Hematology — L6: Acute Leukemia

📚 Lecture Overview

This lecture covers acute leukemia, a fatal group of hematological malignancies characterized by the uncontrolled proliferation of immature hematopoietic cells in the bone marrow and peripheral blood. It details the classification, clinical features, diagnosis, and distinct management strategies for both Acute Myeloid Leukemia (AML) and Acute Lymphoblastic Leukemia (ALL). Understanding these concepts is critical for recognizing hematological emergencies and administering appropriate life-saving treatments.

🎯 Key Concepts & Definitions

Acute Leukemia: Proliferation and accumulation of immature hematopoietic cells (myeloid or lymphoid) that fail to differentiate, suppressing normal hematopoiesis.
AML (Acute Myeloid Leukemia): Clonal malignant disease of myeloid progenitor cells; most common acute leukemia in adults, strongly linked to age over 60.
ALL (Acute Lymphoblastic Leukemia): Malignancy of lymphoid precursors; the most common cancer and second leading cause of death in children under 15.
Leukostasis: Medical emergency caused by hyperleukocytosis (>50,000 blasts/μL) leading to pulmonary and CNS ischemic or hemorrhagic complications.
Tumor Lysis Syndrome (TLS): Life-threatening metabolic abnormalities (hyperuricemia, hyperkalemia, hyperphosphatemia, hypocalcemia) resulting from rapid tumor cell destruction.
Philadelphia Chromosome: Cytogenetic abnormality ($t(9;22)$) resulting in constitutive activation of abl; present in ~20% of adult ALL cases and confers a poor prognosis.
Auer Rods: Pathognomonic rod-shaped cytoplasmic structures found in myeloblasts, used to distinguish AML from ALL under light microscopy.

📖 Main Content

Introduction & Pathophysiology

Acute leukemia involves uncontrolled proliferation of immature cells that replace and suppress normal erythroid, myeloid, and megakaryocytic lineages.
Untreated acute leukemia is fatal in weeks.
AML Epidemiology: Incidence increases with age; most patients are over 60 years.
Etiology and Risk Factors:
Environmental: Benzene, ionizing radiation, herbicides.
Genetic disorders: Down syndrome, Fanconi anemia, Bloom syndrome.
Pre-existing disorders: Myelodysplastic syndromes (MDS), paroxysmal nocturnal hemoglobinuria.
Treatment-associated: Alkylating agents, topoisomerase II inhibitors, radiotherapy.

Clinical Picture

Symptoms are divided into three main categories:
- General Symptoms: Reduced performance status, fever, night sweats, fatigue, weight loss, and bone pain.
- Impairment of Normal Hematopoiesis:
- Anemia: Weakness, fatigue, tachycardia, pallor.
- Thrombocytopenia: Bleeding tendency, petechiae, ecchymosis, epistaxis.
- Granulocytopenia: Skin infections, pneumonia, sepsis.
- Leukemic Cell Proliferation & Infiltration:
- Hepatosplenomegaly.
- Chloroma: Extramedullar tumorous manifestation (common in AML M4/M5 with gingival hyperplasia and skin infiltrates).
- CNS involvement and lymphadenopathy (especially mediastinal lymphadenopathy in T-cell ALL).

Diagnosis & Investigations

Diagnostic Criteria: Requires the presence of ≥20% blasts in peripheral blood and/or bone marrow (unless specific WHO-defined recurrent cytogenetic abnormalities are present).
Distinguishing AML vs. ALL:
AML: Presence of Auer rods and cytoplasmic granules under light microscopy.
ALL: Absence of Auer rods; categorized by FAB into L1, L2, L3 and by cell surface markers (CALLA, pre-B, T-cell).
Laboratory Tests: Complete blood count, coagulation parameters (screening for DIC, especially in AML M3 / APL), liver and renal function, LDH, and HLA typing.
Bone Marrow Evaluation: Aspiration for morphology, cytochemistry, and cytogenetics; lumbar puncture for CNS evaluation.

Treatment Strategies

Supportive Care:
Tumor lysis prophylaxis: Fluid replacement, urine alkalization, allopurinol, or rasburicase.
Blood product support: Keep platelets >50,000/μL in DIC and AML M3.
Immediate management of leukostasis with hydroxyurea or leukapheresis.
AML Treatment:
Induction: Standard "7 & 3" regimen (7 days of cytarabine + 3 days of an anthracycline).
Postremission: Intensification and allogeneic stem cell transplantation for poor/intermediate risk cytogenetics.
ALL Treatment (4 Phases):
Remission Induction: Combination of prednisone, vincristine, daunorubicin, and asparaginase.
Consolidation: Rotating intensive multi-drug chemotherapy.
CNS Prophylaxis: Intrathecal methotrexate and/or cranial irradiation.
Maintenance: Prolonged daily 6-mercaptopurine and weekly methotrexate with monthly pulses for 2-3 years.

📊 Visual Learning

flowchart TD A[Suspicious CBC] --> B[Bone Marrow Aspiration] B --> C{Blasts Greater 20 Percent} C -->|Yes| D[Identify Blast Type] C -->|No| E[Check WHO Cytogenetics] D -->|Auer Rods Present| F[Diagnose AML] D -->|No Auer Rods| G[Diagnose ALL] E -->|Specific Mutation| F E -->|Specific Mutation| G

mindmap root("Acute Leukemia Complications") "Bone Marrow Failure" "Anemia" "Thrombocytopenia" "Granulocytopenia" "Metabolic Emergencies" "Tumor Lysis Syndrome" "Hyperuricemia" "Hyperkalemia" "Vascular and Organ Infiltration" "Leukostasis" "DIC in APL M3" "CNS Infiltration"

💡 Important Points to Remember

Diagnostic Threshold: Diagnosis of acute leukemia requires at least 20% blasts in the blood or bone marrow (unless specific high-risk cytogenetics are present).
Hallmark of AML: The presence of Auer rods in blasts is diagnostic for AML and absent in ALL.
Standard AML Induction: The "7 & 3" regimen combines 7 days of cytarabine with 3 days of an anthracycline.
APL Emergency: AML M3 (Acute Promyelocytic Leukemia) is heavily associated with Disseminated Intravascular Coagulation (DIC) and requires urgent intervention.
Hyperleukocytosis Danger: Leukocyte counts >50,000/μL trigger leukostasis, threatening pulmonary and CNS microcirculation.
Tumor Lysis Syndrome: Rapid cell destruction leads to hyperkalemia, hyperphosphatemia, hyperuricemia, and hypocalcemia.
Pediatric vs. Adult ALL: ALL is the most common cancer in children (ages 2-10), whereas AML incidence sharply rises after age 60.
Poor Prognosis Markers: The Philadelphia chromosome ($t(9;22)$) in adult ALL and the $t(8;14)$ mutation in L3-ALL indicate a poor prognosis.
ALL Treatment Duration: Maintenance therapy for ALL is prolonged, lasting 2-3 years using 6-mercaptopurine and methotrexate.
Common Confusion: Do not confuse CML blast crisis with de novo acute leukemia; review patient history and cytogenetics (Philadelphia chromosome is hallmark of CML).

⚠️ Common Exam Questions

Examiners frequently test the differentiation between AML and ALL based on morphology (Auer rods), specific cytogenetic translocations (Philadelphia chromosome in ALL vs others), and management protocols.

MCQ Trick Traps:
- Trap: Examiners will state a patient has 15% blasts in the bone marrow and try to trick you into diagnosing acute leukemia. Rule: You generally need ≥20% blasts unless specific WHO cytogenetic criteria are met.
- Trap: Confusing the induction regimens; attributing the "7 & 3" regimen to ALL instead of AML.
- Trap: Forgetting that AML M3 is uniquely associated with DIC and requires strict platelet transfusion thresholds (>50,000/μL).

📝 Quick Review Checklist

I can define acute leukemia and its primary pathophysiology
I understand the clinical presentation triad of marrow failure, organ infiltration, and general symptoms
I can differentiate between AML and ALL using microscopy (Auer rods) and clinical features
I know the diagnostic threshold of blast percentages
I can list key complications like leukostasis, DIC, and tumor lysis syndrome
I understand the four treatment phases of ALL and the "7 & 3" induction protocol for AML
I know the prognostic significance of the Philadelphia chromosome

📚 Hematology — L6: Acute Leukemia