Rheumatoid arthritis (RA) is traditionally considered a chronic, inflammatory autoimmune disorder that causes the immune system to attack the joints. It is a disabling and painful inflammatory condition, which can lead to substantial loss of mobility due to pain and joint destruction. RA is a systemic disease, often affecting extra-articular tissues throughout the body including the skin, blood vessels, heart, lungs, and muscles.
The name is derived from the Greek rheumatos meaning "flowing", the suffix -oid meaning "in the shape of", arthr meaning "joint" and the suffix -itis, a "condition involving inflammation".