The American Academy of Family Physicians (AAFP) says lymphadenitis is an inflammation of the lymph nodes, which dot the network of lymphatic_vessels and provide a collecting area for the immune_system cells that defend against invaders. Lymphadenitis is not uncommon in children. Causes can include bacterial, viral or other infection. AAFP says people can develop an infection following a cat scratch or bite. Treatment depends on the specific cause of infection and its bacterium.