Sjogren's syndrome is a chronic illness that sometimes accompanies rheumatic diseases, including rheumatoid arthritis and lupus. It is characterized by changes in the immune system that result in destruction of moisture-producing glands. The lack of moisture can affect many parts of the body, including the eyes, joints, lungs, mouth, and kidneys. Symptoms include coughing; dental cavities; difficulty chewing and/or swallowing; dry eyes, sometimes leading to damage to the cornea; dryness of the mouth, skin, throat, and all the mucous membranes; fatigue; hair loss; muscle weakness; and swollen salivary glands.

Kawasaki syndrome is an infectious disease that can cause symptoms of arthritis in children, accompanied by conjunctivitis; fever; a red rash on the body; a swollen, red tongue; and/or red or purplish-red discoloration and swelling palms of the hands and the soles of the feet. The cause of this disorder is not known. It primarily affects children under five years of age. Most children recover, but in some cases it causes permanent heart damage.

Chlamydia, the organism responsible for many cases of urethritis, has been linked to a form of arthritis that affects young women. In nearly half of the women with unexplained arthritis tested in one study, chlamydia was found in joints. Seventy-five percent had elevated levels of antibodies to chlamydia in their blood.