The Diseases of Hematopoietic and Lymphoid Systems

Disorders of the hematopoietic and lymphoid systems include a variety of different diseases that are classified as disorders primarily affecting red cells, white cells, and the hemostatic system. Diseases of red cells, white cells, and the hemostatic system include anemia, leukopenia, and thrombocytopenia. On the contrary, proliferation may be reactive, such as in reactive lymphadenitis, leukocytosis, and thrombocytosis, or neoplastic, such as in leukemias and malignant lymphomas. The hematopoietic and lymphoid systems, unlike other organ systems, are not confined to a single anatomic site. Therefore, when considering diseases of the hematopoietic and lymphoid systems, it is important to keep in mind that hematopoietic and lymphoid cells are spread throughout the body. Therefore, a patient with lymphoma diagnosed by lymph node biopsy can also have neoplastic lymphocytes in the bone marrow and blood. Neoplastic lymphoid cells in the bone marrow can inhibit hematopoiesis, leading to cytopenias, and the further spread of malignant cells to the spleen and liver may cause splenomegaly and hepatomegaly. Thus, in benign and malignant hematolymphoid disorders, a single underlying abnormality can result in various systemic manifestations. In this chapter, we first briefly introduce the structure and function of hematopoietic and lymphoid systems, describe some non-neoplastic conditions, and then mainly focus on white cell disorders.