Arthritis includes more than 100 diseases that damage joints. Degeneration or inflammation of joints, which enable the body to move, can cause pain, swelling, deformity and eventual disability. Some forms of arthritis also injure other parts of the body, such as the skin, eyes, urinary tract or heart.

More than 46 million Americans, including over one-fifth of adults, have some form of arthritis, according to the Centers for Disease Control and Prevention (CDC). The majority of these individuals have osteoarthritis (OA), which involves degeneration of cartilage, usually due to gradual wear and tear related to aging.

Some forms of arthritis, including rheumatoid arthritis (RA), are autoimmune diseases, meaning the body's immune system mistakenly attacks healthy tissues. RA is a debilitating disease in which inflammation causes pain and eventually deforms joints. It can affect people of all ages. Juvenile rheumatoid arthritis is the most common form of arthritis in children.

Other arthritic conditions include:

• Gout and pseudogout, in which crystals form in joints
  
• Psoriatic arthritis, the joint pain and swelling that affect some people who have the skin disease psoriasis
  
• Reiter's syndrome, a reaction to an infection
  
• Ankylosing spondylitis, which mainly affects the spine
  
  

Diagnosis of arthritis involves a physical examination, medical history, imaging tests such as x-rays or ultrasound, and sometimes blood or urine tests.

Arthritis is generally a chronic condition that cannot be cured. Some forms have periods of flare-ups and remission. Treatment plans focus on alleviating pain, preventing further degeneration and maintaining or improving joint mobility. Common treatments include exercises, physical therapy, occupational therapy and medications. In severe cases, surgery may be performed to remove growths or replace a joint (arthroplasty).

Some forms of arthritis may be prevented by avoiding infection or injury. Practices that minimize stress on joints, such as regular exercise and maintaining a healthy weight, may help avert or delay the onset of arthritis. Clinical studies are under way to determine the effectiveness of additional treatments for arthritic pain.