Diagnosing Gout between Painful Episodes

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The summary below is from the full report titled "Synovial Fluid Analysis for Diagnosis of Intercritical Gout." It is in the 16 November 1999 issue of Annals of Internal Medicine (volume 131, pages 756-759). The authors are E. Pascual, E. Batlle-Gualda, A. Martínez, J. Rosas, and P. Vela.

What is the problem and what is known about it so far?

Gout is a type of arthritis that happens when uric acid crystals form in a joint. These crystals can form when blood levels of uric acid are high. The underlying cause of gout is unknown, but it tends to run in families. Any joint may be involved, but the joint where the big toe meets the foot is the most common site. During gout attacks, which tend to occur periodically, the joints become swollen, red, and painful. To diagnose gout, a physician puts a needle into the affected joint and removes some joint fluid (synovial fluid), then uses a microscope to look for uric acid crystals in this fluid. The diagnosis is more difficult if a person is not in the middle of a gout attack.

Why did the researchers do this particular study?

The researchers wanted to find out whether examination of the joint fluid could help to diagnose gout even when someone is not currently having an attack.

Who was studied?

The researchers studied 101 patients who had previously been diagnosed with gout, but whose last gout attack had stopped at least 2 months before the study.

How was the study done?

The researchers collected information on the study patients' history of gout, blood levels of uric acid, and anti-gout medications. They then inserted a small needle into each patient's big toe or knee joints to obtain samples of joint fluid. The joints studied had been involved in previous gout attacks. The researchers next examined this fluid under a microscope to look for gout crystals.

What did the researchers find?

The researchers could get fluid from 91 of the 101 joints (73 of 80 knees and 18 of 21 toes). The fluid contained crystals in all 43 patients who were not receiving anti-gout medicines but in only 34 of the 48 patients who were taking anti-gout medicines. The patients without crystals in the joint fluid had not had a gout attack for a longer period of time, had lower blood levels of uric acid, and were receiving anti-gout medicine for a longer time than patients who had crystals.

What were the limitations of the study?

The study is relatively small, so it had limited ability to identify specific factors that would be related to the absence of crystals in the joint.

What are the implications of the study?

Analysis of the joint fluid may be helpful in diagnosing gout during periods in which a patient has no swollen, painful joints.