Imagery as Biomarker of Gout

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.

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