| Purpose:To evaluate the intraobserver and interobserver reproducibility of the tophus urate volume, erosion volume measurements in patients with gout by using DECT (Dual-energy computed tomography) scans. And to separately analyze the relationship between urate burden within tophus and bone erosion according to tophus locations, further to explore the role of urate within tophus in the formation of bone erosion.Methods:Fifty-one subjects with chronic gout underwent DECT scans of hands/wrists or feet/ankles. Two independent observers measured the tophus urate volumes and bone erosion volumes using the automated volume assessment software and each observer assessed images twice with the interval of one week. Intraobserver and interobserver reproducibility were analyzed by intraclass correlation coefficient (ICC) and limits of agreements analysis. The relationships between urate burden within tophus and bone erosions were separately analyzed according to the tophus locations (intraosseous, intraarticular and soft tissue tophi). Results:Of the51study subjects,40(78%) were in feet/ankles,11(22%) were in hands/wrists. Of the total534index tophi identified on DECT,59(11%) were located in hands/wrists,475(89%) in feet/ankles. The mean individual tophus urate volume was139.14mm3(median6.58; range0.12to40797.37). The intra-and interobserver ICC for tophus urate volumes were1.000(95%CI1.000,1.000) and1.000(1.000,1.000). Bone erosions identified by both observers were present in301bones. Of these erosions,42(14%) were located in hands/wrists,259(86%) in feet/ankles. The mean individual erosion volume was218.00mm3(97.62;3.43to5319.02). The intra-and interobserver ICC for erosion volumes were0.998(0.998,0.998),0.999(0.998,0.999). There were118tophi with correlated erosions,13(11%) were located in hands/wrists,105(89%) located in feet/ankles. According to the location and region of these tophi, they were classified into intraarticular tophi (n=45), intraosseous tophi (n=19), soft tissue tophi (n=1), intraarticular-intraosseous tophi (n=22), intraarticular-soft tissue tophi (n=9), intraarticular-intraosseous-soft tissue tophi (n=22). Positive correlations were demonstrated between tophus urate volumes and erosion volumes in intraosseous tophi, intraarticular-intraosseous tophi, intraarticular-intraosseous-soft tissue tophi (r=0.645-0.880, p<0.001), but no significant correlation was demonstrated in intraarticular tophi, intraarticular and soft tissue tophi (r=0.026-0.040, p=0.796-0.947). There were moderate positive correlations between total tophi urate volumes and total erosion volumes (rs=0.574, p<0.001) in feet/ankles and no significant correlation in hands/wrists (rs=0.045, p=0.894).Conclusion:This study demonstrated a high reproducibility of tophus urate volumes, erosion volumes measurements using DECT, which make those methods as potientially valuable measures in tophus and bone erosion evaluation. The tophus location was correlated with bone erosion formation and the intraosseous tophus has the greatest impact. Tophaceous deposits eroded into the bone was the crucial cause of bone erosion formation in gout. |
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