CT may fill gaps in gout detection

Dual-energy CT scanning (DECT) is effective in detecting monosodium urate (MSU) deposits, the crystalized form of uric acid in subjects with gout, and can aid clinical decision making when gout is suspected, according to a study presented Nov. 7 at the American College of Rheumatology annual scientific meeting in Chicago.

Patients who are suspected of having gout based on clinical presentation of symptoms may receive negative results from traditional tests such as polarizing microscopy of synovial fluid. Other patients may not be eligible for the test, which involves drawing fluid from joints.

Tim Bongartz, MD, a rheumatologist at the Mayo Clinic in Rochester, Minn., and colleagues sought to determine whether DECT scanning could be an effective alternative to the traditional tests.

Patients were divided into three groups: a control cohort of 40 subjects without any history of gout, a second cohort of 40 patients with active gout diagnosed with both polarizing and electron microscopy and a third cohort of 30 subjects who had a clinical suspicion for gout, but synovial fluid analysis was unavailable or negative for the presence of MSU crystals.

"We wanted to really challenge the new method by including patients who were only a few days into their first flare of gout," Bongartz said in a statement.

All participants underwent dual-source DECT scanning and images were classified by a musculoskeletal radiologist as positive or negative for MSU deposits. If positive, an ultrasound guided aspiration of the area was performed with subsequent polarizing microscopy to confirm findings.

The sensitivity and specificity of DECT for diagnosing gout was 93 percent and 95 percent, respectively. In the cohort consisting of patients with suspected gout, but negative synovial fluid aspiration, DECT imaging showed evidence of uric acid deposits in 46.7 percent of the patients. Ultrasound-guided aspiration confirmed the presences of MSU crystals in this group.

While Bongartz said the scans were “very accurate” overall, CT scans failed to identify 30 percent of cases in a subgroup of patients with very acute gout. CT scans are also significantly more expensive than the standard test for diagnosing gout, making DECT most useful in cases where joint fluid cannot be obtained or when fluid analysis comes back negative even though gout is strongly suspected.