Ross & Wilson Anatomy and Physiology in Health and Illness (62 page)

describe the effects of the two main forms of lymphoma

explain why secondary disease of the lymph nodes is commonly found in individuals with cancer.

Lymphadenitis

Acute lymphadenitis (acute infection of lymph nodes) is usually caused by microbes transported in lymph from other areas of infection. The nodes become inflamed, enlarged and congested with blood, and chemotaxis attracts large numbers of phagocytes. If lymph node defences (phagocytes and antibody production) are overwhelmed, the infection can cause abscess formation within the node. Adjacent tissues may become involved, and infected materials transported through other nodes and into the blood.

Acute lymphadenitis is secondary to a number of conditions.

Infectious mononucleosis (glandular fever)

This is a highly contagious viral infection, usually of young adults, spread by direct contact. During the incubation period of 7 to 10 days, viruses multiply in the epithelial cells of the pharynx. They subsequently spread to cervical lymph nodes, then to lymphoid tissue throughout the body.

Clinical features include tonsillitis, lymphadenopathy and splenomegaly. A common complication is myalgic encephalitis (chronic fatigue syndrome,
p. 178
). Clinical or subclinical infection confers lifelong immunity.

Other diseases

Minor lymphadenitis accompanies many infections and indicates the mobilisation of normal protective mechanisms, e.g. proliferation of defence cells. More serious infection occurs in, e.g. measles, typhoid and cat-scratch fever, and wound or skin infections. Chronic lymphadenitis occurs following unresolved acute infections, in tuberculosis, syphilis and some low-grade infections.

Lymphomas

These are malignant tumours of lymphoid tissue and are classified as either Hodgkin’s or non-Hodgkin’s lymphomas.

Hodgkin’s disease

In this disease there is progressive, painless enlargement of lymph nodes throughout the body, as lymphoid tissue within them proliferates. The superficial lymph nodes in the neck are often the first to be noticed. The disease is malignant and the cause is unknown. The prognosis varies considerably but the pattern of spread is predictable because the disease spreads to adjacent nodes and to other tissues in a consistent way. The effectiveness of treatment depends largely on the stage of the disease at which it begins. The disease leads to reduced immunity, because lymphocyte function is depressed, and recurrent infection is therefore common. As lymph nodes enlarge, they may compress adjacent tissues and organs. Anaemia and changes in leukocyte numbers occur if the bone marrow is involved.

Non-Hodgkin’s lymphomas

These tumours, e.g.
multiple myeloma
and
Burkitt’s lymphoma
, may occur in any lymphoid tissue and in bone marrow. They are classified according to the type of cell involved and the degree of malignancy, i.e. low, intermediate or high grade. Low-grade tumours consist of well-differentiated cells and slow progress of the disease, death occurring after a period of years. High-grade lymphomas consist of poorly differentiated cells and rapid progress of the disease, death occurring in weeks or months. Some low- or intermediate-grade tumours change their status to high grade with increased rate of progress.

The expanding lymph nodes may compress adjacent tissues and organs. Immunological deficiency leads to increased incidence of infections, and if the bone marrow or spleen (or both) is involved there may be varying degrees of anaemia and leukopenia.

Malignant metastases

Metastatic tumours develop in lymph nodes in any part of the body. Lymph from a tumour may contain cancer cells that are filtered out by the lymph nodes. If not phagocytosed, they multiply, forming metastatic tumours. Nodes nearest the primary tumour are affected first but there may be further spread through the sequence of nodes, eventually reaching the bloodstream.

Disorders of the spleen

Learning outcome

After studying this section, you should be able to:

identify the main causes of splenomegaly.

Splenomegaly

This is enlargement of the spleen, and is usually secondary to other conditions, e.g. infections, circulatory disorders, blood diseases, malignant neoplasms.

Infections

The spleen may be infected by blood-borne microbes or by local spread of infection. The red pulp becomes congested with blood and there is an accumulation of phagocytes and plasma cells. Acute infections are rare.

Chronic infections

Some chronic non-pyogenic infections cause splenomegaly, but this is usually less severe than in the case of acute infections. The most commonly occurring primary infections include:

•
tuberculosis

•
typhoid fever

•
malaria

•
brucellosis (undulant fever)

•
infectious mononucleosis.

Circulatory disorders

Splenomegaly due to congestion of blood occurs when the flow of blood through the liver is impeded by, e.g., fibrosis in liver cirrhosis, or portal venous congestion in right-sided heart failure.

Blood disease

Splenomegaly may be caused by blood disorders. The spleen enlarges to deal with the extra workload associated with removing damaged, worn out and abnormal blood cells in, e.g., haemolytic and macrocytic anaemia, polycythaemia and chronic myeloid leukaemia (
Ch. 4
).

Splenomegaly may itself cause blood disorders. When the spleen is enlarged for any reason, especially in portal hypertension, excessive and premature haemolysis of red cells or phagocytosis of normal white cells and platelets leads to marked anaemia, leukopenia and thrombocytopenia.

Tumours

Benign and primary malignant tumours of the spleen are rare but blood-spread tumour fragments from elsewhere in the body may cause metastases. Splenomegaly caused by infiltration of malignant cells is characteristic of some conditions, especially chronic leukaemia, Hodgkin’s disease and non-Hodgkin’s lymphoma.

Diseases of the thymus gland

Learning outcome

After studying this section, you should be able to:

describe the principal disorders of the thymus gland.