Chapter 24: Disorders of White Blood Cells and Lymphoid Tissues

Leukocytes originate from myeloid and lymphoid stem cells during hematopoiesis in the bone marrow, with their development regulated by various growth factors. Disorders of these cells include deficiencies like leukopenia, and more specifically neutropenia (a low neutrophil count), which critically compromises host defenses and can be congenital (such as Kostmann syndrome) or acquired (often due to drugs or infection). A common non-neoplastic condition is Infectious Mononucleosis, a self-limiting disorder typically caused by the Epstein–Barr virus (EBV) and marked by fever, lymphadenopathy, and the appearance of heterophile antibodies. The most significant pathologies are the Neoplastic Disorders, categorized into lymphomas and leukemias. Malignant Lymphomas are solid tumors arising from lymphoid tissue, primarily lymph nodes; these include diverse Non-Hodgkin Lymphomas (NHLs), which are multicentric and heterogeneous, and Hodgkin Lymphoma (HL), distinguished by the presence of unique Reed–Sternberg cells and a generally contiguous spread pattern. Leukemias are malignancies of hematopoietic precursor cells originating in the bone marrow, classified as acute or chronic based on cell maturity and progression speed. Acute leukemias (ALL and AML) involve rapidly proliferating immature blast cells, causing symptoms like anemia and bleeding due to bone marrow suppression, while chronic leukemias (CLL and CML) involve more differentiated cells, such as CML, which is frequently linked to the Philadelphia chromosome translocation. Finally, the chapter addresses Plasma Cell Dyscrasias, with Multiple Myeloma being a key malignancy of plasma cells characterized by destructive osteolytic bone lesions, hypercalcemia, and the pathological overproduction of monoclonal antibodies (M proteins or Bence Jones proteins).