The lymphatic system is characterized by a complex and extensive network of lymph vessels which is responsible for the transport of lymph fluid (containing compounds such as proteins and lipids) to and from tissues. During its transport, the fluid is filtered by the lymph nodes – these contain residential lymphocytes. In this way, the lymphatic system is an integral part of the body’s immunity.

When there is a blockage in the lymph vessels the lymph fluid is not effectively returned to the bloodstream and this can result in localized swelling i.e. lymphedema. This swelling may occur in numerous locations - not only the legs and arms but also in the head, neck, breast, trunk or genitals.

Stages

Lymphedema is further categorized according to its stage:

Stage 0 (subclinical or latent)

This stage can be present for months or years however, symptoms are not common. Swelling is not visible yet however the lymphatic system has undergone damage. 

Stage I (mild)

Visible swelling has begun and the skin indents when it is pressed but there is no visible evidence of scarring. Elevating the affected limb can temporary reduce the swelling until the limb is returned to its normal position.

Stage II (moderate)

The swelling increases and elevation does not decrease swelling. The skin does not indent but becomes firm due to scarring (fibrosis).

Stage III (severe, lymphostatic elephantiasis)

The skin becomes very swollen, the affected body part has swollen in size and volume, and the skin has changed texture.

Types of lymphedema:

Primary lymphedema

There are three types of this rare and hereditary form of lymphedema which occur when there is a physiological deformation of the lymphatic system. Unfortunately, family history of lymphedema is not a necessity for its development in a person.

• Congenital lymphedema (or Milro disease) – this is an inherited form of lymphedema which appears to be associated with a failure in the lymphatic system. It is present from birth but may occur at any point up to the age of one year old. This form represents approximately 20-25% cases of primary lymphedema.
• Lymphedema praecox (or Meige disease) – this constitutes 65-80% cases of primary lymphedema. The symptoms most commonly become apparent during puberty. The higher incidence in females may suggest an association between pathogenesis and estrogen.
• Late Onset lymphedema (or lymphedema tarda) – this form occurs following 35 years of age but only accounts for approximately 10% of primary lymphedema cases.

Secondary lymphedema

Secondary lymphedema occurs when there is damage or blockage in an otherwise healthy lymphatic system. The hampered functioning of the lymph system removes an essential component of a person’s immunity, thereby making it more difficult for the body to fight infections.

Worldwide, filariasis is the largest contributing factor of the disease – it is a parasitic infection spread among humans via mosquitoes carrying the parasite Wuchereria bancrofti. It causes damage to the lymph system which eventually results in the characteristic swelling of lymphedema.

Malignant cancer and its treatment by surgery is also a very common cause of secondary lymphedema. This is because it involves the removal of regional lymph nodes or lymph vessels which can damage the lymph nodes and lymph vessels. In the same way damage due to burns and radiation can increase the likelihood of this form of lymphedema.

References:

• http://www.medicinenet.com/lymphedema/article.htm#what_is_lymphedema
• http://www.mayoclinic.org/diseases-conditions/lymphedema/basics/definition/con-20025603
• http://www.lymphnet.org/le-faqs/what-is-lymphedema
• https://www.nlm.nih.gov/medlineplus/lymphedema.html
• http://emedicine.medscape.com/article/1087313-overview#showall
• http://www.cancer.net/navigating-cancer-care/side-effects/lymphedema
• http://www.breastcancer.org/treatment/lymphedema/how/stages
• http://www.lymphnotes.com/article.php/id/474/
• http://www.cancerresearchuk.org/about-cancer/what-is-cancer/body-systems-and-cancer/the-lymphatic-system-and-cancer