A 28-year-old woman from Delhi presents with a 3-week history of progressive fatigue, petechiae on her legs, and spontaneous bleeding from her gums. On examination, she is pale with hepatomegaly (3 cm below costal margin) and splenomegaly (4 cm). Blood pressure is 110/70 mmHg. Complete blood count shows hemoglobin 7.2 g/dL, WBC 85,000/μL (85% blasts), and platelets 18,000/μL. Bone marrow aspirate reveals >90% blasts with Auer rods. Flow cytometry shows CD13+, CD33+, HLA-DR+, and MPO+ blasts. What is the most likely diagnosis?

Explanation

## Diagnosis: Acute Myeloid Leukemia with Maturation (AML-M2) ### Clinical Presentation The patient presents with classic acute leukemia features: pancytopenia (anemia, thrombocytopenia), high WBC count with blasts, hepatosplenomegaly, and hemorrhagic manifestations. The 3-week progressive course is typical. ### Morphologic & Immunophenotypic Findings **Key Point:** The presence of **Auer rods** (pathognomonic for myeloid differentiation) combined with >90% blasts confirms acute myeloid leukemia. **High-Yield:** The immunophenotype CD13+, CD33+ (myeloid markers), HLA-DR+, and MPO+ (myeloperoxidase positivity) indicates myeloid lineage with some maturation. ### FAB Classification Correlation | Feature | AML-M1 (Undifferentiated) | AML-M2 (With maturation) | AML-M5 (Monocytic) | AML-M7 (Megakaryoblastic) | |---------|---------------------------|------------------------|-------------------|-------------------------| | **Blasts** | >90%, minimal maturation | 30–89% blasts + maturing forms | >80% monocytic blasts | Megakaryoblasts | | **Auer Rods** | May be present | Frequently present | Rare | Absent | | **Myeloid markers** | CD13, CD33 | CD13, CD33 | CD14, CD15 | CD41, CD42 | | **MPO** | Positive | Positive | Positive | Negative | | **Monocytic markers** | Absent | Absent | CD14+, CD15+ | Absent | **Clinical Pearl:** The combination of Auer rods + CD13/CD33 positivity + presence of some maturing myeloid forms (implied by "with maturation" classification) points to AML-M2 rather than the more immature AML-M1. ### Why AML-M2 is Correct 1. **Auer rods** are a hallmark of myeloid differentiation and are most common in AML-M2 and APL. 2. **CD13/CD33 positivity** confirms myeloid origin. 3. **MPO positivity** indicates myeloid lineage. 4. The FAB classification "with maturation" (M2) implies presence of maturing forms alongside blasts, which is the defining feature. ### Differential Considerations **Acute Promyelocytic Leukemia (APL / AML-M3):** While APL also has Auer rods and myeloid markers, APL is characterized by abnormal promyelocytes with heavy granulation and multiple Auer rods ("faggot cells"). The morphology and immunophenotype here are more consistent with M2. Additionally, APL typically presents with severe coagulopathy (DIC) due to release of procoagulant from abnormal granules—not mentioned here. **Acute Monocytic Leukemia (AML-M5):** Would show CD14+ and CD15+ (monocytic markers), not the myeloid-predominant phenotype seen here. Auer rods are rare in M5. **Acute Megakaryoblastic Leukemia (AML-M7):** Would be CD41+ and CD42+ (platelet glycoproteins), and MPO would be negative. This patient's MPO+ and CD13/CD33+ phenotype excludes M7. [cite:Robbins 10e Ch 13]