Is gouty nephropathy real? It’s a question that has been posed often in rheumatology over the last several decades.
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A new study found 36% of patients with untreated gout at a medical center in Vietnam have diffuse hyperechoic renal medulla as seen on ultrasound, which could indicate the presence of microcrystalline nephropathy. However, the results, published in Kidney International, may raise more questions than answers about the existence of gouty nephropathy and its relation to chronic kidney disease (CKD).
In their study, Thomas Bardin, MD, of the department of rheumatology at Lariboisière Hospital in Paris and colleagues evaluated 502 consecutive patients from Vien Gut Medical Center in Ho Chi Minh City, Vietnam, using B-mode renal ultrasound. The patients were mostly men with a median age of 46 years, body mass index of 25 kg/m2, estimated disease duration of 4 years, and uricemia of 423.2 micromol/L (7.11 mg/dL). Patients had a median estimated glomerular filtration rate (eGFR) of 78 mL/min per 1.73 m2. There was a history of hypertension in 112 patients (22.3%), type 2 diabetes in 58 patients (11.5%), renal lithiasis in 28 patients (5.6%), and coronary heart disease in 5 patients (1%).
While 39% of patients had previously used allopurinol for “a generally short period,” patients were not on urate-lowering therapy at the time of the study. Clinical tophi were present in 279 patients (55.6%), urate arthropathies in 154 patients (30.7%), and 43 patients (10.4%) used steroids daily.
B-mode renal ultrasound showed 181 patients (36%; 95% confidence interval, 32%-40%) had “hyperechoic pattern of Malpighi pyramids compared with the adjacent cortex,” which was “associated with twinkling artifacts” visible on color Doppler ultrasound. There was a significant association between renal medulla hyperechogenicity and patient age, disease duration, use of steroids, clinical tophi, and urate arthropathy (P less than .0001 for all). A significant association was also seen between renal medulla hyperechogenicity and decreased eGFR (P < .0001), proteinuria (P = .0006), leukocyturia (P = .0008), hypertension (P = .0008), hyperuricemia (P = .002), and coronary heart disease (P = .006).
In a multivariate analysis, there was a significant association between renal medulla hyperechogenicity and clinical tophi (odds ratio, 7.27; 95% CI, 3.68–15.19; P < .0001), urate arthropathy (OR, 3.46; 95% CI, 1.99–6.09; P < .0001), estimated gout duration (OR, 2.13; 95% CI, 1.55–2.96; P < .0001), double contour thickness (OR, 1.45; 95% CI, 1.06–1.97; P < .02), and eGFR (OR, 0.30; 95% CI, 0.09–0.89; P < .034).
“The finding was observed mainly in tophaceous gout, which involved a large proportion of our patients who had received very little treatment with urate-lowering drugs and was associated with moderately impaired renal function and urinary features compatible with tubulointerstitial nephritis,” Dr. Bardin and colleagues wrote in the study. The researchers also found “similar features” in 4 of 10 French patients at the Paris Necker Hospital in Paris, and noted that similar findings have been reported in Japan and Korea, which they said may mean hyperechoic medulla “is not unique to Vietnamese patients.”