A 58-year-old man with newly diagnosed pancreatic cancer presents with acute onset of bleeding from multiple sites: hemoptysis, hematuria, and severe epistaxis. Laboratory investigations reveal: platelet count 45,000/µL, PT 18 sec (normal 12–14), aPTT 48 sec (normal 25–35), fibrinogen 95 mg/dL (normal 200–400), D-dimer 8.5 µg/mL (normal <0.5). Peripheral blood smear shows schistocytes. What is the primary mechanism of thrombocytopenia in this patient?

Explanation

## Clinical Diagnosis: Disseminated Intravascular Coagulation (DIC) **Key Point:** This patient has DIC—a life-threatening syndrome of simultaneous, uncontrolled activation of coagulation and fibrinolysis, leading to consumption of platelets, clotting factors, and fibrinogen. ## Pathophysiology of DIC ```mermaid flowchart TD A[Tissue Factor released<br/>Pancreatic cancer/sepsis/trauma]:::urgent --> B[Extrinsic pathway activation] B --> C[Thrombin generation] C --> D[Platelet activation & aggregation] D --> E[Microthrombi formation<br/>in microvasculature]:::urgent E --> F[Mechanical RBC damage<br/>Schistocytes]:::outcome C --> G[Fibrin deposition] G --> H[Consumption of:<br/>Platelets, Factors V/VIII, Fibrinogen]:::urgent H --> I[Secondary fibrinolysis] I --> J[Elevated D-dimer<br/>Elevated FDPs]:::outcome E --> K[End-organ ischemia<br/>Bleeding + Thrombosis]:::urgent ``` ## Why Consumption is the Primary Mechanism **High-Yield:** DIC is characterized by **simultaneous activation of coagulation AND fibrinolysis**, leading to: 1. **Platelet consumption** → microthrombi trap platelets in microvasculature 2. **Factor consumption** → PT and aPTT prolonged (factors II, V, VII, VIII, X depleted) 3. **Fibrinogen consumption** → low fibrinogen (< 100 mg/dL) 4. **Fibrin formation and breakdown** → markedly elevated D-dimer and fibrin degradation products (FDPs) 5. **Mechanical hemolysis** → schistocytes from passage through fibrin strands ## Diagnostic Criteria for DIC (ISTH Score) | Parameter | Finding | Points | |-----------|---------|--------| | Platelet count | 45,000 | 1 | | D-dimer/FDP | Markedly elevated (8.5) | 3 | | PT prolongation | 18 sec (4 sec above normal) | 1 | | Fibrinogen | 95 mg/dL (low) | 1 | | **Total score** | | **6 (≥5 = overt DIC)** | **Clinical Pearl:** The **pentad of DIC** = thrombocytopenia + prolonged PT/aPTT + low fibrinogen + elevated D-dimer + schistocytes. This patient has all five. ## Triggers of DIC in This Case - **Pancreatic cancer** (tissue factor release from malignant cells) - Other common triggers: sepsis, trauma, acute leukemia, obstetric emergencies (placental abruption, amniotic fluid embolism) **Mnemonic: STOP DIC** — Sepsis, Trauma, Obstetric emergencies, Pancreatic/malignancy, Disseminated intravascular coagulation.