Gout.
Last updated Wednesday, December 22, 2004
Figure 1 - Joint with gout versus a normal joint Causes and effectsWhat causes gout?
The pain and swelling of gout are caused by uric acid crystals that
deposit in the joint. Uric acid is a substance that normally forms when
the body breaks down waste products called purines. Uric acid usually
is dissolved in the blood and passes through the kidneys into the
urine. In people with gout, the uric acid level in the blood is so high
that uric acid crystals are deposited in joints and other tissues. This
causes the joint lining (the synovium) to become inflamed.
After several years, the uric acid crystals can build up in
the joint(s) and surrounding tissues. They form large deposits called
tophi that look like lumps just under the skin. Tophi often are found
in or near severely affected joints, on or near the elbow, over the
fingers and toes, and in the outer edge of the ear. If the tophi are
not prevented or treated, they can damage joints (see figure 1).
Uric acid crystals can form stones in the kidneys, in the
ureters (tubes connecting the kidneys and bladder), or in the bladder
itself. Several factors may cause the formation of these deposits. For
example, the deposits may be caused by not drinking enough liquids.
Because of this lack of fluid, the urine is unable to dissolve all the
uric acid. Deposits also may form as a result of metabolic
abnormalities, such as the body's inability to make urine-less acid. In
other instances, diet may be the culprit. With some people, a diet rich
in foods that further increases the production of uric acid may
increase their chances of developing kidney stones. If your doctor
suspects that diet is a contributing factor, you may be asked to
collect several urine samples. Tests then will be conducted to
determine the amount of uric acid your body produces. These tests are
particularly helpful because some people with gout produce and
eliminate a large amount of uric acid. These people may be more likely
to develop kidney stones. People with gout also may have high blood
pressure or kidney infections. Since these problems can cause kidney
damage, your doctor will check for signs of these problems and treat
them if they occur.
Almost all people with gout have too much uric acid in their
blood, a condition called hyperuricemia. However, there are many people
who have hyperuricemia but not gout. Hyperuricemia is caused by one or
both of the following:
- The kidneys can't get rid of uric acid fast enough.
- The body makes too much uric acid.
Hyperuricemia often is caused by using diuretic medications
("water pills"). Diuretics are used to get rid of excess body fluid and
to lower high blood pressure. However, diuretics can hamper the
kidneys' ability to remove uric acid, thus raising uric acid levels in
the blood.
Other factors, such as inherited traits and environmental factors (such as weight, alcohol use, and diet), also can play an important role in causing gout.
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