Double Contour Sign May Be Useful in Distinguishing Between Gout and CPPD

The double contour sign, as seen on ultrasound, may help to differentiate between gout and calcium pyrophosphate deposition (CPPD), according to study results published in Rheumatic and Musculoskeletal Diseases.

The aim of the cross-sectional analysis was to evaluate the role of the double contour in differentiating between gout and CPPD, as well as whether using ultrasound dynamic assessment can improve the accuracy of the double contour sign in diagnosing gout.

Data from 2 prospective cohort studies and a cross-sectional case control study between September 2019 and June 2022 were included in the analysis.

A total of 81 patients with gout and 84 patients with CPPD underwent ultrasound assessment, of whom 47 (58.0%) patients with gout and 9 (10.7%) with CPPD had a static ultrasound image, indicating a double contour sign in 1 or more joints (57 joints in gout; 13 joints in CPPD).

During the dynamic assessment of patients with gout with ultrasound evidence of the double contour sign, the sign moved with the hyaline cartilage in all 57 joints. However, in patients with CPPD disease with ultrasound evidence of the double contour sign, the sign moved in the opposite direction to the hyaline cartilage in 10 of the 13 joints, indicating the presence of a pseudo sign (P <.01).

In all the 47 patients with gout, the double contour sign moved with the hyaline cartilage. However, in 7 (77.8%) of the 9 patients with CPPD, there was a pseudo double contour sign present, moving in the opposite direction to the hyaline cartilage, which was statistically significant (P <.01). 

The double contour sign underwent a static assessment, which yielded 58.0% (95% CI 46.5%-68.9%) sensitivity, 89.3% (95% CI 80.6%-95.0%) specificity, and 73.9% (95% CI 66.5%-80.5%) for gout in the group with gout and CPPD.

Study limitations included that there was only 1 sonographer conducting all ultrasound examinations at a single center; the small sample size of patients with CPPD; and the lack of generalizability of the pseudo double contour sign to other joints, except the knees, elbows, and metacarpophalangeal joints.

The study authors concluded, “The dynamic assessment of the [double contour] sign may help [ultrasound] to differentiate the DC sign due to [monosodium urate] crystals from the pseudo [double contour] sign seen in CPPD disease, as they move in opposite directions.”

Disclosure: Multiple study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.