The main involvement of lymph vessels are in relation to:

	the spread of disease in the body
	the effects of lymphatic obstruction.

Spread of disease

The materials most commonly spread via the lymph vessels from their original site to the circulating blood are fragments of tumours and infected material.

Fragments of tumours : Tumour cells may enter a lymph capillary draining a tumour, or a larger vessel when a tumour has eroded its wall. Cells from a malignant tumour, if not phagocytosed, settle and multiply in the first lymph node they encounter. Later there may be further spread to other lymph nodes, to the blood and to other parts of the body via the blood. In this sequence of events, each new metastatic tumour becomes a source of malignant cells that may spread by the same routes.

Infected material : Infected material may enter lymph vessels either at their origin in the interstitial spaces, or through the walls of larger vessels invaded by microbes when infection spreads locally . If phagocytosis is not effective the infection may spread from node to node, and eventually reach the blood stream.

Lymphangitis (infection of lymph vessel walls) : This occurs in some acute pyogenic infections in which the microbes in the lymph draining from the area infect and spread along the walls of lymph vessels, e.g. in acute Streptococcus pyogenes infection of the hand, a red line may be seen extending from the hand to the axilla. This is caused by an inflamed superficial lymph vessel and adjacent tissues. The infection may he stopped at the first lymph node or spread through the lymph drainage network to the blood.

Lymphatic obstruction

When a lymph vessel is obstructed there is an accumulation of lymph distal to the obstruction called lymphoedema. The amount of resultant swelling and the size of the area affected depend on the size of the vessel involved. Lymphoedema usually leads to low-grade inflammation and fibrosis of the lymph vessel and further lymphoedema are complications which only occur if the blockage is severe and the swelling is prolonged. The most common causes in the UK are tumours and surgery.

Tumours : A tumour may grow into, and include, a lymph vessel or node, and obstruct the flow of lymph. A large tumour outside the lymphatic system may cause sufficient pressure to stop the flow of lymph.

In other parts of the world parasitic infections can be a cause of severe forms of lymphoedema. Filariasis is an example of this and it is common in Africa resulting in the condition known as elephantiasis. This is caused by parasitic infection by a nematode worm which inhabit the lymphatics causing blockage and is transmitted to humans via mosquitoes.

Surgery : In some surgical procedures lymph nodes are removed because cancer cells may have already spread to them. This is done to prevent growth of secondary tumours and further spread via the lymphatic system. e.g. removal of the axillary nodes in mastectomy.

Enlarged lymph nodes : Lymph nodes become enlarged, (lymphadenopathy), when their work load is increased by infection. They usually return to normal when the infection subsides but if there is chronic infection or repeated acute episodes they may become fibrosed and remain enlarged. Other causes include tumours (lymphomas) and excess abnormal material in lymph, especially if present for a long time, e.g. coal dust from the lungs, necrotic material from a tumour.

Lymphadenitis : Acute lymphadenitis 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 When phagocytic and antibody activity are not effective the infection may lead to: · abscess formation in the node · infection of adjacent tissues · a spread of infected material to other nodes and then to the blood, causing septicaemia or bacteraemia .

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 nodes then to lymphatic tissue throughout the body. Clinical features include tonsilitis, lymphadenopathy and splenomegaly. A common complication is chronic fatigue syndrome. Clinical or subclinical infection confers lifelong immunity.

Other diseases connected with lymphadenitis :

Minor lymphadenitis accompanies many infections and indicates the mobilisation of normal protective resources.

More serious infection occurs in:

measles, anthrax, typhoid fever, wound and skin infections, cat-scratch fever, lymphogranuloma venereum, and bubonic plague.

Chronic lymphadenitis occurs following unresolved acute infections, in tuberculosis, syphilis and some low-grade infections.

Lymphomas

These are malignant tumours of lymphoid tissue that are classified as Hodgkin's lymphomas or non-Hodgkins lymphomas. Briefly in these diseases there is progressive painless enlargement of lymph nodes throughout the body, often noticed first in the neck. The disease is malignant and the cause is unknown. The rate of progress varies considerably but the pattern of spread is predictable. The effectiveness of treatment depends largely on the stage of the disease at which it begins. Complications include deficiency of cell-mediated immunity, and pressure on other organs from the swollen lymph nodes.