Regardless of cause, patients with HLH typically present with fever, splenomegaly, and pancytopenia. In severe cases, DIC and organ failure may supervene. An examination of the bone marrow shows macrophages phagocytosing red cells, platelets, and nucleated marrow cells. Laboratory abnormalities typically include a very high ferritin level (>10,000 µg/L), hypertriglyceridemia, high serum levels of soluble IL2 receptor, and low levels of circulating NK cells and cytotoxic T lymphocytes. In concert, these findings are quite sensitive and specific for HLH. Treatment varies depending on the underlying cause, but it is generally poor. In those with HLH stemming from inherited defects, hematopoietic stem cell transplantation offers a chance for cure.
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The most important disorders of white cells are neoplasms. Virtually all of these tumors are considered to be malignant, but they demonstrate a wide range of behaviors, ranging from some of the most aggressive cancers of man to tumors that are so indolent that they were only recognized recently as true neoplasms. Hematologic malignancies occur at all ages and include disorders that preferentially affect infants, children, and young adults, as well as the very old. As a group they are quite common; in aggregate, there are about 150,000 new hematologic malignancies diagnosed each year in the United States.
Current systems of classifying white cell neoplasms rely on a mixture of morphologic and molecular criteria, including lineage-specific protein markers and genetic findings. We will organize our discussion by dividing the white cell neoplasms into four broad categories based on the origin and differentiation state of the tumor cells, as follows:
Lymphoid neoplasms, which include certain leukemias and the non-Hodgkin and Hodgkin lymphomas. In many instances these tumors are composed of cells resembling some normal stage of lymphocyte differentiation, a feature that serves as one of the bases for their classification. A special group of lymphoid neoplasms are the plasma cell neoplasms and related entities, in which many of the clinical manifestations stem from abnormal immunoglobulins that are synthesized and secreted from the neoplastic cells.
Myeloid neoplasms, which include certain leukemias, myelodysplastic syndromes (MDSs), and myeloproliferative neoplasms. These tumors have in common an origin from a hematopoietic stem cell or some other very early hematopoietic progenitor, and they typically involve the bone marrow.
Histiocytic neoplasms, which include proliferative lesions of macrophages and dendritic cells. Of special interest is a spectrum of proliferations of Langerhans cells (Langerhans cell histiocytoses).
The numerous lymphoid neoplasms vary widely in their clinical presentation and behavior, and thus present challenges to students and clinicians alike. Some characteristically manifest as leukemias, with involvement of the bone marrow and the peripheral blood. Others tend to present as lymphomas, tumors that produce masses in lymph nodes or other tissues. Plasma cell tumors usually arise within the bones and manifest as discrete masses, causing systemic symptoms related to the production of a complete or partial monoclonal immunoglobulin. Although these tendencies are reflected in the names given to particular entities, in reality all lymphoid neoplasms have the potential to spread to lymph nodes and other tissues, especially the liver, spleen, bone marrow, and peripheral blood. Because of their overlapping clinical behavior, the diagnosis of lymphoid neoplasms is based on the morphologic and molecular characteristics of the tumor cells. Stated another way, for purposes of diagnosis and prognostication, it is most important to focus on what kind of cell the tumor is made up of, not where the tumor resides in the patient.