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Gout: Two New Studies Show Benefits of DECT and Ultrasound for Diagnosis and Monitoring

February 26, 2021
Researchers evaluate the effectiveness of DECT and ultrasound in comparison to SFA for gout diagnosis.

with Jasvinder Singh, MD

Traditional methods of diagnosing gout have been enhanced in recent years by imaging techniques such as ultrasound and DECT (dual-energy computed tomography). The 2018 EULAR recommendations for the diagnosis of gout support the use of these imaging techniques, in “patients with atypical clinical features and in whom crystal identification is not feasible.”1 The question is how well these methods compare to traditional detection methods involving monosodium urate (MSU) crystals in synovial fluid analysis (SFA).

Data comparing the effectiveness of the various modalities have been sparse, with studies typically having small sample sizes, retrospective design, and using slightly different standards of comparison. Prior studies were also generally made up of patients with longstanding, established gout, making them less useful for analyzing the effectiveness of the techniques for diagnosing the disease.2

Now a new study compares DECT and ultrasound methods to the traditional approach and offers some clarity for clinicians on the use of DECT and/or ultrasound for diagnosis. In addition, a separate paper by an international working group of rheumatologists offers some insight into the use of ultrasound in the monitoring of gout in patients with chronic disease. 

Could DECT and ultrasound –­ or both together – better diagnose of gout compared to SFA? (Image: iStock)

 

Gout Diagnosis: DECT, Ultrasound, or Both?

The first study, published in January 2021, in Rheumatology, aimed to evaluate the accuracy of DECT and ultrasound –­ or both together – in the diagnosis of gout and measured those methods against the gold standard (SFA).2 The prospective cohort analysis looked at patients from a single outpatient rheumatology clinic at a tertiary-care hospital in France. Patients enrolled from April 2016 to August 2019 had been referred to the clinic for establishing a gout diagnosis or for help managing the condition. All participants underwent DECT and ultrasound of the feet/ankles and knees.

Patients were classified as having gout based on the presence of MSU crystals in the SFA by polarized light microscopy. A second, silver standard, diagnosis used the 2015 ACR–EULAR gout classification criteria score of ≥ 8 but  excluded DECT and ultrasound scores.

Of the 147 patients in the final cohort, 86%were male. The mean age of participants was 64.7 years old with a mean duration of symptoms of 9.2 years. Of the 147 participants, 131 were clinically diagnosed with gout by the attending rheumatologist. Forty-eight patients underwent SFA from joint aspiration. Of these, 38 had MSU crystals and 10 were negative for MSU crystals. One hundred and thirteen patients (113) scored 8 points or higher in the modified 2015 ACR-EULAR gout classification criteria or had MSU crystals in a joint aspiration, and so were considered positive in the silver standard.

As compared with the gold standard, DECT outperformed feet/ankles ultrasound, with a sensitivity of 87% versus 84%; specificity of 100% vs 60%; positive predictive value of 100% versus 89%; and negative predictive value of 67% versus 50%. Compared with the silver standard, DECT performed similarly but with lower accuracy.

Combining both feet/ankles DECT and feet/ankles ultrasound, or knees DECT and knees ultrasound resulted in a numerically higher sensitivity, and for feet ankles, a higher negative predictive value compared with DECT alone. However, overall accuracy was lower when combined.

The researchers noted that the DECT scan of the feet/ankles had the highest overall accuracy and DECT had higher accuracy than ultrasound for both feet/ankles and knees. They also found that there was no improvement in diagnostic accuracy when DECT and ultrasound were combined.

The takeaway for rheumatology clinicians, wrote the study’s authors, is that “DECT alone, particularly of the feet/ankles, may offer the best overall performances for the diagnosis of patients with suspected gout.”2

“It seems that you should get higher predictive values and higher accuracy against the gold standard with DECT of the feet, and DECT of the knee comes pretty close,” says Jasvinder Singh, MD, MPH, professor of medicine at the University of Alabama at Birmingham’s Division of Clinical Immunology and Rheumatology, and lead author of the study. “Ultrasound numbers are a little lower than that.”

Dr. Singh adds that “It’s possible that if you take a different sample from primary care your numbers may be different for either or both [DECT and ultrasound].”

Scoring System

Beyond diagnosis, gout presents challenges in monitoring the progress of the disease in patients with long-term chronic illness. A separate recent study offers some insight on this front. The paper, published this January 2021 in Seminars in Arthritis and Rheumatism,3 presented a consensus-based, semi-quantitative ultrasound scoring system for grading gout lesions. The scoring system was developed by a working group of rheumatologists from 14 countries – the Outcome Measure in Rheumatology (OMERACT) Gout Group.

Though the working group set out to define and validate a set of standard outcome measures to be used to evaluate gout in clinical trials, this system can be useful for clinicians as well. Sara Nysom Christiansen, PhD, of the Department of Clinical Medicine at the University of Copenhagen and lead author on the study, explains that the “scoring system was developed for use in the monitoring of gout patients.” This was the first such scoring system for grading ongoing gout lesions using ultrasound.

The analysis found that ultrasound could be useful in monitoring gout in patients with chronic disease. Christiansen and colleagues wrote, “In routine clinical practice, ultrasound monitoring of gout patients could potentially assist the treating physicians by showing if the desired reduction of crystals is achieved.” However, they also point out that the “relevance of systematic use of ultrasound during therapy has yet to be demonstrated.”3

 

Last updated on: June 1, 2021
Continue Reading:
Gout Diagnosis and Management: Updated Treatment Guidelines
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