UltraSound Evaluation in Follow-up of Urate-Lowering therapy in gout phase 2 (USEFUL-2): duration of flare prophylaxis.

OBJECTIVES To determine whether changes in ultrasonography (US) features of monosodium urate crystal deposition is associated with the number of gouty flares after stopping gout flare prophylaxis. METHODS We performed a 1-year multicentre prospective study including patients with proven gout and US features of gout. The first phase of the study was a 6-month US follow-up after starting urate-lowering therapy (ULT) with gout flare prophylaxis. After 6 months of ULT, gout flare prophylaxis was stopped, followed by a clinical follow-up (M6 to 12) and ULT was maintained. Outcomes were the proportion of relapsing patients between M6 and M12 according to changes of US features of gout and determining a threshold decrease in tophus size according to the probability of relapse. RESULTS We included 79 gouty patients (mean [± SD] age 61.8 ± 14 years, 91% males, median disease duration 4 [IQR 1.5; 10] years). Among the 49 completers at M12, 23 (47%) experienced relapse. Decrease in tophus size ≥ 50% at M6 was more frequent without than with relapse (54% vs 26%, P= 0.049). On ROC curve analysis, a threshold decrease of 50.8% in tophus size had the best sensitivity/specificity ratio to predict relapse (AUC 0.649 [95% confidence interval 0.488 ; 0.809]). Probability of relapse was increased for patients with a decrease in tophus size <50% between M0 and M6 (OR 3.35 [95% confidence interval 0.98; 11.44]). CONCLUSION A high reduction in US tophus size is associated with lower probability of relapse after stopping gout prophylaxis. US follow-up may be useful for managing ULT and gout flare prophylaxis.