Lymphedema is the buildup of fluid called lymph in the tissues under your skin when something blocks its normal flow. This causes swelling, most commonly in an arm or leg.
Lymph normally does an important job for your body. It carries foreign material and bacteria away from your skin and body tissues, and it circulates infection-fighting cells that are part of your immune system.
Lymph flows slowly through the network of vessels called your lymphatic system. Lymph flow stops at points along the way to be filtered through lymph nodes. Lymph nodes are small bean-shaped organs that are part of your immune system.
Lymph is formed from the fluid that surrounds cells in the body. It makes its way into very small lymphatic vessels. After traveling through these small vessels, lymph drains into deeper, wider lymph channels that run through the body. Eventually, lymph fluid returns to the blood.
Lymphedema occurs when there is inadequate lymph drainage from the body, usually from a blockage in a lymph channel. Lymphatic fluid builds up underneath the skin and causes swelling. Most commonly lymphedema affects the arms or legs.
Swelling from lymphedema can look similar to the more common edema caused by leakage from tiny blood vessels under the skin.
In most cases of lymphedema, the lymphatic system has been injured so that the flow of lymph is blocked either temporarily or permanently. This is called secondary lymphedema. Common causes include:
Surgical damage — Surgical cuts and the removal of lymph nodes can interfere with normal lymph flow. Sometimes, lymphedema appears immediately after surgery and goes away quickly. In other cases, lymphedema develops from one month to 15 years after a surgical procedure. Lymphedema occurs quite often in women who have had multiple lymph nodes removed during surgery for breast cancer.
An infection involving the lymphatic vessels — An infection that involves the lymphatic vessels can be severe enough to cause lymphedema. In areas of the tropics and subtropics, such as South American, the Caribbean, Africa, Asia and the South Pacific, parasites are a common cause of lymphedema. Filariasis, a parasitic worm infection, blocks the lymph channels and causes swelling and thickening below the skin, usually in the legs.
Cancer — Lymphoma, a cancer that starts in the lymph nodes, or other types of cancer that spread to the lymph nodes may block lymph vessels.
Radiation therapy for cancer — This treatment can cause scar tissue to develop and block the lymphatic vessels.
When lymphedema occurs without any known injury or infection, it is called primary lymphedema. Doctors diagnose three types of primary lymphedema according to when symptoms first appear:
At birth — Also known as congenital lymphedema. Risk is higher in female newborns. The legs are affected more often than the arms. Usually both legs are swollen.
After birth but before age 36 — Usually, it is first noted during the early teenage years. This is the most common type of primary lymphedema.
Age 36 and older — This is the rarest type of primary lymphedema.
All three types of primary lymphedema are probably related to the abnormal development of lymph channels before birth. The difference is when in life they first cause swelling of the legs or arms.