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What is arthritis?

Arthritis is the inflammation of one or more joints. Classic symptoms of arthritis include joint pain, swelling, stiffness, and redness. However, there are over 100 types of arthritis with varying manifestations.

Arthritis may be due to gradual wear and tear on the joints or result from an autoimmune disorder. It may be triggered by injury (such as a fracture) or infection (viral, bacterial, or fungal). A person may have more than one type of arthritis.

Arthritis affects both sexes and all ethnicities. Most types are more common in adults, but arthritis can occur at any age and can affect joints in many different parts of the body. Some specific types of arthritis include:

  • Osteoarthritis (OA) – the most common form of arthritis, affecting about 27 million people in the United States; it is chronic and results from the breakdown of cartilage in the joints; associated with the aging process and "wear and tear"
  • Rheumatoid arthritis (RA) – an autoimmune disorder that affects about 1.3 million people in the U.S.; nearly 3 times more women than men are affected by RA
  • Juvenile rheumatoid arthritis (JRA) – also called juvenile idiopathic arthritis (JIA); the most common type of childhood arthritis; involves at least 6 weeks of persistent arthritis in a child younger than 16 years of age
  • Gout – associated with excess uric acid that deposits needle-like crystals into affected joints, especially in the big toe, causing sudden and severe pain; most commonly affects men over the age of 30
  • Psoriatic arthritis – associated with the skin condition psoriasis; characterized by joint pain, stiffness and swelling in any part of the body
  • Septic arthritis – caused by an infection in a joint; it can result in serious joint damage in a short period of time if not treated promptly
  • Ankylosing spondylitis – a chronic form of arthritis that mainly affects the spine
  • Reactive arthritis – a form of arthritis that affects typically the knees, ankles, and feet and is also associated with inflammation of the urethra and the eyes (conjunctivitis or uveitis); it is so called because it normally occurs as a reaction to an infection somewhere in the body.

Some organizations classify fibromyalgia, Sjogren syndrome, scleroderma, and lupus (SLE) as types of arthritis as well.

Laboratory tests can be useful in diagnosing these forms of arthritis and/or ruling out other conditions that may cause similar symptoms. For more detailed information on these, click on the linked condition name to go to that article.

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