Lymph nodes are dilated portions of the lymphatic system where lymphatic fluid (lymph) is filtered. The fluid is drained from interstitial spaces and carried by afferent lymphatic vessels to the lymph nodes. It contains the excess tissue fluid that is not drained out of the tissue spaces into the venules and veins and may contain large particles and proteins that cannot enter these vessels. Efferent lymphatic vessels then carry the filtered lymph out of the nodes and eventually drains it into the venous circulation (bloodstream). If the lymph nodes did not filter the lymphatic fluid, debris and microorganisms may enter the bloodstream where it can disturb blood flow or lead to systemic infections. Lymph nodes can become diseased and enlarged for various reasons and this is known as lymphadenopathy. Inflammation of the lymph node is specifically known as lymphadenitis.
What is lymphadenitis?
Lymphadenitis is the term for inflammation of the lymph nodes. Due to the inflammatory process the node is usually enlarged. The term lymphadenopathy commonly refers to enlargement of the node and can be applied to any disease of the lymph node. Lymphadenopathy does not specifically indicate inflammation of the node as is the case with the term lymphadenitis. However, the term lymphadenopathy is more commonly used and the distinction is rarely made.
There are about 600 lymph nodes, also referred to as lymph glands, in the human body. It plays a vital role in fighting off infection and removing large particles of cellular debris from the circulation. In order to do this, lymphocytes (a type of white blood cell) are concentrated in the lymph nodes awaiting any invading pathogens. When the lymphocytes are exposed to an infection, it produces antibodies against the invader proteins. This allows the lymphocytes to exit the node and target the site of infection. Other immune cells are also recruited to the lymph node at the time of an infection. This ensures that any pathogens that are at a specific site and escape the immune response at the site will be neutralized in the lymph node before reaching the circulation.
Picture from Wikimedia Commons
Causes of Lymphadenitis
Most cases are due to an infection – bacterial, viral or fungal. With infections the lymph nodes are typically firm and tender although it may feel very hard with abscess formation. It is usually one-sided in acute infections, particularly bacterial infections. Regional lymph nodes are more frequently involved but in systemic infections, particularly with viral infections, the inflammation and swelling can affect nodes throughout the body. The major groups of lymphs in the neck, armpits and groin may be enlarged even with a localized infection. In these cases the swelling of the lymph nodes are enlarged but not tender.
Lymphadenitis can occur in the nearby lymph nodes at a site of intense inflammation even if it arises due to non-infectious causes. The inflammatory mediators may enter the lymphatic system and trigger inflammation within the lymph node either directly or by activating white blood cells in the lymph node. Inflammation may be due to the presence of a foreign body or severe trauma to an area.
The presence of malignant cells (cancer cells) in the lymph node may also cause lymphadenitis. It typically causes hard enlargement of the lymph nodes. These lymph nodes may be painful even without pressure applied to it or can even be painless. It is more likely to occur with malignancies affecting the white blood cells and bone marrow like leukemia.
Lymphoma is a primary lymph node cancer involving the lymphocytes. It tends to present as a hard painless swelling of the lymph nodes. Non-Hodgkin’s lymphoma is the more common type of lymphoma. Lymph node involvement in cancer affecting a specific organ may be an indication of metastasis meaning that the cancer could be spreading to other sites.
Normally the immune system is triggered by invading pathogens, however, in certain immunologic disorders the immune activity is directed at the body’s tissues. There is no infection but the body’s immune system is activated and aggressively attacking normal and healthy tissue. This may be seen in conditions like rheumatoid arthritis, when certain medication or foreign substances are injected into the bloodstream (serum sickness) or genetically dissimilar cells to that of the host (graft versus host disease).
- Immunodeficiency like with AIDS (acquired immunodeficiency syndrome).
- Blood diseases like sickle cell anemia and thalassemia.
- Drugs like mesantoin.
Signs and Symptoms
Swelling of the lymph node is the main presenting feature. It is usually tender or even painful. A palpable mass (lump) may be detected under the skin. At times the inflammation can involve the tissue around the lymph node. The overlying skin is typically red and warm to touch. If the lymphatic vessels are involved (lymphangitis) then there may be red streaks on the skin corresponding to the course of the vessel. Fever, chills, malaise and loss of appetite may be associated with the underlying cause of lymphadenitis.