Rheumatoid arthritis (RA) differs from some other forms of arthritis because it is symmetrical, affecting both sides of the body.
Other types of arthritis, such as osteoarthritis, may affect only one side of the body. Rheumatoid arthritis is also characterized as an autoimmune disorder, one in which the body mistakenly attacks its own tissues, while osteoarthritis is a degenerative condition that happens over time.