What Is Arthritis?
Although the term literally means joint inflammation, arthritis really refers to a group of more than 100 rheumatic diseases and conditions that can cause pain, stiffness and swelling in the joints. Certain conditions may affect other parts of the body-such as the muscles, bones, and some internal organs-and can result in debilitating, and sometimes life-threatening, complications. If left undiagnosed and untreated, arthritis can cause irreversible damage to the joints.
The two most common forms of the disease, osteoarthritis and rheumatoid arthritis, have the greatest public health implications, according to the Arthritis Foundation. (For more on other causes of joint pain, see "Other Forms of Arthritis and Related Conditions.")
Osteoarthritis, previously known as "degenerative joint disease," results from the wear and tear of life. The pressure of gravity-the load of living-causes physical damage to the joints and surrounding tissues, leading to pain, tenderness, swelling, and decreased function. Initially, osteoarthritis is noninflammatory and its onset is subtle and gradual, usually involving one or only a few joints. The joints most often affected are the knee, hip and hand. Pain is the earliest symptom, usually made worse by repetitive use. Osteoarthritis affects 21 million people, and the risk of getting it increases with age. Other risk factors include joint trauma, obesity, and repetitive joint use.
Rheumatoid arthritis is an autoimmune disease that occurs when the body's own immune system mistakenly attacks the synovium (cell lining inside the joint). This chronic, potentially disabling disease causes pain, stiffness, swelling, and loss of function in the joints.
While the cause remains elusive, doctors suspect that genetic factors are important in rheumatoid arthritis. Recent studies have begun to tease out the genetic characteristics that can be passed from generation to generation. However, the inherited trait alone does not cause the illness. Researchers think this trait, along with some other unknown factor-probably in the environment-triggers the disease.
But rheumatoid arthritis can be difficult to diagnose early because it may begin gradually with subtle symptoms. According to the CDC, this form of arthritis affects more than 2 million people in the United States, and two to three times more women are affected than men.