Presence of monosodium urate crystal deposition by dual-energy CT in patients with gout treated with allopurinol

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 stabledose allopurinol, and investigated potential clinical determinants for crystal deposition. Methods P atients 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 (< 357 mu mol/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.