A MRI Assessment of the Response of Chronic, Occult, Synovial-Based Inflammation of Gout to Serum Urate Lowering Therapy

Objective: We have previously demonstrated the severity of synovitis in patients with inter-critical gout did not correlate with serum urate levels (sUA). The aim of this sub-study was to determine if serum urate lowering therapy can improve this chronic synovitis. Methods: All participants had inter-critical gout and received a 3T MRI with and without gadolinium of their index joint (i.e. the joint most often involved with acute attacks). If the subject had a sUA of ≥ 7.0 mg/dL and evidence of synovial pannus on their MRI, they were eligible for enrollment. All were treated with febuxostat with a target sUA of ≤ 6.0 mg/dL. At month 9, the MRI of the index joint was repeated and compared to baseline. The MRI’s were read by two musculoskeletal radiologists in a blinded fashion. The primary endpoint was to determine if there was significant improvement in the severity of synovial pannus from baseline to month 9. Results: 25/32 subjects completed the protocol. The average sUA and synovial pannus score at screening was 9.3 mg/dL (+/- 1.3 SD) and 3.66 (+/- 1.2 SD), respectively. At month 9, the average sUA decreased to 5.36 mg/dL (+/- 1.4 SD; p < 0.0001), but there was no significant change in the severity of synovial pannus with the average score being 3.42 (+/- 1.3 SD; p = 0.34). The inter-reader agreement between the two radiologists was good (kappa = 0.63). However, a post-hoc analysis using a more quantitative synovial pannus scoring scale suggested a significant decrease. Conclusions: Nine months of serum urate lowering therapy significantly decreases serum urate levels but the effect on the chronic, occult, synovial-based inflammation of gout remains unclear.