Background Chronic hyperuricemia predisposes to deposition of monosodium urate (MSU) crystals in musculoskeletal and other tissues, causing chronic inflammation, acute gout flares, joint damage, and disfiguring tophi. Dual-energy computed tomography (DECT) is a useful imaging tool to detect and quantify MSU crystal deposits.
Objectives This study assessed the evidence of MSU crystal deposition using DECT scanning among gout patients treated with allopurinol and the potential determinants associated with the observed deposits.
Methods The multicenter DECT study recruited patients with gout from the USA and New Zealand who were taking allopurinol at ≥300 mg daily for at least 3 months. MSU crystal deposition was measured using DECT in hands/wrists, knees, and feet/ankles bilaterally. The presence of MSU crystals as well as the total volume of crystals were assessed according to gout characteristics and serum uric acid (sUA) levels.
Results Patients (N=153) were predominately male (92.2%), with mean (SD) age 58.5 (11.4) years, and gout duration 14.9 (10.3) years. sUA was ≥6.0 mg/dL in 49.0% of patients. 81.7% of patients took allopurinol at a stable dose of 300 mg/day and the remainder at >300 mg/day. 69.1% of patients had MSU crystal deposits with a total median crystal volume of 0.16 cm3 (range, 0.01 to 19.53 cm3). Those with sUA ≥6.0 mg/dL and palpable tophi showed the highest prevalence of urate deposits (90%), and those with sUA <6.0 mg/dL and no palpable tophi showed the lowest prevalence (47%). Those who reported a gout flare within the prior 3 months (versus none), were prescribed allopurinol doses >300 mg (versus 300 mg), and had palpable tophi (versus none) had greater deposit volume.
Conclusions Despite a stable dose of allopurinol for more than 3 months, and even with sUA at the target level, a substantial proportion of patients with gout continue to have evidence of MSU crystal deposition by DECT scan. Patients with palpable tophi, sUA levels ≥6.0 mg/dL, and gout flares within the prior 3 months have a greater volume of MSU crystal deposition. These patients may need continuation and/or intensification of their urate-lowering therapy regimen.
Acknowledgements This study was sponsored by Ardea Biosciences/AstraZeneca.
Disclosure of Interest N. Dalbeth Grant/research support from: AstraZeneca, Consultant for: AstraZeneca, Fonterra, Takeda, Pfizer, Cymabay, Crealta, Speakers bureau: Menarini, AstraZeneca, Takeda, S. Nicolaou Grant/research support from: Siemens Healthcare, S. Baumgartner Employee of: Ardea Biosciences, Inc, J. Hu Employee of: Ardea Biosciences, Inc, M. Fung Employee of: Ardea Biosciences, Inc, H. Choi: None declared