Imagery as Biomarker of Gout (TIGER)

The objective of this study is to determine whether MSU crystal deposits visualized on ultrasound and/or DECT are associated with the development of symptomatic gout (according to ACR 2015 / EULAR criteria) over 5 years in hyperuricemic individuals.

Cross-sectional studies have shown that 17% to 86% of people with apparently asymptomatic hyperuricemia have ultrasound evidence of monosodium urate (MSU) crystal deposition. These observations suggest that this deposition constitutes the first stage of the clinical gout syndrome, which has led to a revised model of disease progression and staging. However, no longitudinal studies have been undertaken to determine whether such findings are needed for the development of gout, or to investigate pathological mechanisms responsible for the transition from asymptomatic crystalline deposit to gout. Only a prospective cohort study of people at risk who are carefully and regularly followed can answer such questions. Dual-energy computed tomography (DECT) and ultrasound are the two imaging techniques that allow the visualization and quantification of MSU crystals. Ultrasound is the most widely used technique; it allows the identification of the deposit of crystals of on the surface of the cartilage (double contour sign) and of the tophi. The DECT can detect the deposition of MSU crystals in soft tissues as long as the amount of crystals exceeds the spatial resolution of the machine (about 250 μm). The international collaborative study TIGER (Transitions in gout research study) aims to address the question of the predictive value of the deposition of MSU crystals "silent" in the development of gout, through an international cohort (7 countries) including 907 asymptomatic hyperuricaemic individuals. These individuals will have initial ultrasounds to investigate the presence of MSU crystal deposits and a 5-year follow-up. Given the aforementioned ultrasound reproducibility issues, DECT analyzes will be added to the baseline assessment of TIGER participants to provide exploratory data on DECT as a potential biomarker for the impending development of gout.

Patients at high risk for gout due to elevated serum urate concentrations (≥ 8 mg/dL) will be included. The participants included will be followed for a period of 60 months, with an initial visit, a final visit as well as an additional visit in case of suspicion of gout. The presence of symptoms suggestive of gout will be evaluated during regular contact with the participants: a telephone call every 6 months as well as a postal or electronic mail every 3 months. Participants will be asked to contact the investigator if new symptoms or relevant medical events occur. Blood (32.5 ml maximum) and urine (4 ml) samples will be taken from participants who have given their specific consent for a biological collection with a particular genetic aim.

DECT and ultrasound will be performed to clarify the pathological mechanisms responsible for the transition from asymptomatic crystalline deposition to gout, and the mechanisms involved in the transition from hyperuricemia to de novo crystalline deposition.

Development of symptomatic gout will be determined according to ACR/EULAR 2015 criteria at any time during the follow-up period. This scale is based on clinical, laboratory and imaging parameters. More than 8 points is considered as Gout. 0 is considered as absence of gout

Inclusion Criteria: Serum urate level ≥ 80 mg/L on inclusion, No current or previous clinical symptoms of gout (including clinically apparent flares or tophus), Between 18 and 80 years old, Able to give informed consent. Exclusion Criteria: GFR (glomerular filtration rate) <30 ml / min / 1.73 m² or dialysis, Serious illness with a poor prognosis of less than 5 years, Autoimmune inflammatory arthritis, Change of geographical area within 5 years, Previous analysis of synovial fluid showing crystals of MSU, Presence of subcutaneous tophi, Taking a hypouricaemic treatment (allopurinol, probenecid, benzbromarone, febuxostat, lesinurad), canakinumab, anakinra or colchicine, Uricemia observed only after an acute decompensation of comorbidity Pregnant or breastfeeding women