rheumatoid arthritis

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A chronic disease marked by stiffness and inflammation of the joints, weakness, loss of mobility, and deformity.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun pathology A chronic and progressive disease in which the immune system attacks the joints. It is characterised by pain, inflammation and swelling of the joints, stiffness, weakness, loss of mobility and deformity. Tissues throughout the body can be affected, including the skin, blood vessels, heart, lungs, and muscles.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a chronic autoimmune disease with inflammation of the joints and marked deformities; something (possibly a virus) triggers an attack on the synovium by the immune system, which releases cytokines that stimulate an inflammatory reaction that can lead to the destruction of all components of the joint