Disorders of the Lymphatic System and Lymphoid Tissue

(Fig. 12-6; 12-1)
Lymphangitis, which is inflammation of lymphatic vessels, usually begins in the region of an infected and neglected injury and can be seen as red streaks extending along an extremity. Such inflamed vessels are a sign that bacteria have spread into the lymphatic system. If the lymph nodes are not able to stop the infection, pathogens may enter the bloodstream, causing septicemia, or blood poisoning. Streptococci often are the invading organisms in such cases. In lymphadenitis, or inflammation of the lymph nodes, the nodes become enlarged and tender This condition reflects the body’s attempt to combat an infection. Cervical lymphadenitis occurs during measles, scarlet fever, septic sore throat, diphtheria, and, frequently, the common cold. Chronic lymphadenitis may be caused by the bacillus that causes tuberculosis. Infections of the upper extremities cause enlarged axillary nodes, as does cancer of the breast. Infections of the external genitals or the lower extremities may cause enlargement of the inguinal lymph nodes.

Edema is tissue swelling due to excess fluid. The condition has a variety of causes, but edema due to obstruction of lymph flow is called lymphedema. Possible causes of lymphedema include infection of the lymphatic vessels, a malignant growth that obstructs lymph flow, or loss of lymphatic vessels and nodes as a result of injury or surgery. Areas affected by lymphedema are more prone to infection because the filtering activity of the lymphatic system is diminished. Mechanical methods to improve drainage and drugs to promote water loss are possible treatments for lymphedema, elephantiasis is a great enlargement of the lower extremities resulting from lymphatic vessel blockage by small worms called filariae. These tiny parasites, carried by insects such as flies and mosquitoes, invade the tissues as embryos or immature forms. They then grow in the lymph channels and obstruct lymphatic flow. The swelling of the legs or, as sometimes happens in men, the scrotum, may be so great that the victim becomes incapacitated. This disease is especially common in certain parts of Asia and in some of the Pacific islands. No cure is known.
The lymphatic system in relation to the cardiovascular system
Figure 12-1 The lymphatic system in relation to the cardiovascular system. Lymphatic vessels pick up fluid in the tissues and return it to the blood in vessels near the heart.
Location of lymphoid tissue
Figure 12-6 Location of lymphoid tissue.
Lymphadenopathy is a term meaning “disease of the lymph nodes.” Enlarged lymph nodes are a common symptom in a number of infectious and cancerous diseases. For example, generalized lymphadenopathy is an early sign of infection with human immunodeficiency virus (HIV), the virus that causes acquired immunodeficiency syndrome (AIDS). Infectious mononucleosis is an acute viral infection, the hallmark of which is a marked enlargement of the cervical lymph nodes. Mononucleosis is fairly common among college students. Enlarged lymph nodes are commonly referred to as glands, as in “swollen glands.” However, they do not produce secretions and are not glands.

Enlargement of the spleen, known as splenomegaly, accompanies certain acute infectious
diseases, including scarlet fever, typhus fever, typhoid fever, and syphilis. Many tropical parasitic diseases cause splenomegaly. A certain blood fluke (flatworm) that is fairly common among workers in Japan and other parts of Asia causes marked splenic enlargement. Splenic anemia is characterized by enlargement of the spleen, hemorrhages from the stomach, and fluid accumulation in the abdomen. In this and other similar diseases, splenectomy appears to constitute a cure.

Lymphoma is any tumor, benign or malignant, that occurs in lymphoid tissue. Two examples of malignant lymphoma are described next. Hodgkin disease is a chronic malignant disease of lymphoid tissue, especially the lymph nodes. The incidence of this disease rises in two age groups: in the early 20s among both men and women, and again after age 50, more commonly among men. The cause is unknown, but in some cases may involve a viral infection. Hodgkin disease appears as painless enlargement of a lymph node or close group of nodes, often in the neck, but also in the armpit, thorax, and groin. It may spread throughout the lymphatic system and eventually to other systems if not controlled by treatment. Early signs are weight loss, fever, night sweats, fatigue, anemia and decline in immune defenses.
A clear sign of the disease is the presence of Reed-Sternberg cells in lymph node biopsy tissue (Fig. 12-8). Chemotherapy and radiotherapy, either separately or in combination, have been used with good results, affording patients many years of life. Non-Hodgkin lymphoma is more common than Hodgkin disease. It appears mostly in older adults and patients with deficient immune systems, such as those with AIDS. Enlargement of the lymph nodes (lymphadenopathy), especially in the cervical (neck) region, is an early sign in many cases. It is more widespread through the lymphatic system than Hodgkin disease and spreads more readily to other tissues, such as the liver. Like Hodgkin disease, it may be related to a viral infection. It shares many of the same symptoms as are seen in Hodgkin disease, but there are no Reed-Sternberg cells on biopsy. The current cure rate with chemotherapy and radiation is approximately 50%.
Reed Sternberg cell characteristic of Hodgkin disease
Figure 12-8 Reed-Sternberg cell characteristic of Hodgkin disease. A typical cell has two nuclei with large, dark-staining nucleoli.
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