The absence of accepted standardized methods for monitoring tophaceous gout limits the ability to track tophus progression or regression. This multicenter study assessed intra- and interrater reproducibility of a simple and direct physical measurement.
The quantitative evaluation was the area (mm2) of each measurable tophus and was determined independently by 2 raters on 2 occasions within 10 days. Intra- and interrater reproducibilities were determined by calculating mean differences and average percentage differences (APD) in measurements of areas for the same tophus at each of 2 visits and by each rater, respectively.
Fifty-two tophi were measured in 13 subjects: 22 on the hand/wrist, 16 on the elbow, and 14 on the foot/ankle. The mean (+/- SD) difference in tophus areas between visits was -0.2 +/- 835 mm2 (95% CI -162 to 162 mm2) and the mean (+/- SD) APD was 29% +/- 33%. The mean (+/- SD) APD between raters was 32% +/- 27%. The largest variations in measurements were noted for elbow tophi and variations were least for well demarcated tophi on the hands.
This simple and reproducible method can be easily utilized in clinical trials and in practice as a measure of efficacy of urate-lowering treatment in tophaceous gout. Among factors contributing to variability in these measurements were the anatomic site of tophi and rater experience with the method. Restriction of measurements to well circumscribed hand or foot tophi could improve reliability, but major changes, as expected with effective therapy, can clearly be documented with this simple technique.