Demographics and clinical characteristics of the study population
Demographics and clinical characteristics were summarized in Table 1. Among the 202 gout patients, 191(94.55%) were male. The average age was 46.90 years old. Among the 43 hyperuricemia patients, 31(72.09%) were male. The average age was 44.47 years old. BMI in both gout (25.59±3.48) and hyperuricemia (25.64±3.03) patients were higher than normal value (18.5~23.9), and there was no significant difference between the two groups. Serum uric acid (SUA) in gout patients (524.24±79.68) was higher than that in hyperuricemia patients (493.40±66.85), which might be due to the longer course of hyperuricemia in gout group.
The urate crystal deposits in the kidney directly result in chronic urate nephropathy. In table 1, creatinine clearance rate (Ccr) in gout patients (95.55±2.55ml/minute) is lower than that in hyperuricemia patients (106.42±5.54ml/minute). Ccr<80ml/minute were detected in 39.60% (80/202) of gout patients and in 20.93% (9/43) of hyperuricemia patients. Hyperlipidemia and hyperglycemia were known to co-exist with hyperuricemia and gout. In our study, both fasting blood glucose (GLT) and triglyceride (TG) were found higher in gout patients than those in hyperuricemia patients (Table 1). Our results showed more common comorbidities, such as kidney damage and metabolic disorder in gout patients.
Clinical characteristics of gouty attacks in the gout population
We further analyzed the clinical characteristics of the joints with ultrasound abnormalities in the gout population (Table 2). Totally 531 joints including 187 (35.22%) of MTP1, 155 (29.19%) of ankles, 100 (18.83%) of knees, 45 (8.47%) of acrotarsium, 21 (3.95%) of hand joints, 12 (2.26%) of wrist and 11 (2.07%) of elbow in the 202 patients had clinical attacks. There were more right joints showed attacks than left ones although there was no statistical significance. Of the 202 gout patients, the headmost involved joints were 99 (49.01%) on MTP1, 61 (31.20%) on ankle, 21(10.40%) on acrotarsium, 14(6.93%) on knee, 3(1.49%) on wrist and 4(1.98%) on hand joints. The results indicate that attacks more likely occurred on MTP1, ankle and acrotarsium.
Global US findings in the patients with gout and hyperuricemia
In the 202 gout patients, 76.24% (154/202) of patients were detected MSU crystals in at least one of the joints, and 23.76% (48/202) of patients did not present any MSU crystals in the examined joints. MSU crystals were detected in 358 (33.09%) joints of total 1082 examined joints among the gout patients (Table 3.1). There were 277 (77.37%) of the 358 joints with MSU crystals had attacks. In the hyperuricemia patients, MSU crystals were detected in 11 joints among 256 joints underwent US examination and the positive rate was 4.3% (11/256). Interestingly, these 11 joints belonged to 11 patients and each patient had only one joint with positive US signs of MSU crystal deposition (Table 3.1).
In the 1082 joints of the gout patients, 487 joints had at least one attack, while no attacks were reported in 541 joints (Table 3.2). In the 487 joints, 56.88% (277/487) of joints were found MSU crystals using US. Among these joints, 32.65% (159/487), 7.80% (38/487) and 24.64% (120/487) were DCS, HAG and Tophi, respectively.
Synovial lesion and bone erosion in the patients with gout
Beside the US signs of MSU crystal deposition, synovial lesion (i.e., synovial hypertrophy and synovitis) and bone erosion were regularly detected in the patients. In the gout patients, synovial lesion was found in 192 (17.74%) joints and bone erosion was found in 82 (7.58%) joints among total 1082 joints. In the 192 joints with synovial lesion, 24.48% (47/192), 11.98% (23/192), 12.50% (24/192) joints were simultaneously detected DCS, HAG and tophi, respectively. In the 82 joints with bone erosion, 56.10% (46/82), 7.69% (4/82), 75.61% (62/82) of joints were simultaneously detected DCS, HAG and Tophi, respectively (Table 4.1). We further analyzed the correlation between synovial lesion and bone erosion with three different US assessments. The results showed that synovial lesion was related to HAG (p<0.01) (Table 4.2), bone erosion was related to tophi (p<0.001) and DCS (p<0.01) (Table 4.3).
Course time and the MSU crystals in gout patients
Hyperuricemia is the pathogenesis of gout. When the urate level in serum exceeds its saturation concentration, the precipitated urate crystals deposit in joints and soft tissues. In this study, we found that MSU crystal deposition was correlated with serum uric acid (SUA) level (p<0.01) and the duration (p<0.01). Furthermore, a large proportion of patients had no awareness of their SUA level prior to seeking clinical specialists. In the 202 gout patients, only 17.33% (35/202) of the patients came for treatment at their early stage (course<1 year). Majority of them had more than one year gout history (Table 5.1).
In the gout patients, the proportion of US positive signs of MSU crystal deposition were gradually increased, especially DCS and tophi during the process of gout. In the patients with more than 15 years of gout history, DCS and Tophi were detected in 48.18% and 40.00% of joints respectively, while in the patients with less than 1 year of gout history, DCS and Tophi were only found in 6.29% and 5.03% of joints respectively. HAG appeared no notable rising as gout duration extension. HAG was found in 5.03% (8/159) of joints of the patients who had less than one year gout course, and it was 6.36% (7/110) in the patients with more than 15 years of gout course (Table 5.1).
In the 35 patients at early stage (gout course was less than 1 year), 28 patients came to clinic at their first gout attack and the affected joints were MTP1 (17), ankles (6), knee (1), acrotarsium (2) and hand joints (2). In the 17 affected MTP1 joints, 8 (47.06%) joints were detected MSU crystal deposition (3 DCS, 3 HAG, 2 Tophi, 1 DCS+Tophi) (Table5.2).
Correlation of joint MSU crystal deposition with nephrolithiasis
Gout patients were reported prone to have nephrolithiasis, acute renal colic or hematuria although it is difficult to determine the type of the crystal in kidney. In this study, we further analyzed the US data of kidney. Nephrolithiasis was defined as US signs of calculus or crystal deposition in kidney. We found that nephrolithiasis was detected in 20.30% (41/202) of gout patients and 4.65% (2/43) of hyperuricemia patients, indicating nephrolithiasis occurred in more gout patients than in hyperuricemia patients. The findings also showed that nephrolithiasis was remarkably relevant to MSU crystal deposition in joints in gout patients (p<0.05) (Table 6).