This is a systemic disorder, which means that it affects various organs of the body apart from the joints.
The inflammation starts in the lining of the joint (synovium) and eventually destroys the joint cartilage. In this condition the bones become soft. Rheumatoid arthritis affects many joints simultaneously, including the small joints of the hands. There are other variants of rheumatoid arthritis, but these are essentially similar in nature.
X-ray changes in RA are similar to osteoarthritis in terms of joint space narrowing but the pattern may be different. There is usually a loss of bone density.
Blood tests for rheumatoid arthritis are not very accurate.