Background/Purpose: Gout is associated with chronic kidney disease, but how the kidney function evolves when gout is treated with urate lowering therapy (ULT) is still a matter of debate. Gouty nephropathy is led by crystal deposition in renal medulla, so we hypothesized that patients with a high monosodium urate (MSU) crystal burden could have the highest potential of benefiting from effective crystal depletion in the kidneys. Joint ultrasound provides an assessment of the extent of MSU crystal deposition within joints (the double contour (DC) sign) and within tissues (tophi). The objective of this study was to determine if the burden of MSU crystals as assessed by ultrasound could predict kidney response to ULT in gout patients.

Methods: Gout patients from two referral centers in Spain (Alicante) and France (Lille) requiring ULT initiation were recruited to undergo baseline ultrasound scans and a 1-year follow-up. Ultrasound scans assessed 6 joints for the presence of the DC sign and tophi. Demographic data, comorbidities, treatments, gout history, biological data including the estimated glomerular filtration rate (eGFR) and serum urate levels, were collected at the baseline visit and at the month 12 visit. A 5-point change in the eGFR at month 12 was considered significant. The number of joints affected with the DC sign and presence of tophi were compared between patients improving, preserving and degrading their eGFR using the Khi-2 and Mann-Whitney-Wilcoxon tests respectively.

Results: A total of 165 patients were recruited (n=81 from Alicante and n=84 from Lille) aged 63 years old (±14.5), predominantly male (86.1%) and with 7.5 years (±9.8) of gout duration. Baseline eGFR was 75.2 ml/min/1.73m² (±23.9) and serum urate levels were 8.4 mg/dL (±1.8). Overall, 81.0% of patients had ultrasound tophi and the number of joints with the DC sign was 1.4 (±1.3).

At month 12, 37 patients were lost to follow-up. A target serum urate level below 6.0mg/dL was reached for 88 patients (70.4%) and eGFR was 72.6 ml/min/1.73m² (±23.4). Overall, 16.4% of patients had significantly improved their eGFR, while 31.2% degraded. Patients improving their eGFR numerically achieved more frequently the serum urate target below 6.0mg/dL (83.3%) than those degrading their eGFR (64.9%) (p=0.27). Neither the presence of ultrasound tophus (p=0.53 and 0.75) nor the number of joints with the DC sign (p=0.23 and 0.18) were associated to the improvement or degradation of the renal function. In the subgroup of patients achieving serum urate levels below 6.0mg/dL at month 12, all  (100%) patients improving their eGFR had an ultrasound tophus versus 87% in those not improving (p=0.35), and the number of joints with the DC sign was 1 [1 ; 2] versus 1 [0 ; 2] (p=0.83).

Conclusion: The MSU crystal burden assessed by ultrasound does not help predict the evolution of renal function during the first year of ULT, likely because ultrasound signs of depositions (especially tophi) are quite constant in patients with gout. The study was not sufficiently powered to establish a clear link between reaching the target serum urate level and preserving/improving the renal function.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/renal-evolution-during-the-first-year-of-urate-lowering-therapy-according-to-sonographic-joint-deposition-data-from-the-lille-alicante-inception-cohort/