Arthritis and rheumatism (ROO-mah-tism) are often used interchangeably. Arthritis is a term that implies damage or inflammation in one or more joints, while rheumatism is a general term that refers to any pain or ache originating from the muscles, joints, bones, or other parts of the musculoskeletal (muhsk-you-loh-SKEHL-ih-tal) system. Rheumatism is particularly referred to when there's no sign of a specific disease or arthritis. Many people suffer from rheumatic pains that vary from day to day and sometimes with the weather. Some patients report that their symptoms become worse when the weather is damp and cold. The most common type of arthritis is osteoarthritis (AH-stee-oh-are-THRYE-tiss), followed by rheumatoid arthritis and less common types of inflammatory arthritis. Osteoarthritis is a degenerative joint disease that largely affects cartilage, causing it to fray, wear, ulcerate, and in extreme cases, to disappear entirely, leaving a bone-on-bone joint. There's no known cause for rheumatoid arthritis, but it's believed to occur through a combination of genetic and environmental factors that trigger an abnormal immune response. Symptoms of rheumatoid arthritis include swelling, pain, stiffness, and the possible loss of function.