Arthritis
Arthritis, itself a group of more than 100 different diseases, is one category of rheumatic diseases. Rheumatic diseases may cause pain, stiffness and swelling in the joints and other supporting body structures, such as muscles, tendons, ligaments, and bones. However, rheumatic diseases can affect other areas of the body, including internal organs. Some rheumatic diseases involve connective tissues (called connective tissue diseases), while others may be caused by an autoimmune disorder, which means the body's immune system attacks its own healthy cells and tissues.