Roles of USG and DECT scan in gout diagnosis
What are the roles of ultrasonography and dual energy computed tomography (DECT) scan in gout diagnosis?
• Ultrasonography: musculoskeletal ultrasound can show a superficial, hyperechoic band (deposition of urate crystals) on the surface of articular cartilage (“double contour sign”) in gout. Tophi appear as nonhomogeneous material surrounded by an anechoic rim. Although highly operator-dependent, recent studies have shown the sensitivity of ultrasound for gout diagnosis to be 77%, with a specificity of 84%.
• DECT scan: this is a CT scanning technique in which two x-ray tubes with different voltages are aligned at 90-degree angles to one another. This allows identification of MSU deposits because the chemical composition of urate causes less attenuation of x-ray photons tracking through it compared with bone calcium. Thus, urate deposits can be distinguished from surrounding tissues with a high degree of sensitivity and specificity. However, false-negative findings have been reported early in the course of gout, while false-positives most commonly accompany degenerative arthritis of the knee.
