Rheumatoid arthritis is an autoimmune disorder that affects the joints and causes painful swelling, which can lead to bone erosion and joint deformity. According to the Mayo Clinic, rheumatoid arthritis is the result of a person's immune system attacking its own tissues.
The National Institute of Arthritis and Musculoskeletal and Skin Diseases reports that rheumatoid arthritis is frequently found in more than one joint, and it can affect any joint in the body. It can cause a sick feeling, including fatigue and sometimes a fever. Although anyone can get rheumatoid arthritis, it is more commonly found in women, often starting in middle age.