Gout

Ultrasound backed for diagnosis of gout


Ultrasound that shows deposition of monosodium urate crystals has high specificity and positive predictive value for a diagnosis of gout when conducted in routine clinical settings, data from the SUGAR study has shown.

SUGAR, primarily designed to update gout classification criteria, enrolled patients with at least one swollen joint or a subcutaneous nodule “who conceivably may have gout”.

The double contour sign, tophus and a ‘snowstorm’ appearance each correlated with the presence of MSU crystals identified on arthrocentesis.

Data were accumulated from 824 patients at 25 centres around the world. Ultrasonographers had not received specific training for the study, had varying levels of experience and used differing equipment. In contrast, previous smaller studies exploring the utility of ultrasound were generally restricted to single specialist centres with high levels of expertise and performed in patients with advanced disease.

“A positive ultrasound finding…was associated with suspected tophi on examination, higher serum urate and abnormal radiographic findings,” the researchers wrote in Arthritis and Rheumatology.

“While ultrasound performs best in patients who would likely be more easily diagnosed without imaging, ultrasound is still useful in patients without obvious gout from examination (eg, without tophi, without MTP tenderness or swelling) and specificity remains high in these subgroups.”

The research team said the study was a unique contribution as it reflected real-life multicentre experience. While the double contour sign and tophus had been investigated in some detail in the past, the SUGAR data also demonstrated the value of the ‘snowstorm’ finding.

An editorial noted that gout remains under-recognised and under-treated, even though it is highly responsive to therapy.

Reluctance to perform joint aspiration to identify MSU crystals is among the complex reasons for inadequate management, and ultrasound offered an alternative approach.

“Although not a difficult procedure, joint aspiration requires training, practice and operator comfort, and most primary care and many emergency room doctors eschew joint aspiration in favour of clinical judgment,” it said.

“However, clinical judgment is not always correct, and the ability to employ alternative approaches to achieve an accurate gout diagnosis will be critical to improving the health of our patients.”

It cautioned that ultrasound signs typical of gout did not exclude other possible causes of joint pain and inflammation, including septic arthritis. “The diagnosis of gout will continue to require a clinical context,” it said.

 

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