Diseases of Hematopoietic Cells & Lymph Nodes – Core Vocabulary

Hematopoiesis Basics

All blood cells arise from multipotential hematopoietic stem cells that diverge into common myeloid and common lymphoid progenitors. Differentiation is regulated by cytokines such as \text{SCF}, \text{Epo}, \text{TPO}, \text{GM\text{-}CSF}, and interleukins. Mutations in FLT3, RUNX1, NPM1, and JAK2 commonly disrupt myeloid lineage, whereas NOTCH1, BCL2, BCL6, MYC, and IgH translocations affect lymphoid cells.

Key Hematopoietic Organs

Red marrow within bone cavities houses hematopoietic and mesenchymal stem-cell niches arranged around a sinusoidal network with stromal support. Extramedullary hematopoiesis may re-emerge in liver and spleen during disease. Peripheral lymphoid organs – lymph nodes, spleen, and thymus – organize immune cell maturation, antigen filtration, and blood cell destruction.

White Cell Disorders

Leukopenia (notably neutropenia) reflects reduced or destroyed granulocytes; drug toxicity is the leading cause of severe agranulocytosis. Leukocytosis represents reactive or neoplastic expansion of leukocytes; cell numbers depend on marrow pool size, release rate, marginating fraction, and tissue egress. Lymphadenitis denotes reactive node enlargement driven by immune activation. Hemophagocytic lymphohistiocytosis combines macrophage hyperactivity, cytopenias, hyperferritinemia, and disseminated coagulation.

Leukemias Overview & Key Entities

Leukemia is a clonal marrow malignancy causing uncontrolled leukocyte proliferation and marrow failure. Classification pairs cell lineage (lymphoid vs myeloid) with tempo (acute vs chronic).

Acute Lymphoblastic Leukemia (ALL) arises from precursor B/T cells, is the most common childhood cancer, and features NOTCH1 or ETV6\text{-}RUNX1 lesions; presentation includes marrow failure or mediastinal mass.

Chronic Lymphocytic Leukemia (CLL) is an indolent mature B-cell disease with CD5^+ CD23^+ cells and “smudge” cells; may transform to aggressive lymphoma (Richter syndrome).

Acute Myeloid Leukemia (AML) shows >20\% myeloid blasts, often with Auer rods; the t(15;17) variant (APML) carries DIC risk but responds to ATRA therapy.

Chronic Myeloid Leukemia (CML) results from BCR\text{-}ABL1 fusion (Philadelphia chromosome) and is treated with tyrosine-kinase inhibitors.

Lymphomas Overview & Key Entities

Lymphomas are malignant proliferations of lymphocytes forming masses. Hodgkin lymphoma is defined by Reed–Sternberg cells, contiguous nodal spread, bimodal age peaks, and frequent EBV association. Non-Hodgkin lymphomas are usually B-cell, exhibit extranodal disease and non-contiguous spread.

Follicular Lymphoma carries t(14;18) leading to BCL2 over-expression; presents with indolent nodular node enlargement. Diffuse Large B-cell Lymphoma is the most common NHL, rapidly enlarges nodal or extranodal masses, and often harbors BCL6, BCL2, or MYC alterations. Burkitt Lymphoma shows t(8;14)–MYC translocation, “starry-sky” histology, and endemic jaw or sporadic abdominal disease with strong EBV link.

Plasma Cell Neoplasms

Multiple Myeloma is a bone-marrow–based plasma-cell tumor featuring lytic bone lesions, hypercalcemia, renal failure, and monoclonal M protein or Bence-Jones light chains. Genetic events target the IgH locus with partners such as cyclin D1 or MYC; TP53 loss predicts poor prognosis.

Anemia Fundamentals

Anemia denotes decreased red-cell mass or hemoglobin and arises from impaired production, blood loss, or increased destruction. Reticulocyte index differentiates hypoproliferative (

Hemorrhagic & Platelet Disorders

Hemostasis requires adequate platelets, intact vessels, and coagulation factors. Platelet defects yield petechiae/purpura, whereas coagulation-factor deficiencies cause deep-tissue bleeds. Hemophilia A/B/C involve intrinsic-pathway factor deficits (VIII, IX, XI) with prolonged aPTT but normal platelet counts. Thrombocytopenia (platelets

Disseminated Intravascular Coagulation features systemic coagulation activation leading to simultaneous thrombosis and bleeding; common triggers include sepsis, trauma, malignancy, and obstetric events.

Critical Laboratory & Diagnostic Tools

Microscopic morphology (smear, biopsy) remains fundamental. Immunophenotyping by flow cytometry or immunohistochemistry confirms lineage and maturity. Cytogenetic studies (karyotype, FISH, PCR) identify translocations and mutations guiding diagnosis, prognosis, and targeted therapy.