Ultrasonographic image in Double contour sign, suggestive of monosodium urate crystal deposition in hyaline cartilage.
Keywords:
Ultrasound, Double contour sign, GoutAbstract
Context: Microcrystalline arthropathies are diseases caused by deposition of crystals within joint and periarticular tissues. Three types of crystals involved in these diseases are monosodium urate, calcium pyrophosphate crystals, and basic calcium phosphate crystals (1). In the case of gout, hyaline cartilage is often the site of monosodium urate crystal deposits, revealing the "Double Contour" (DC) sign, which is a hyperechoic band over the chondrosynovial (superficial) margin, which increases the superficial cartilage interface to a thickness similar to that of subchondral bone (2). (Fig. 1).
Significance: The DC sign, along with other basic lesions such as tophi and aggregates, is a key ultrasound feature in the diagnosis of gout. The sensitivity and specificity of the DC sign vary between 42% and 87.8%, and 64.1% and 97%, respectively. The highest sensitivity is in the metatarsophalangeal joints, followed by the knees and metacarpophalangeal joints (3-4).
Combining the DC sign with power Doppler signals and elevated serum uric acid levels can increase the specificity for gout to 90% (3). Because of this, the double contour sign has been included in the new gout classification criteria proposed by the American College of Rheumatology and EULAR, reinforcing its importance in diagnosing this disease (5).
In conclusion, the double contour sign is a significant ultrasound indicator for diagnosing gout.
Figure 1: Right knee with double-contour sign (DC sign=white arrow; subchondral bone=arrowhead) in a longitudinal and transverse view of the hyaline cartilage (C and D) in a healthy knee, showing only hyaline cartilage and subchondral bone (arrowhead).
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© Instituto Nacional de Rehabilitación Luis Guillermo Ibarra Ibarra under a Creative Commons Attribution 4.0 International (CC BY 4.0) license which allows to reproduce and modify the content if appropiate recognition to the original source is given.
