A 38-year-old woman with acute promyelocytic leukemia (APL) presents to the emergency department with spontaneous bleeding from gums and petechiae over the trunk. She was diagnosed 3 days ago and started on ATRA and arsenic trioxide. Blood pressure is 95/58 mmHg, heart rate 118/min. Laboratory findings: Hb 7.2 g/dL, platelets 18,000/μL, PT 18 sec (control 12), aPTT 52 sec (control 36), fibrinogen 95 mg/dL (normal 200–400), D-dimer markedly elevated. Peripheral blood shows abnormal promyelocytes with Auer rods. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: DIC in APL ### Pathophysiologic Basis **Key Point:** APL is the hematologic malignancy most strongly associated with DIC, occurring in 80–90% of cases at presentation or during early treatment (differentiation syndrome). APL blasts contain high levels of tissue factor (TF) and cancer procoagulant, which activate the extrinsic coagulation pathway. Additionally, ATRA and arsenic trioxide trigger differentiation and release of these procoagulants, precipitating fulminant DIC. ### Diagnostic Criteria Met | Parameter | Finding | Significance | |-----------|---------|---------------| | Thrombocytopenia | 18,000/μL | Consumption of platelets | | Prolonged PT/aPTT | 18 sec / 52 sec | Consumption of clotting factors | | Hypofibrinogenemia | 95 mg/dL | Fibrinogen consumption | | Elevated D-dimer | Markedly ↑ | Excessive fibrin formation & degradation | | Bleeding manifestations | Spontaneous gum bleeding, petechiae | Microthrombi & factor depletion | | Hemodynamic instability | BP 95/58, HR 118 | Sepsis-like state from DIC | **High-Yield:** The combination of **APL diagnosis + coagulopathy + thrombocytopenia + hypofibrinogenemia + elevated D-dimer** is pathognomonic for DIC. ### ISTH Scoring for DIC This patient scores ≥5 points (diagnostic threshold): - Platelet count 18,000: +1 point - D-dimer/FDP elevation: +3 points (markedly elevated) - PT prolongation: +1 point - Fibrinogen <100 mg/dL: +1 point - **Total: ≥6 points → overt DIC confirmed** ### Management Implications 1. **Aggressive supportive care:** Fresh frozen plasma (FFP), cryoprecipitate, platelet transfusion 2. **Treat underlying APL:** Continue ATRA/arsenic (do NOT stop — differentiation is curative) 3. **Anticoagulation:** Low-dose heparin may be considered in some protocols to prevent thrombotic complications 4. **Monitor:** Serial PT, aPTT, fibrinogen, platelet count, D-dimer q6–12h **Clinical Pearl:** Unlike sepsis-induced DIC, APL-DIC responds well to definitive treatment of the leukemia itself; mortality has dropped from >80% to <10% with modern protocols combining ATRA, arsenic, and chemotherapy.