The lymphatic system is part of the immune system and functions to fight disease and infections. As infection-fighting cells and fluid accumulate, the lymph nodes enlarge to many times their normal size. Nearly all children will develop lymphadenopathy at some time, as the condition commonly occurs in response to an infection from a virus, such as an upper respiratory infection. Bacterial infections, such as strep throat caused by the streptococcus bacterium, can also cause lymphadenopathy.
Since enlarged lymph nodes are often near the source of infection, their location can help determine the cause. For example, an infant with a scalp infection may have enlarged lymph nodes at the back of the neck. Swollen lymph nodes around the jaw may be due to an infection in the teeth or mouth. However, the lymphadenopathy may be generalized, with lymph node enlargement in more than one area, which is typical of a viral illness.
Sometimes, the lymph nodes themselves can become inflamed and enlarged, a condition called lymphadenitis. Lymph nodes can also enlarge due to cancer in the lymphatic system, such as Hodgkin disease.