Introduction
Gout is one of the most common inflammatory joint diseases, and is caused by an aberrant purine metabolism and a deposition of monosodium urate crystals (MSU) in and around the joints.1 Its prevalence ranges from <1% to 6.8% amongst different races, and has shown an apparent rising and younger trend in recent years.1 Tophi caused by a long-term deposition of MSU crystals is the characteristic symptom of advanced gout.2 As reported, tophi develops in approximately 12-35% of gout patients.3 However, the clinical significance of tophi is often underestimated. In fact, tophi may lead to several significant complications, such as irreversible joint deformities and dysfunctions, severely limited range of motions, bone destructions and even fractures.4,5 Superficial tophi can cause infections and ulceration.6 It can also cause entrapment neuropathy, such as carpal tunnel syndrome and radiculopathy.7,8 The ideal treatment choice for patients with serious tophi complications is surgery, which has certain risks and may be quite expensive.9 Overall, tophi seriously impacts the life quality and longevity of patients, not to mention a huge economic burden.10
Previous researches have indicated that multiple factors are related to tophi formation, including serum uric acid level, disease duration, age, gender, family history, gout flare frequency, incidence of obesity, hypertension, hyperlipidaemia, renal dysfunction, kidney stone, coronary heart disease, and upper limb joint involvement.2,11,12 Considering the hazards of tophi, it is significant to establish an accurate prediction tool to confirm and evaluate the various influences of the above potential associated risk factors on tophi formation. This is likewise beneficial to the early prevention, diagnosis and treatment of tophi. However, there are no relatively existing studies on this matter. Thus, this study was conducted to develop a simple yet valid prediction model to identify the predictors of tophi formation amongst people with gout.