DECT Useful in Suspected Gout With Negative Joint Aspiration

Alice Goodman

November 10, 2011

November 10, 2011 (Chicago, Illinois) — Dual-energy computed tomography (DECT), commonly used by urologists to differentiate between uric acid- and calcium-based kidney stones, can also be used to identify gout in patients suspected of having the disease but in whom results of fluid aspiration tests have been negative.

A study presented here at the American College of Rheumatology (ACR) 2011 Annual Meeting confirmed the sensitivity and specificity of DECT in diagnosing gout as well as identifying which patients should have this test.

"We don't see DECT as replacing the standard test, but we do use it as a routine clinical tool to confirm the suspicion of gout in selected patients in whom we suspect gout but can't diagnose it and have exhausted current technology," said lead author Tim Bongartz, MD, consultant in rheumatology at the Mayo Clinic in Rochester, Minnesota.

The study was conducted in 2 parts. In part 1, investigators enrolled 40 patients with confirmed gout on the basis of the presence of crystals in their joint aspiration fluid and 40 patients with other joint disease and negative findings on fluid aspiration. All patients underwent DECT.

In the 40 patients with confirmed gout, the Mayo Clinic team identified 35 true-positive and 5 false-positive results with DECT. All the patients with false-positive results on DECT had a short disease duration (<6 weeks). In the 40 patients without a diagnosis of gout on joint aspiration, 34 were found to be true-negative and 6 were found to be false-positive. All of those cases involved the knee joint.

"DECT was sensitive and specific, but was more useful in patients with a long duration of disease. The resolution of the scan is about 0.3 mm, so the crystals need to be a certain size to be detected by the scan. These findings also tell us to be alert to false-positive imaging at the knee," he stated.

Part 2 of the study included 30 patients with a clinical suspicion of gout and at least 1 clinical feature or lab finding associated with gout, but who had had a negative joint aspiration. In this group, 16 had a negative DECT scan and 14 had a positive DECT scan. Two of these 14 patients dropped out of the study, and 11 were positive for gout on confirmatory aspiration of the area identified on DECT scan (not always the joint space; some were around the tendons).

"Not every patient should have DECT. We don't want our patients to have to pay for our pretty pictures [if they are not necessary]. This study tells us to use DECT in patients with negative routine tests or in whom aspiration is contraindicated, such as a patient with a big red swollen toe that may be infected and shouldn’t have needles in that tissue. Identifying gout results in lifelong therapy, so it is important to diagnose gout. The danger of DECT is overuse of technology," he emphasized.

"This technology is exciting. We know a lot of patients have gout, but you can't always see the crystals in the aspirated fluid even though you are sure it's gout. DECT will show the presence of gout even if the aspirate is negative. The caveat is that it only identifies longer-standing gout that is clinically silent," said Eric Matteson, MD, chair of the Division of Rheumatology at the Mayo Clinic in Rochester, Minnesota, and chair of the ACR Communication and Marketing Committee. Dr. Matteson was not involved in the study.

DECT is useful in finding crystals that collect around ligaments and tendons, where fluid cannot be collected for aspiration, he continued. "You may not be able to go after the right areas with aspiration, but you can go to these areas with DECT," he stated.

Dr. Bongartz and Dr. Matteson have disclosed no relevant financial relationships.

American College of Rheumatology 2011 Annual Meeting; Abstract #1617. Presented November 7, 2011.