A 52-year-old man from Delhi presents to the emergency department with severe headache, confusion, and visual disturbances for 2 days. He has a history of chronic myeloid leukemia diagnosed 5 years ago, currently on imatinib therapy. Vital signs show blood pressure 160/100 mmHg and heart rate 110/min. Laboratory investigations reveal WBC 450,000/μL, hemoglobin 9.5 g/dL, and platelet count 850,000/μL. Peripheral blood smear shows numerous myelocytes, metamyelocytes, and occasional blasts with Auer rods. Retinal examination shows flame-shaped hemorrhages and cotton-wool spots. What is the most likely diagnosis?

Explanation

## Clinical Context and Pathophysiology This patient with CML presents with an acute neurological emergency in the setting of **extreme leukocytosis** (WBC 450,000/μL). The key finding is the combination of: - Severe hyperleukocytosis - CNS symptoms (headache, confusion, visual disturbances) - Retinal hemorrhages and cotton-wool spots - Myeloid predominance on smear (myelocytes, metamyelocytes) **Key Point:** Leukostasis is a medical emergency caused by **extreme leukocytosis** (typically >100,000/μL in AML or >200,000/μL in ALL/CML) leading to microvascular occlusion and hemorrhage. ## Mechanism of Leukostasis ```mermaid flowchart TD A[Extreme Leukocytosis]:::outcome --> B[Increased Blood Viscosity]:::outcome B --> C[Microvascular Occlusion]:::outcome C --> D{Vascular Bed Affected?}:::decision D -->|Cerebral| E[CNS Leukostasis:<br/>Headache, confusion,<br/>seizures, stroke]:::urgent D -->|Pulmonary| F[Pulmonary Leukostasis:<br/>Dyspnea, hypoxia,<br/>pulmonary hemorrhage]:::urgent D -->|Retinal| G[Hemorrhagic Retinopathy:<br/>Flame hemorrhages,<br/>cotton-wool spots]:::urgent E --> H[Cytoreduction + Hydroxyurea]:::action F --> H G --> H ``` ## Differential Diagnosis: Smear Findings | Feature | Leukostasis | Blast Crisis CML | TTP | Hypertensive Retinopathy | |---------|-------------|------------------|-----|------------------------| | **WBC count** | >100,000 (myeloid series) | >100,000 (>20% blasts) | Normal/↓ | Normal | | **Myelocytes/Metamyelocytes** | Abundant | Present + increased blasts | Absent | Absent | | **Auer rods** | Rare | May be present | Absent | Absent | | **Platelets** | Often elevated | ↓ or ↑ | **Markedly ↓** | Normal | | **Schistocytes** | Absent | Absent | **Present** | Absent | | **Retinal findings** | Hemorrhages, cotton-wool spots | Hemorrhages (from thrombocytopenia) | Microangiopathic changes | Flame hemorrhages, exudates | | **Hemolysis markers** | Normal | Normal | **Elevated LDH, ↓ haptoglobin** | Normal | **Clinical Pearl:** The presence of **flame-shaped hemorrhages and cotton-wool spots** in the retina is characteristic of leukostasis-induced retinopathy, not simple hypertensive retinopathy. Hypertensive retinopathy shows **hard exudates, papilledema, and arteriovenous nicking**—not flame hemorrhages. ## Why This Is NOT Blast Crisis While the smear shows myelocytes and metamyelocytes, the **absence of >20% blasts** argues against blast crisis. Additionally, blast crisis typically presents with **thrombocytopenia** (not thrombocytosis) and **more severe anemia**. The acute presentation with CNS and retinal symptoms is more consistent with **leukostasis** than blast transformation. **High-Yield:** Leukostasis is a medical emergency requiring **immediate cytoreduction** (hydroxyurea, low-dose cytarabine) and **phlebotomy** (cautiously, as it may paradoxically worsen viscosity). Do NOT transfuse RBCs unless Hb <7 g/dL, as this increases viscosity further. **Mnemonic — Leukostasis Presentation:** **CHOP** — CNS symptoms, Headache, Ocular (retinal hemorrhages), Pulmonary symptoms ## Management 1. **Immediate cytoreduction:** Hydroxyurea 50–100 mg/kg/day or low-dose cytarabine 2. **Avoid RBC transfusion** (increases viscosity) 3. **Cautious phlebotomy** if Hb >10 g/dL 4. **Allopurinol** to prevent tumor lysis syndrome 5. **Monitor for DIC and acute kidney injury**