R. Gancheva ¹, T. Kundurzhiev ², Z. Kolarov ¹, A. Koundurdjiev ³
¹ Clinic of Rheumatology, University Hospital St. Iv. Rilski, ² Faculty of Public Health, ³ Clinic of Nephrology, University Hospital St. Iv. Rilski, Medical University, Sofia
Background: It is not clear whether monosodium urate (MSU) crystal deposits in the joints of gout patients (pts) proven by ultrasound (US) are related to an increased risk of cardiovascular complications. There is insufficient data whether these deposits are connected to impaired renal function, changes in renal blood flow and nephrolithiasis in pts in the spectrum of gout and in individuals who have inflammatory arthritis with accompanying asymptomatic hyperuricemia.
Objectives: To establish the association between US burden with MSU crystals in the joints and renal morphology, blood supply and function in gout pts, individuals with asymptomatic hyperuricemia and no sign of inflammatory arthritis and psoriatic arthritis pts with asymptomatic hyperuricemia.
Methods: The study is cross-sectional. A total of 121 consecutive pts were included, divided into 85 pts with gout - 63 males and 22 females aged 57.7±14.1 years; 27 subjects with asymptomatic hyperuricemia and no sign of inflammatory arthritis - 13 males and 14 females aged 53.4±17.2 years and 9 psoriatic arthritis pts with asymptomatic hyperuricemia - 2 males and 7 females aged 61.2±14.4 years. Glomerular filtration rate (GFR) was estimated by using the Cockroft-Gault formula. Pts underwent US of both kidneys and US of the joints of the hands, elbows, knees, ankles and feet. US measurements of the kidneys were done with 3.5 MHz transducer, working with pulse Doppler frequency of 2.5 MHz. We judged for intrarenal blood flow by determining the renal resistive index (RRI) at the level of interlobar arteries. US of the joints was conducted with a high-frequency, linear transducer, 4-15 MHz. The existence of double contour sign, intra-tendinous MSU aggregates, snow storm, tophi, tophi with erosions, or a combination of these US features was assessed. Data were analyzed by Chi-Square, Mann-Whitney, Kruskal Wallis, ANOVA and multiple logistic regression.
Results: The distribution of chronic kidney disease (CKD) was comparable among pts with gout (45.6%), asymptomatic hyperuricemia (44.0%) and subjects with psoriatic arthritis (44.4%), (p=1.000). In the groups there was no difference in the proportion of pts treated with diuretics (p=0.948). The frequency of CKD (p=0.534) and nephrolithiasis (p=0.438) was equal in pts with and without MSU crystal deposits. In individuals with crystals in the joints RRI was higher (p=0.035) and kidneys were smaller (p=0.014), but renal parenchymal thickness (p=0.893) and echogenicity (p=0.291) were comparable. Subjects with MSU crystals in two or more joints, compared to those with MSU crystal deposits in one joint and pts without crystal deposits, had the highest RRI (p=0.002), but GFR (p=0.115), renal parenchymal thickness (p=0.636), echogenicity (p=0.107) and frequency of nephrolithiasis (p=0.438) were similar. Compared to gout pts the risk of MSU crystal accumulation in the joints of asymptomatic hyperuricemia group was lower by 82.7%, OR=0.173 (95% CI; 0.060 - 0.498, p=0.001), while in psoriatic arthritis pts the risk was lower by 82%, OR=0.180 (95% CI; 0.038-0.861, p=0.032).
Conclusions: We suppose that the accumulation of MSU crystals in the joints is associated with the accumulation of crystals in the renal interstitium. This may explain the smaller kidney size, decreased intrarenal blood flow and the lack of change in renal parenchyma in pts with US MSU crystals in the joints.