
• Sequestration: Hypersplenism.
• Dilutional: Massive transfusions.

Clinical Clues & Dx - Spotting the Shortage

• Clinical Signs: Often asymptomatic. Mucocutaneous bleeding: petechiae, purpura, ecchymoses. Epistaxis, gingival, GI/GU bleeding. Severe: ICH risk. Splenomegaly? (sequestration/destruction). No lymphadenopathy/fever in isolated ITP.
• Key Investigations:
  • CBC & Peripheral Smear (PBS): Confirms true thrombocytopenia (platelets <150,000/µL), rules out pseudothrombocytopenia (EDTA clumps). Platelet morphology: large (ITP), small (WAS). Schistocytes? (TTP/HUS). Blasts? (Leukemia).
  • Coagulation: PT/aPTT normal in isolated thrombocytopenia.
  • Bone Marrow Exam (BME): Not routine. For atypical cases, other cytopenias, failed therapy, pre-splenectomy. ITP: normal/↑ megakaryocytes.

⭐ Petechiae (pinpoint, non-blanching spots) are hallmark of thrombocytopenia; large bruises/joint bleeds suggest coagulopathy.

Key Syndromes - Syndrome Showdown: ITP, HUS, NAIT

• Immune Thrombocytopenic Purpura (ITP)

  • Patho: Anti-GpIIb/IIIa IgG autoantibodies.
  • Onset: Acute (children, post-viral), Chronic (adults).
  • Features: Isolated thrombocytopenia, mucocutaneous bleeding. Normal spleen.
  • Labs: ↓ Platelets, giant platelets. Marrow: ↑ megakaryocytes.
  • Rx: Observation, Steroids, IVIG.

• Hemolytic Uremic Syndrome (HUS)

  • Patho: Endothelial damage by Shiga toxin (E.coli O157:H7) or complement dysregulation (atypical).
  • Onset: Children <5 yrs (typical).
  • Features: Triad: MAHA, Thrombocytopenia, AKI. Often post-bloody diarrhea.
  • Labs: ↓ Platelets, schistocytes, ↑LDH, ↑Creatinine.
  • Rx: Supportive. Plasma exchange (atypical).

  ⭐ HUS: Avoid antibiotics for E.coli O157:H7 gastroenteritis; may ↑ toxin release & HUS risk.

• Neonatal Alloimmune Thrombocytopenia (NAIT)

  • Patho: Maternal IgG anti-HPA-1a (common) vs fetal platelets.
  • Onset: Neonates (hours post-birth).
  • Features: Severe thrombocytopenia; petechiae, purpura. ICH risk ~10-20%.
  • Labs: ↓ Neonatal platelets, normal maternal count.
  • Rx: IVIG, HPA-matched/washed maternal platelets.

High‑Yield Points - ⚡ Biggest Takeaways

• Immune Thrombocytopenia (ITP): Most common acquired cause in children, often post-viral, usually self-limiting; observe or treat if severe.
• Wiskott-Aldrich Syndrome (X-linked): Microthrombocytopenia (small platelets), eczema, recurrent infections.
• Bernard-Soulier Syndrome: Giant platelets, defective adhesion (GP Ib/IX/V deficiency), AR inheritance.
• Glanzmann Thrombasthenia: Normal platelet count, defective aggregation (GP IIb/IIIa deficiency), AR inheritance.
• Neonatal Alloimmune Thrombocytopenia (NAIT): Maternal IgG anti-platelet antibodies (e.g., anti-HPA-1a) crossing placenta, risk of intracranial hemorrhage.
• Kasabach-Merritt Syndrome: Consumptive thrombocytopenia associated with large vascular tumors (e.g., kaposiform hemangioendothelioma).