Methods of assessment of tophus and bone erosions in gout using dual-energy CT: reproducibility analysis.

This study aims to evaluate the intraobserver and interobserver reproducibility of the tophus urate volume, erosion volume, and the erosion score measurements in patients with gout by using dual-energy CT (DECT) scans comparing their bone erosion volumes against bone erosion scores and also to determine a valid measure of joint destruction in chronic gout. Sixty-six subjects underwent DECT scans of the hands or feet. Two independent observers measured the tophus urate volumes and bone erosion volumes using automated volume assessment software and the erosion scores based on the rheumatoid arthritis magnetic resonance imaging score (RAMRIS). The intraobserver and interobserver reproducibility were analyzed by intraclass correlation coefficient (ICC) and limits of agreements analysis. The relationship between erosion volumes and erosion scores was analyzed. The intraobserver and interobserver ICC for tophus urate volume measurements (n = 636) were 1.000 (95 % confidence interval (95 % CI) 1.000 to 1.000) and 1.000 (95 % CI 1.000 to 1.000), 0.999 (0.999, 0.999) and 0.999 (0.999, 0.999) for bone erosion volumes (n = 350), 0.937 (0.928, 0.946) and 0.899 (0.883, 0.912) for erosion scores (n = 350). Strong positive correlations were demonstrated between individual erosion volumes and scores (r s = 0.914, p < 0.001) as well as total erosion volume and score per patient (r = 0.838-0.867, p < 0.001). This study demonstrated a high reproducibility of tophus urate volumes, erosion volumes, and erosion score measurements using DECT. Erosion volumes show to be a more direct and accurate method to evaluate bone erosion compared with erosion score, strongly supporting it as a superior and standard measure of structural joint damage in gout.