Tristan Pascart

Objectives To determine the clinical associations and predictive value of two thresholds of negative dual-energy CT (DECT) for MSU crystal deposition in gout patients initiating urate-lowering therapy (ULT) and identify which threshold is more clinically relevant. Methods Patients from the CRYSTALILLE cohort with a diagnosis of gout naïve to ULT with baseline DECT scans of the knees and feet were selected. Two thresholds of positivity for DECT detection of MSU crystal deposition were considered (<0.01 cm3 and <0.1 cm3). Baseline characteristics and the prediction of key outcomes after ULT initiation, including reaching serum urate (SU) levels <6.0 and 5.0 mg/dl and occurrence of flares at 6, 12 and 24 months, associated with both thresholds of negative DECTs were compared with those of patients having positive DECT scans. Results A total of 211 patients, median age 66.2 years [interquartile range (IQR) 57–75.8], with a median symptom duration of 3 years (IQR 0–7.8) were included. A total of 38/211 (18%) and 90/211 (43%) had negative DECT scans for the 0.01 and 0.1 cm3 thresholds, respectively. Factors associated with negative DECT scans were younger age, shorter symptom duration and an absence of cardiovascular disease for both volume thresholds. A total of 9/39 (23.1%), 3/26 (11.5%) and 1/18 (5.6%) patients with <0.1 cm3 MSU crystals had flares at 6, 12 and 24 months, respectively, compared with 18/45 (40.0%), 9/36 (25.0%) and 2/18 (11.1%) patients with ≥0.1 cm3 (P > 0.05). Overall, 95 patients (68.3%) reached SU levels <6.0 mg/dl and 68 (48.9%) reached levels <5.0 mg/dl, without any difference between positive and negative DECTs, with ULT dosages that tended to be lower in patients with negative DECTs. Conclusion The 0.1 cm3 threshold was better correlated with clinical presentation and evolution than the 0.01 cm3 threshold. Gout patients with negative DECTs exhibit milder disease and a lower comorbidity burden. They do not exhibit particularly easy-to-treat hyperuricaemia but they may have a lower risk of flares.