A cross-sectional study of 502 patients found a diffuse hyperechoic kidney medulla pattern in patients with severe gout.

We have previously shown that ultrasonography can detect hyperechogenic crystal deposits in the kidney medulla of patients with gout. In this cross-sectional study we investigated the frequency and clinical correlates of hyperechogenic kidney medulla in 502 consecutive primary consultants for gout (ACR/EULAR criteria) at the Vien Gut medical center in Ho Chi Minh City, Vietnam. None of these patients received urate-lowering drugs. Kidney medulla echogenicity on B-mode ultrasonography was compared to that of the kidney cortex. Overall, 36% patients showed a hyperechoic pattern of Malpighi pyramids. On univariate analysis, the pattern was significantly associated with age, estimated gout duration, steroid-dependency, clinical tophi, urate arthropathy, double contour thickness at the scanned joints, coronary heart disease, arterial hypertension, hyperuricemia, proteinuria, leukocyturia, and decreased estimated glomerular filtration rate. On multivariable analysis, the hyperechoic pattern was associated with estimated disease duration, clinical tophi, urate arthropathy, double contour thickness and decreased estimated glomerular filtration rate. No hyperechoic pattern was observed in 515 consecutive consultants without gout. Thus, hyperechoic kidney medulla was frequently demonstrated in Vietnamese patients with tophaceous gout and associated with features of tubulointerstitial nephritis. This finding revives the hypothesis of microcrystalline nephropathy of gout, predominantly seen in untreated gouty patients, which could be an important target for urate-lowering therapy.

Calcium Pyrophosphate Dihydrate Crystal Deposition in Gouty Tophi.

OBJECTIVE: The coexistence of calcium pyrophosphate dihydrate (CPPD) and monosodium urate monohydrate crystals in gouty tophi has rarely been reported. We undertook this study to investigate CPPD crystal deposits in a series of surgically removed gouty tophi and to identify factors associated with these deposits. METHODS: Twenty-five tophi from 22 gout patients were analyzed using polarized light microscopy, field emission scanning electron microscopy (FESEM), and µ Fourier transform infrared (µFTIR) spectroscopy. RESULTS: Tophi consisted of multiple lobules separated by fibrous septa and surrounded by a foreign-body giant cell reaction. CPPD crystal aggregates were identified in 9 of 25 tophi from 6 patients. CPPD crystals were dispersed or highly compacted, localized at the edge or inside the tophus lobules, with some lobules completely filled with crystals. Both monoclinic and triclinic CPPD crystal phases were identified using FESEM and µFTIR. Compared to patients without CPPD, those with CPPD-containing tophi were older (mean 60.5 years versus 47.2 years; P = 0.009), and had longer-term gout duration (mean 17.0 years versus mean 9.0 years; P < 0.05) and tophi duration (mean 10.0 years versus mean 4.6 years; P < 0.01). None of the patients had radiographic chondrocalcinosis of the knee or wrist. CONCLUSION: CPPD crystal formation seems to be a late and frequent event of tophus maturation, occurring more frequently with aging, and could contribute to the speed of tophus dissolution and the apparent persistence of tophus sometimes observed even after effective, long-lasting urate-lowering therapy.