Porth's Essentials of Pathophysiology, 4e

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Disorders of White Blood Cells and Lymphoid Tissues

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normal size, and rupture of the spleen is an infrequent complication. In less than 1% of cases, mostly in the adult age group, complications of the central nervous system (CNS) develop. These complications include cra- nial nerve palsies, encephalitis, meningitis, transverse myelitis, and Guillain-Barré syndrome. The peripheral blood usually shows an increase in the number of leukocytes, with a white blood cell count between 12,000 and 18,000 cells/ μ L, 60% of which are lymphocytes. 14 The rise in white blood cells begins dur- ing the first week, continues during the second week of the infection, and then returns to normal around the fourth week. Although leukocytosis is common, leu- kopenia may be seen in some persons during the first 3 days of illness. Atypical lymphocytes are common, constituting more than 20% of the total lymphocyte count. Heterophil antibodies usually appear during the second or third week and decline after the acute illness has subsided. They may, however, be detectable for up to 9 months after onset of the disease. Most persons with infectious mononucleosis recover without incident. The acute phase of the illness usually lasts for 2 to 3 weeks, after which recovery occurs rap- idly. Some degree of debility and lethargy may persist for 2 to 3 months. Treatment is primarily symptomatic and supportive. It includes bed rest and analgesics such as acetaminophen and nonsteroidal anti-inflammatory drugs (NSAIDs) to relieve the fever, headache, and sore throat. Although splenic rupture is rare, avoidance of contact sports for a minimum of 3 weeks after diagnosis is recommended. 15 In persons with immunodeficiency disorders that lead to defects in cellular immunity (e.g., human immuno- deficiency virus [HIV] infection, immunosuppressant- treated recipients of organ or bone marrow transplants), EBV infection may contribute to the development of lymphoproliferative disorders (e.g., non-Hodgkin lym- phoma). 12 These persons have impaired T-cell immunity and are unable to control the proliferation of EBV- infected B cells.

Neoplastic Disorders of Hematopoietic and Lymphoid Origin The neoplastic disorders of hematopoietic and lymphoid origin represent the most important of the white blood cell disorders. They can be divided into two broad cat- egories based on the origin of the tumor cells: lymphoid neoplasms and myeloid neoplasms. The clinical features of these neoplasms are largely determined by their site of origin, the progenitor cell from which they originated, and the molecular events involved in their transforma- tion into a malignant neoplasm. Myeloid neoplasms arise from hematopoietic stem cells and normally give rise to monoclonal proliferations that replace normal bone marrow cells. They include the acute and chronic myelogenous leukemias. 4,7 The lym- phoid neoplasms encompass a group of entities that vary widely in their clinical presentation and behaviors. They include the B- and T-cell leukemias and lymphomas (non- Hodgkin and Hodgkin lymphomas) that originate in peripheral lymphoid structures such as the lymph nodes, where B and T lymphocytes undergo differentiation and proliferation. The plasma cell dyscrasias originate in the lymph nodes, where B cells differentiate into plasma cells. Leukemias The leukemias are malignant neoplasms of cells origi- nally derived from precursor myeloid or lymphoid tis- sue cells. The term leukemia (i.e., “white blood”) was first used by Rudolf Virchow to describe a reversal of the usual ratio of red blood cells to white blood cells. 16 syndrome, which is associated with severe bacterial infections.The acquired neutropenias encompass a wide spectrum of etiologies, including immunologically mediated bone marrow suppression, neutrophil injury and destruction, infection-related processes, and drug-induced mechanisms—particularly those related to cancer chemotherapeutic agents. ■■ Infectious mononucleosis is a self-limited lymphoproliferative disorder caused by the B-lymphotropic Epstein-Barr virus that is usually transmitted in the saliva.The disease is characterized by fever, sore throat, generalized lymphadenopathy, and the appearance of atypical lymphocytes and several antibodies in the blood, including the well-known heterophil antibodies commonly used in its diagnosis. Treatment is largely symptomatic and supportive and most people recover without incident.

SUMMARY CONCEPTS

■■ Neutropenia, which represents a marked reduction in neutrophils, can occur as a congenital or acquired disorder. Because the neutrophil is essential to host defenses against bacterial and fungal infections, severe and often life-threatening infections are common in persons with neutropenia. ■■ Congenital neutropenia consists primarily of cyclic neutropenia, which is characterized by cyclic oscillations of peripheral neutrophils, and severe congenital neutropenia or Kostmann