Among patients with gout treated with allopurinol, the number and total volume of monosodium urate (MSU) crystal depositions are higher in individuals with evidence of greater disease severity, more frequent flares and tophi, and higher serum urate (sUA) levels, as detected by dual-energy computed tomography (DECT), according to the results of a prospective study published in Annals of the Rheumatic Diseases.

The researchers sought to evaluate crystal deposits in patients with gout who were treated with stable-dose allopurinol and to investigate the potential clinical determinants of crystal deposition. Patients with gout who received allopurinol ≥300 mg/day for at least 3 months were prospectively recruited from the United States and New Zealand. Approximately 25% of patients with palpable tophi and 50% of patients with sUA levels <6.0 mg/dL were enrolled in the study. MSU crystal deposition was measured bilaterally in the hands and wrists; feet, ankles, and Achilles tendons; and knees. The presence and total volume of crystals were assessed by DECT and were analyzed based on sUA levels and features of gout.

A total of 152 patients with gout were treated with allopurinol ≥300 mg/day for a mean of 5.1 years. Of these participants, 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% in patients with sUA <6.0 mg/dL and no palpable tophi to 90.0% in those with sUA ≥6.0 mg/dL and palpable tophi.


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Total volume of MSU crystal deposition was positively associated with sUA ≥6.0 mg/dL, at least 1 gout flare within the past 3 or 12 months, and palpable tophi. The Patient Global Impression of Disease Activity scores were positively correlated with MSU total crystal volume on day 1 (Spearman correlation coefficient [r] =0.31; P =.0001), whereas the Patient Impression of Disease Control scores were negatively correlated with crystal volume on day 1 (r =–0.25; P =.002).

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The investigators concluded that despite treatment with allopurinol doses ≥300 mg/day for a considerable period of time, DECT imaging demonstrated that a substantial proportion of patients with gout and without palpable tophi continue to exhibit MSU crystal deposits. DECT scans may be beneficial in patients with gout as a means of assessing the need for more intensive urate-lowering therapy.

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Reference

Dalbeth N, Nicolaou S, Baumgartner S, Hu J, Fung M, Choi HK. Presence of monosodium urate crystal deposition by dual-energy CT in patients with gout treated with allopurinol [published online November 16, 2017]. Ann Rheum Dis. doi: 10.1136/annrheumdis-2017-212046