CT Scans Help Detect Gout When Aspirates Fail

A new study reveals that dual-energy computerized tomography (DECT) scans can detect gout in one-third of patients whose aspirates tested negative for the disease.

Researchers at the Mayo Clinic (Rochester, MN, USA) conducted a single-center study of 40 patients with active gout and 41 with other types of joint disease to examine the usefulness of DECT for detecting monosodium urate (MSU) deposits; the results were calculated against a combined reference standard (polarizing and electron microscopy of synovial fluid). To explore the diagnostic yield of DECT scanning, a third cohort was assembled consisting of patients with inflammatory arthritis and risk factors for gout who had negative synovial fluid polarizing microscopy results.

The results showed that the sensitivity of DECT for diagnosing gout was 0.90, while specificity stood at 0.83, with evidence of uric acid deposition found in 14 out of 30 patients (46.7%).The DECT scans worked particularly well in patients who had experienced several gout-like flares, but whose needle aspirates came back negative. After CT scans detected MSU deposits, ultrasound-guided aspirates were taken in those areas and tested for urate crystals. All false negative results were observed among patients with acute, recent-onset gout. All false positive results had advanced knee osteoarthritis (OA). The study was published on March 25, 2014, in Annals of the Rheumatic Diseases.

“The first flare of gout most commonly occurs in the big toe, but gout can affect pretty much every joint in the body, and the more gout flares you have the more likelihood that other joint areas will be affected,” said lead author rheumatologist Tim Bongartz, MD. “An accurate and early gout diagnosis is crucial because gout patients are treated with different medication than people with other forms of inflammatory arthritis, and proper medication and dietary changes can help prevent further gout attacks and the spread of the disease to other joints. The ability to visualize those deposits clearly broadens our perspective on gout.”

Gout is a medical condition usually characterized by recurrent attacks of acute inflammatory arthritis—a red, tender, hot, swollen joint. The metatarsal-phalangeal joint at the base of the big toe is the most commonly affected (approximately 50% of cases). However, it may also present as tophi, kidney stones, or urate nephropathy. It is caused by elevated levels of uric acid that crystallize and s deposit in joints, tendons, and surrounding tissues. The standard test for gout is by needle aspiration that draws fluid or tissue from an affected joint, which is then tested for the presence of uric acid crystals.

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