Chapter 13: Diseases of White Blood Cells, Lymph Nodes, and Spleen

Learning Objectives

A bnormalities in white blood cells (WBCs) are nearly always quantitative (eg, too many or too few WBCs). These disorders may be neoplastic, as found in leukemia, or nonneoplastic. A qualitative or functional disorder of WBCs may accompany the quantitative disorder. Qualitative defects in WBC function with a normal WBC count occur, but they are uncommon. The approach to diagnosis of WBC disorders is shown in Figure 13–1.

Leukopenia

Description and Diagnosis

A low WBC count can occur because of a decreased number of lymphocytes, granulocytes, or both. A number of the immunodeficiency diseases are associated with a lymphocytopenia (see Chapter 3). Granulocytopenia primarily reflects a reduction in the number of neutrophils (neutropenia) in the peripheral blood. When the number of neutrophils decreases below about 1000 neutrophils/μL, the neutropenic patient becomes susceptible to infections. These illnesses range from mild to severe, depending on the type of organism and the effectiveness of the antibiotics used to treat it. A classification of granulocytopenic disorders follows.

Defects in the production of granulocytes may be caused by:

• Diseases associated with marrow failure, such as aplastic anemia.

• Diseases in which the marrow is infiltrated by leukemic cells or by metastatic cancer cells originating from another site; the decreased neutrophil production in this setting is typically associated with defects in the production of other blood cells as well.

• Suppression of granulocyte production by exposure to certain drugs; the list of drugs that can produce neutropenia is extensive; noteworthy examples are chemotherapeutic agents used in cancer treatment and certain nonsteroidal anti-inflammatory drugs (NSAIDs).

• Vitamin B₁₂ or folate deficiency; these disorders produce a megaloblastic anemia and defective DNA synthesis in granulocyte precursors.

• Suppression of granulocyte production by neoplastic cells, for example, large granular lymphocytic leukemia.

Accelerated removal of granulocytes may be caused by:

• Immunologically mediated injury to neutrophils following exposure to drugs, with the injury occurring from an immune response on the neutrophil surface.

• Immunologically mediated injury to neutrophils as part of an autoimmune disorder; for example, Felty syndrome is a variant of rheumatoid arthritis with neutropenia, splenomegaly, leg ulcers, and the joint lesions found in rheumatoid arthritis; the neutropenia can dominate the clinical course in patients with ...