Abstract
IntroductionDual-energy computed tomography (DECT) has potential for monitoring urate deposition in patients with gout. The aim of this prospective longitudinal study was to analyse measurement error of DECT urate volume measurement in clinically stable patients with tophaceous gout.MethodsSeventy-three patients with tophaceous gout on stable therapy attended study visits at baseline and twelve months. All patients had a comprehensive clinical assessment including serum urate testing and DECT scanning of both feet. Two readers analysed the DECT scans for the total urate volume in both feet. Analysis included inter-reader intraclass correlation coefficients (ICCs) and limits of agreement, and calculation of the smallest detectable change.ResultsMean (standard deviation) serum urate concentration over the study period was 0.38 (0.09) mmol/L. Urate-lowering therapy was prescribed in 70 (96%) patients. The median (interquartile range) baseline DECT urate volume was 0.49 (0.16, 2.18) cm3, and change in DECT urate volume was -0.01 (-0.40, 0.28) cm3. Inter-reader ICCs were 1.00 for baseline DECT volumes and 0.93 for change values. Inter-reader bias (standard deviation) for baseline volumes was -0.18 (0.63) cm3 and for change was -0.10 (0.93) cm3. The smallest detectable change was 0.91 cm3. There were 47 (64%) patients with baseline DECT urate volumes <0.91 cm3. Higher serum urate concentrations were observed in patients with increased DECT urate volumes above the smallest detectable change (P = 0.006). However, a relationship between changes in DECT urate volumes and serum urate concentrations was not observed in the entire group.ConclusionsIn patients with tophaceous gout on stable conventional urate-lowering therapy the measurement error for DECT urate volume assessment is substantially greater than the median baseline DECT volume. Analysis of patients commencing or intensifying urate-lowering therapy should clarify the optimal use of DECT as a potential outcome measure in studies of chronic gout.
Highlights
Dual-energy computed tomography (DECT) has potential for monitoring urate deposition in patients with gout
High sensitivity (78% to 100%), high specificity (79% to 100%) and intraobserver and interobserver reproducibility of DECT urate volume measurements have been reported [1,2,3,5,6], suggesting that this tool may be useful for both diagnosis and monitoring of patients with gout
For serum urate tests conducted at baseline and year 1, the mean (SD) value was 0.38 mmol/L (0.09)
Summary
Dual-energy computed tomography (DECT) has potential for monitoring urate deposition in patients with gout. The aim of this prospective longitudinal study was to analyse measurement error of DECT urate volume measurement in clinically stable patients with tophaceous gout. A systematic analysis of the sensitivity to change and measurement error of DECT has not been published This information is essential in determining the role of DECT as a valid outcome measurement modality for use in clinical studies of chronic gout [9,10]. The primary aim of this prospective, longitudinal study was to analyse measurement error of DECT in the assessment of urate deposition in clinically stable patients with tophaceous gout. We wished to examine the relationships between DECT volumes and clinical features of gout, as well as the correlations between changes in these measures
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