USMLE Guide: Hematology of Leukemia

Introduction

Leukemia is a group of malignant disorders characterized by the uncontrolled proliferation of white blood cells in the bone marrow. This USMLE guide aims to provide a comprehensive overview of the hematology of leukemia, including its classification, clinical features, diagnostic tests, and treatment options.

Classification

1. Acute Leukemias:
   • Acute Lymphoblastic Leukemia (ALL)
   • Acute Myeloid Leukemia (AML)
2. Chronic Leukemias:
   • Chronic Lymphocytic Leukemia (CLL)
   • Chronic Myeloid Leukemia (CML)

Clinical Features

1. Acute Leukemias:
   • Fatigue, pallor, and weakness due to anemia
   • Bone pain and tenderness
   • Increased susceptibility to infections
   • Bleeding tendencies (e.g., petechiae, ecchymoses)
2. Chronic Leukemias:
   • Often asymptomatic initially
   • Fatigue, weight loss, and night sweats
   • Splenomegaly and hepatomegaly
   • Lymphadenopathy

Diagnostic Tests

1. Complete Blood Count (CBC):
   • Leukocytosis with immature cells (blasts) in acute leukemias
   • Leukocytosis or lymphocytosis in chronic leukemias
   • Anemia and thrombocytopenia may be present
2. Peripheral Blood Smear:
   • Presence of blasts in acute leukemias
   • Smudge cells in chronic lymphocytic leukemia (CLL)
   • Basophilia and increased granulocyte precursors in chronic myeloid leukemia (CML)
3. Bone Marrow Aspiration and Biopsy:
   • Gold standard for diagnosis and classification
   • Increased blast cells in acute leukemias
   • Lymphocytic infiltration in CLL
   • Philadelphia chromosome (BCR-ABL fusion gene) in CML
4. Flow Cytometry:
   • Immunophenotyping to determine the lineage of leukemic cells
   • Helps in distinguishing between ALL and AML

Treatment Options

1. Chemotherapy:
   • Induction therapy to achieve remission
   • Consolidation therapy to eliminate residual leukemic cells
   • Maintenance therapy to prevent relapse
2. Stem Cell Transplantation:
   • Allogeneic transplantation for younger patients with high-risk disease
   • Autologous transplantation for eligible patients in remission
3. Targeted Therapy:
   • Tyrosine kinase inhibitors (e.g., imatinib) for CML patients with the Philadelphia chromosome
   • Monoclonal antibodies (e.g., rituximab) for CLL patients
4. Supportive Care:
   • Blood transfusions and growth factors to manage anemia and thrombocytopenia
   • Prophylactic antibiotics to prevent infections

Conclusion

Leukemia is a heterogeneous group of malignant disorders affecting the white blood cells. Understanding the classification, clinical features, diagnostic tests, and treatment options is essential for medical students preparing for the USMLE.