Rheumatoid arthritis is a systemic chronic inflammatory disease that mainly affects the joints but can also impact other tissues and organs. It has unknown causes but is influenced by genetic and autoimmune factors. The disease causes severe changes in joints like the proximal interphalangeal and metacarpophalangeal joints and can also involve the skin, blood vessels, heart, lungs, and muscles. Common risk factors include female gender and advanced age, while clinical manifestations comprise pain, stiffness, swelling, and redness in the joints.