A 58-year-old man with a 3-year history of essential thrombocythemia (ET) presents with acute onset left leg pain, swelling, and cyanosis of the toes. Platelet count is 680 × 10⁹/L (baseline ~550 × 10⁹/L despite hydroxyurea therapy). Doppler ultrasound confirms acute thrombosis of the left popliteal and femoral veins. Arterial blood gas shows mild hypoxemia. He denies recent immobilization, surgery, or malignancy. JAK2 V617F mutation is positive. What is the most appropriate immediate management?

Explanation

## Clinical Context: Thrombosis in Myeloproliferative Neoplasm (MPN) **Key Point:** Thrombotic events in essential thrombocythemia (ET), particularly in the setting of JAK2 V617F positivity, represent a **medical emergency** requiring simultaneous cytoreduction and anticoagulation. ## Pathophysiology of Thrombosis in ET 1. **Platelet dysfunction:** Abnormal platelet aggregation and increased prothrombotic activity (tissue factor, phosphatidylserine exposure) 2. **Elevated platelet count:** Mechanical obstruction and increased thrombin generation 3. **JAK2 V617F mutation:** Associated with higher thrombotic risk (~2-fold) and more aggressive disease 4. **Microvascular thrombosis:** Characteristic of ET, causing digital ischemia and acral cyanosis ## Immediate Management Algorithm ```mermaid flowchart TD A[ET with acute thrombosis]:::outcome --> B{Platelet count > 600 × 10⁹/L?}:::decision B -->|Yes| C[URGENT cytoreduction]:::urgent C --> D[Hydroxyurea increase or anagrelide]:::action B -->|No| E[Anticoagulation alone may suffice]:::action C --> F[Simultaneous anticoagulation]:::action F --> G[UFH or LMWH]:::action G --> H[Transition to warfarin INR 2-3]:::action H --> I[Long-term anticoagulation + cytoreduction]:::outcome ``` **High-Yield:** In ET with thrombosis: - **Platelet count >600 × 10⁹/L** = cytoreduction is part of thrombosis management, not just prevention - **Cytoreduction reduces viscosity** and restores normal platelet function - **Anticoagulation alone is insufficient** — platelet-lowering is mandatory ## Why This Patient Needs Dual Therapy | Intervention | Rationale | |--------------|----------| | **UFH (not warfarin alone)** | Rapid anticoagulation; UFH can be reversed if bleeding occurs; allows assessment of response | | **Hydroxyurea increase** | Reduces platelet count from 680 to <400 × 10⁹/L, reducing thrombotic risk; improves platelet function | | **NOT aspirin monotherapy** | Aspirin is for **prevention** in asymptomatic ET; inadequate for acute thrombosis | | **NOT thrombolysis alone** | Thrombolysis increases bleeding risk in thrombocytosis; reserved for life-threatening PE/massive MI | **Clinical Pearl:** Microvascular thrombosis (digital ischemia, erythromelalgia) in ET responds dramatically to cytoreduction within hours to days — a diagnostic clue that platelet-lowering is the key intervention. ## Subsequent Management 1. **Continue UFH** until platelet count <400 × 10⁹/L and clinical improvement (usually 3–7 days) 2. **Transition to warfarin** (target INR 2–3) or DOAC once stable 3. **Maintain long-term cytoreduction** (hydroxyurea or anagrelide) to keep platelets <400 × 10⁹/L 4. **Assess for other thrombotic risk factors** (JAK2 V617F positivity, age >60, prior thrombosis) — all present here, indicating high-risk ET **Mnemonic for ET thrombosis management:** **CHAP** - **C**ytoreduction (hydroxyurea, anagrelide) - **H**eparin (UFH or LMWH) - **A**nticoagulation (transition to warfarin) - **P**latelet target <400 × 10⁹/L [cite:Harrison 21e Ch 175]