Lariboisiere Hospital, Department of Rheumatology Paris, France
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Background/Purpose: We previously described the frequent occurrence of an hyperechogenic pattern of the renal medulla following crystal deposition in untreated Vietnamese patients with severe tophaceous gout(1), without quantifying the medulla brightness. The aim of the present study was to quantify medulla brightness and investigate correlations with gout characteristics and renal function. Methods: This prospective monocentric study analyzed baseline data of the first 250 patients enrolled in our ongoing prospective cohort at Vien Gut (a decicated medical center for diagnosis and treatment of gout in Vietnam), that aims at describing the effect of urate-lowering drugs (ULDs) on medulla echogenicity and renal function. Inclusion criteria were: i) gout according to the ACR/EULAR criteria, ii) residency in Ho Chi Minh City, Vietnam, iii) no use of ULDs at the time of enrollment and iv) signed informed consent. All patients underwent renal ultrasonography and renal medulla echogenicity assessment by two methods: 1) a semiquantitative scale (grade 0: no medullary hyperechogenic spot; 1: few spots in 1 or 2 pyramids; 2: hyper echoic pattern involving 40-60% of most pyramids; 3: hyper echoic pattern of > 60% of pyramids), and 2) image analysis using image J software to quantify the cortex/medulla echogenicity ratio of the 2 best viewed pyramids. Clinical data were prospectively collected. Univariate proportional odds logistic regression models or linear regression models were used to compare the two methods of medulla rating and to look for correlations with patients ‘features. Multivariable analysis included all statistically significant features, with model selection on the Akaike criterion (AIC). Results: Median age and gout duration of patients (249 men) were 51 and 4 years respectively, 211 had clinical tophi, median eGFR and serum urate were 96.7 mmol/l and 529 mmol/l respectively. Medulla echogenicity was similar in both kidneys in all patients but 2, who differed by one grade; maximal grades were 0 in no patient, 1 in 146, 2 in 84, and 3 in 20 (table 1). Grades correlated negatively with corticex/medulla echogenicity ratios (p=0.0002) and positively with median maximum medulla echogenicity (p< 0.0001) (figure 1). By univariate analysis, medulla echogenicity grades correlated positively with medians of duration of gout, number of tophi, serum urate levels, and creatininemia, hypertension, MTP1 ultrasound features (double contours (graded 0 to 3) and tophus surfaces), and negatively with blood cortisol levels and eGFR; by multivariate analysis, correlations remained significant with numbers of clinical tophi, eGFR, cortisol levels, and MTP1 tophus surfaces (table 1). Median cortical/medullary echogenicity ratio correlated negatively with creatininemia. Conclusion: The two ways of quantifying medulla echogenicity that we used provided consistent results and showed clinically meaningful correlations with patients ‘features , especially renal function. Intersestingly, lower levels of cortisol were also associated, in line with the suspected effect of chronic exogenous steroid intake on tophi.
