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LYMPHOEDEMA
This is defined as the excessive accumulation of interstitial fluid as a result of defective lymphatic drainage. The condition may be further subdivided into primary and secondary lymphoedema, secondary lymphoedema being the most common. Primary lymphoedema is three times more common in women than in men and has no known cause; secondary lymphoedema is the result of some recognized pathological process disrupting the lymphatic drainage.
Further subdivisions of primary lymphoedema have been made on the basis of the anatomical lymphatic abnormalities that are present. The lymphatic channels may be absent or severely hypoplastic, being few in number and petering out more proximally. They may also be excessive in number, though defective in function: such lymphatic hyperplasia is usually associated with excessive numbers of lymph nodes. The lymphatics may be dilated and ectatic (megalymphatics) and this abnormality is often associated with chylous ascites, chylothorax, and lymphatic reflux. Finally the lymphatics may be obstructed  in primary lymphoedema this is often associated with fibrosis within the lymph nodes.
Secondary lymphoedema
All patients presenting with lymphoedema must have a possible ‘cause’, excluded by careful examination and special tests where necessary.
Filariasis
This helminthic infection is a major global cause of lymphoedema. It is endemic in parts of Africa, especially the west coast, and is also common in India and parts of South America. The worm enters the lymphatics and lodges in the lymph nodes, where a severe fibrotic reaction causes obstruction to the lymphatic pathways, which are often grossly dilated This results in severe swelling of the limbs (usually the lower) called elephantiasis.
The diagnosis is confirmed by finding microfilariae, which enter the blood in large numbers at night. To provide the maximum possibility of detecting filariae, a blood sample should be taken at midnight. A strongly positive complement fixation test suggests active or past filariasis.
Treatment with diethylcarbamazine destroys the filariae but does not reverse established lymphoedema; progression of the disease may, however, be slowed or prevented. Established lymphoedema is treated by the same methods as those used to treat primary lymphoedema. 
Malignancy
Any malignant process that spreads to the lymph nodes can cause secondary lymphoedema, but this is more common after surgical resection or radiotherapy directed against nodal deposits of tumour. Hodgkin's disease and the non-Hodgkin's lymphomas can present with lymphoedema; this may also occur in patients with malignant melanomas and testicular seminomas.
Surgical block dissection
This operation is invariably carried out to treat malignancies affecting lymph nodes, although in many cases it forms part of a staging or prophylactic procedure. The carcinomas commonly requiring block dissections are those of the breast and uterus. Malignant melanoma and testicular tumours are also often treated by block dissection or irradiation. 
Radiotherapy
Radiotherapy is a common cause of secondary lymphoedema of the upper limb in patients with breast carcinoma, especially when surgical block dissection has also been performed. Such combination therapy carries a higher risk of lymphoedema than either treatment in isolation. Radiotherapy results in nodal fibrosis, which can also cause obstruction of the lymphatic vessels. Recurrent tumour in an irradiated field may be responsible for lymphoedema developing some years after treatment of the primary disease.
Trauma
Severe trauma occasionally causes loss of tissue which includes lymph nodes or lymphatic channels. This is particularly seen after severe degloving injuries.
Chronic infection
Although tuberculosis has often been cited as a cause of lymphoedema, it is uncommon.
Chronic inflammation
At the St Thomas' lymphoedema clinic one or two patients are seen every year with severe rheumatoid disease or severe chronic eczema who develop mild lymphoedema. Chronic stimulation of the lymph nodes in these patients results in fibrosis and mild obstruction to the lymphatic drainage.
Acute infection
Severe cellulitis can occasionally damage the local subcutaneous lymphatics and cause mild lymphoedema. Patients suffering from subclinical primary lymphoedema may also develop a secondary cellulitis: the two presentations can be difficult to distinguish.
Self-induced
This quite common form of Munchausen's syndrome is produced by repeated tight application of a tourniquet. Total disuse of a limb can also cause swelling: this form of self-induced lymphoedema should be suspected if the limb cannot be moved passively. Lymphograms are usually normal or only mildly unusual. The cause should be suspected if there is a sharp cut-off to the lymphoedema and a rut due to application of the tourniquet. Patients should be told of the doctor's suspicions and referred for psychiatric advice.
Primary lymphoedema
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