The burden of subclinical synovitis in gout

Background: Gout is one of the common forms of inflammatory arthritis in the community. It is still under diagnosed and suboptimally managed in the population. The lack of proper outcome tools in the management of gout is one among the many reasons for the inadequate management. Ultrasound (US) in gout could potentially be used as an outcome tool as US is more sensitive than clinical examination for the detection of synovitis.

Aims: This pilot study aimed to assess the burden of subclinical synovitis in acute and in intercritical gout.

Methods: 30 subjects with gout according to American College of Rheumatology/ European League Against Rheumatism criteria were included. Each person was examined twice, once in the acute gout and once in the intercritical visit. At each visit, 52 joints were examined for tender and swollen joint count and for gray-scale (GS) and power Doppler (PD). Patient questionnaires assessing pain, gout severity, function and laboratory testing for uric acid, ESR, CRP, HsCRP were performed.

Results: At the acute visit, the median tender and swollen joint count was one (IQR 1-2). The median joint count per patient with GS and/or PD≥2 was seven (IQR 5-14). The median number of joints with only US detected synovitis without clinical involvement was four (IQR 2-9). At the intercritical visit, the median tender and swollen joint count was zero (IQR 0-0). The median joint count per patient with GS and/or PD≥2 was six (IQR 4-11). The median number of joints with only US detected synovitis without clinical involvement was four (IQR 3-7). There were significantly (p-value <0.001) more joints swollen and tender at the acute visit (median joint count 1 (IQR 1-2) compared with the intercritical visit (median joint count 0 (0-0), but the number of joints with GS or PD signal were not different between the two visits. There was no difference in the patient reported outcomes between the two visits, except in gout pain severity which was significantly greater at the acute visit. Serum uric acid and hsCRP were not different between visits. As expected, ESR and CRP were significantly higher at the acute visit compared with the intercritical visit. When a small subset of patients with serum uric acid level ≤0.36mmol/L at both visits was compared against those with higher serum uric acid, there were no differences in the amount of US detected synovitis, patient reported outcomes and biochemical markers of inflammation between two groups at both visits.

Conclusions: This pilot study establishes the presence of subclinical synovitis in gout at both acute and intercritcal phases. Subclinical synovitis is common both at the acute and in the intercritical phases of gout. The amount of subclinical synvoitis does not significantly decrease with resolution of the acute attack. The long-term implications of untreated subclinical synovitis are not clear. The role of ultrasound in understanding gout, and its clinical utility requires further investigation.