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Bone erosions, which are associated with long-term damage and disability, are common in patients with gout and have been linked with specific clinical and ultrasound-detected factors, Chinese researchers reported.

Among 980 patients with gout, 44% had bone erosions seen on ultrasound, according to Hai B. Chen, MD, and colleagues from Shanghai Jiaotong University Affiliated Sixth People's Hospital in Shanghai.

Factors that were identified as being independently associated with bone erosions were age, duration of gout, the presence of tophi, and ultrasound-detected synovial hypertrophy, they researchers reported online in .

The presence of erosions and tophi is included in for considering urate-lowering treatment in gout, with the goal of preventing flares, kidney damage, and joint damage. "Thus, early and accurate detection of erosions is important for diagnosis, treatment, and monitoring of gout," they wrote.

Ultrasound has increasingly been recognized as a useful and low-cost imaging technique for the accurate diagnosis of gout and for detecting complications such as erosions and tophi. However, few studies have examined the prevalence of these disease manifestations and their risk factors, so the Shanghai researchers conducted a retrospective study of patients seen at their center from 2015 to 2017.

Among the 980 patients included in their analysis, 92.9% were men, and mean age was 50.3. A total of 431 had ultrasound evidence of erosions, with 78.4% of those being located at the first metatarsophalangeal joint, 24.6% at the ankles, and 8.8% at the knees. A single erosion site was seen in 51.5%, 32% had two erosions, and the remainder had three or more.

Patients with erosions were older (54.6 vs 47, P<0.001) and had longer disease duration (9.2 vs 5.2 years, P<0.001), and had more frequent gout flares in the past year (9 vs 4.2, P<0.001) than those without erosions. They also had higher rates of hypertension, kidney dysfunction, and hyperglycemia.

Differences between patients with and without erosions also were observed in the ultrasound findings. For instance, 62.4% of patients in the erosion group had detectable tophi compared with 25.1% of the non-erosion group (P<0.001). In addition, 73.5% of the erosion group had the double contour sign compared with 57.6% of the non-erosion group (P<0.001), and articular synovial hypertrophy was seen in 59.4% compared with 48.3% (P=0.001). Joint effusions were more common in the non-erosion group (78.7% vs 53.1%, P<0.001).

On a multiple regression analysis, these factors were positively associated with bone erosions:

• Tophi: OR 4.218 (95% CI 3.092-5.753, P<0.001)
• Synovial hypertrophy: OR 1.870 (95% CI 1.378-2.538, P<0.001)
• Duration of gout: OR 1.053 (95% CI 1.027-1.079, P<0.001)
• Age: OR 1.017 (95% CI 1.007-1.027, P=0.001)

A negative correlation was seen for joint effusions (OR 0.316, 95% CI 0.231-0.432, P<0.001).

Further analysis determined that increased numbers of tophi exacerbated risks of erosions. Compared with patients without tophi, those with one or two tophi had an odds ratio of 3.624 (95% CI 1.092-12.032, P=0.035), which rose to 10.571 (95% CI 2.884-38.744, P<0.001) for those with three or four tophi, and to 15.390 (95% CI 3.866-61.268, P<0.001) for those with five or more.

In contrast, the size of the tophi did not influence risk, with nonsignificant differences between those whose tophi were <10 mm, 10 to 20 mm, or >20 mm.

Various mechanisms could contribute to the development of bone erosions in gout, according to the researchers. Monosodium urate crystals promote the development of osteoclasts between bone and tophi and also increase osteoclastogenesis in fibroblasts, chondrocytes, and macrophages. A cytokine milieu that promotes erosions also can be encouraged by upregulation of macrophage colony stimulating factor and receptor activator of nuclear factor kappa-B ligand.

The finding that joint effusions had a negative correlation with bone erosions also was noteworthy. The authors wrote, "We speculate that, because bone erosion occurs through an 'outside-in' mechanism, exudative inflammation may prevent direct invasion of the tophus (or granulomatous synovitis) through the articular cartilage into bone."

"These results suggest that long-term inflammatory rather than acute inflammatory stimuli that promote progressive synovial thickening are a risk factor for bone erosion," they noted.

The study suggested that early diagnosis and close urate control to prevent the deposition of urate crystals may be the optimal way of minimizing the risk of bone erosions in gout.

Study limitations included its relatively small number of patients and the inability of ultrasound to assess the depth of erosions.

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