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Extended report
Presence of monosodium urate crystal deposition by dual-energy CT in patients with gout treated with allopurinol
  1. Nicola Dalbeth1,
  2. Savvas Nicolaou2,
  3. Scott Baumgartner3,
  4. Jia Hu3,
  5. Maple Fung3,
  6. Hyon K Choi4
  1. 1 Department of Medicine, University of Auckland, Auckland, New Zealand
  2. 2 Department of Radiology, Vancouver General Hospital and University of British Columbia, Vancouver, British Columbia, Canada
  3. 3 Formerly Ardea Biosciences, Inc., San Diego, California, USA
  4. 4 Department of Rheumatology, Harvard Medical School and Massachusetts General Hospital, Boston, Massachusetts, USA
  1. Correspondence to Dr Nicola Dalbeth, Department of Medicine, University of Auckland, Auckland 1023, New Zealand; n.dalbeth{at}


Objective Dual-energy CT (DECT) detects and quantifies monosodium urate (MSU) crystal deposition with high precision. This DECT study assessed crystal deposition in patients with gout treated with stable-dose allopurinol, and investigated potential clinical determinants for crystal deposition.

Methods Patients with gout treated with allopurinol ≥300 mg daily for at least 3 months were prospectively recruited from the USA and New Zealand, using monitored enrolment to include approximately 25% patients with palpable tophi and approximately 50% with serum urate (sUA) levels <6.0 mg/dL (<357µmol/L). MSU crystal deposition was measured in the hands/wrists, feet/ankles/Achilles and knees bilaterally. The presence and total volume of crystals were assessed by DECT and analysed according to sUA levels and gout characteristics.

Results Among 152 patients receiving allopurinol ≥300 mg/day for 5.1 years on average, 69.1% had crystal deposition on DECT, with a median total crystal volume of 0.16 cm3 (range: 0.01–19.53 cm3). The prevalence of crystal deposition ranged from 46.9% among patients with sUA <6.0 mg/dL and no palpable tophi to 90.0% among those with sUA ≥6.0 mg/dL and tophi. Total volume of crystal deposition was positively associated with sUA ≥6.0 mg/dL, gout flares within the past 3 months and tophi. Total volume of crystal deposition correlated positively with Patient Global Impression of Disease Activity scores.

Conclusion A substantial proportion of patients without palpable tophi have MSU crystal deposition, despite receiving allopurinol doses ≥300 mg/day for a considerable duration. Patients with higher sUA and clinical features of severe disease have a higher frequency and greater volume of MSU crystal deposition.

  • gout
  • treatment
  • patient perspective

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  • Handling editor Tore K Kvien

  • Contributors Criterion 1: (a) substantial contributions to study conception and design; and/or (b) substantial contributions to acquisition of data; and/or (c) substantial contributions to analysis and interpretation of data. Criterion 2: drafting the article or revising it critically for important intellectual content. Criterion 3: final approval of the version of the article to be published. ND: 1a, 1b, 1c, 2, 3. SN: 1a, 1b, 1c, 2, 3. SB: 1a, 1b, 2, 3. JH: 1a, 1b, 1c, 2, 3. MF: 1a, 1bb, 1c, 2, 3. HK: 1a, 1b, 1c, 2, 3.

  • Funding This clinical study was funded by AstraZeneca. The study sponsor had a role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; and review and approval of the manuscript. Editorial support for this manuscript was provided by Bill Wolvey of PAREXEL, which was funded by AstraZeneca.

  • Competing interests ND, grant support from AstraZeneca, participated on speaker bureaus for Menarini, AstraZeneca, Takeda and advisory boards for AstraZeneca, Fonterra, Takeda, Pfizer, Cymabay, and Crealta. SN, University of British Columbia has an MRA with Siemens Healthcare. SB, JH and MF, formerly full-time employees of Ardea Biosciences, a member of the AstraZeneca Group. HKC, grant support from AstraZeneca, consulting fees from Takeda and consulting fees from Selecta.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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