Causes and Types of Gout

Gout is a form of arthritis characterized by high levels of uric acid (one of the body's waste products) in the blood and crystals in the joints. These crystals irritate the joints and surrounding tissue. The crystals trigger an inflammatory response and the affected joint becomes red, warm, swollen and extremely painful. Most commonly, the first attack is in the joint of the big toe. Other vulnerable sites include the knee, wrist, heel, instep and Achilles tendon.

The initial attack may resolve on its own within a few days. Subsequent attacks often require treatment. If neglected, the condition may eventually affect other joints. Repeated attacks generally strike without warning and occur with increasing frequency. They may eventually erode bone and cause permanent loss of mobility and joint deformity.

Gout affects about 2.1 million Americans. The disorder occurs much more frequently in men, most often starting after age 30. In women, attacks of gout usually don't begin until after menopause. Obesity increases the risk of developing gout; about half of patients with gout are 15 percent or more above ideal weight.

Normally, your body processes uric acid and excretes it with urine. Gout occurs when there is an excessive formation of uric acid, or when your kidneys are not functioning properly and cannot eliminate it.

Two Types of Gout

 Primary gout, which is inherited, results from an increased production of uric acid, a reduced excretion of uric acid in the urine, or some combination of the two. In secondary gout, high uric acid levels are caused by certain medications, such as diuretics, chronic kidney failure, or a massive release of the chemical precursors of uric acid that occurs during the rapid destruction of cells (for instance, during cancer chemotherapy).

Gouty Arthritis

Acute gouty arthritis is initiated by the deposition of sodium urate crystals into a joint and its synovial membrane. White blood cells (specifically, polymorphonuclear cells) enter the joint, engulf the urate crystals, and release a number of substances that trigger inflammation and an acute attack of arthritis. Urate crystals can also accumulate in many other sites, such as the kidneys, tendons, bones and subcutaneous tissues. Accumulations of urate create characteristic lesions called tophi, uric acid crystals surrounded by cells that have massed to defend against the deposited "foreign body."

Chronic gouty arthritis results when a joint is damaged by the formation of tophi within and around the joint. Osteoarthritis often complicates chronic gout.

A high blood level of uric acid (hyperuricemia) is a consistent finding in patients with gout, but many people with persistent hyperuricemia never develop gout. In some cases, urate crystals build up for 10 to 20 years before the first episode of gout strikes. In addition, it appears that a rapid drop (as well as a rapid rise) in blood uric acid levels can precipitate attacks of acute gout.

Last Updated: 6/8/2003
The Johns Hopkins University 1996-2003.  All rights reserved.  This information is not intended to provide advice on personal medical matters, nor is it intended to be a substitute for consultation.