Discrimination aspects for each method of measurement
| Modality | Reliability | Change sensitivity | Between-group discrimination |
|---|---|---|---|
| Total number of tophi | Data not available | In patients taking effective urate-lowering therapy (ULT), the mean percentage reduction in total number of tophi was 58.5% after up to 3 years of treatment. Effect size 0.47.5 | Demonstrated. A significant difference in the number of tophi was observed with subjects taking 120 mg febuxostat compared with placebo for 28 weeks, p<0.05.6 |
| Tape measure | Intraobserver: intraclass correlation coefficient (ICC) 0.92 (95% CI 0.88 to 0.94), mean difference (SD) −0.2 (835) mm2. Interobserver: site 1, ICC 0.92 (0.86 to 0.96), mean difference (SD) −150 (982) mm2; site 2, ICC 0.85 (0.75 to 0.91), mean difference (SD) 7 (925) mm2.15 | In patients taking effective ULT for up to 3 years, tophus size was reduced 59% using this method of measurement. Effect size 0.48.5 | Not demonstrated4 5 |
| Vernier calliper | Intraobserver: ICC 1.0 (95% CI 0.99 to 1.0), mean difference (SD) −0.72 (2.42) mm. Interobserver: ICC 0.99 (95% CI 0.97 to 0.99), mean difference (SD) 0.45 (−2.30) mm.16 | In a 5-year longitudinal study of ULT, the mean velocity of reduction of the target tophus ranged from 0.57 to 1.53 per month. There was a strong relationship between SU and velocity of tophus regression (r=−0.62, p<0.05). Effect size 1.83.8 | Demonstrated. Compared with allopurinol alone, benzbromarone alone or combination treatment of benzbromarone and allopurinol led to greater velocity of tophus reduction in a 5-year longitudinal study of tophus regression, p<0.01.8 |
| Digital photography | Data not available | After treatment with pegloticase for 3 months, 22% of subjects experienced complete resolution of the target tophus. After 6 months 45% experienced complete resolution.7 Effect size not available. | Demonstrated. Pegloticase treatment (8 mg every 2 weeks) was associated with higher rates of complete resolution than placebo, p=0.006.7 |
| Ultrasonography | Intraobserver: ICC 0.96 (95% CI 0.93 to 0.98) for maximal diameter and 0.98 (95% CI 0.96 to 0.99) for volume. Mean difference (SD) −0.54 (2.81) mm for maximal diameter and −0.15 (0.65) cm3 for volume. Interobserver: ICC 0.83 (95% CI 0.41 to 0.95) for maximal diameter. Mean difference (SD) 1.06 (4.71) mm for maximal diameter.9 | In a longitudinal observational study of ULT, there was a relationship between SU and the reduction in maximal diameter and the volume of tophi (r2=0.47 and r2=0.41, respectively, both p<0.001). Effect size 1.7 for maximal diameter change and 1.93 for volume change.9 | Not demonstrated9 |
| MRI | Intraobserver: ICC 1.0 (95% CI 0.99 to 1.0), mean (SD) difference −0.05 (0.97) cm3. Interobserver: ICC 0.98 (95% CI 0.96 to 0.99), mean (SD) difference 0.89 (2.05) cm3; p=0.02 between observers.20 | Data not available | Data not available |
| CT | Intraobserver: ICC 1.0 (95% CI 1.0 to 1.0), mean difference (SD) −13.1 (50.7) mm3. Interobserver: ICC 0.99 (95% CI 0.98 to 0.99), mean difference (SD) 65.2 (−182.7) mm3.16 | Data not available | Data not available |
| Dual energy CT (DECT) | Data not available | In a 19-month clinical study of 12 patients with tophaceous gout, all responders to ULT (n=10) had a reduction in tophus volume with a median reduction of 64% (p=0.002). Effect size 0.37.28 | Data not available |