title: Lack of change in urate deposition by dual-energy computed tomography among clinically stable patients with long-standing tophaceous gout: a prospective longitudinal study.
abstract: BACKGROUND
  Dual-energy computed tomography (DECT) has potential for monitoring urate deposition in patients with gout. The aim of this prospective longitudinal study was to analyse measurement error of DECT urate volume measurement in clinically stable patients with tophaceous gout.
  
  
  METHODS
  Seventy-three patients with tophaceous gout on stable therapy attended study visits at baseline and twelve months. All patients had a comprehensive clinical assessment including serum urate testing and DECT scanning of both feet. Two readers analysed the DECT scans for the total urate volume in both feet. Analysis included inter-reader intraclass correlation coefficients (ICCs) and limits of agreement, and calculation of the smallest detectable change.
  
  
  RESULTS
  Mean (standard deviation) serum urate concentration over the study period was 0.38 (0.09) mmol/L. Urate-lowering therapy was prescribed in 70 (96%) patients. The median (interquartile range) baseline DECT urate volume was 0.49 (0.16, 2.18) cm(3), and change in DECT urate volume was -0.01 (-0.40, 0.28) cm(3). Inter-reader ICCs were 1.00 for baseline DECT volumes and 0.93 for change values. Inter-reader bias (standard deviation) for baseline volumes was -0.18 (0.63) cm(3) and for change was -0.10 (0.93) cm(3). The smallest detectable change was 0.91 cm3. There were 47 (64%) patients with baseline DECT urate volumes <0.91 cm(3). Higher serum urate concentrations were observed in patients with increased DECT urate volumes above the smallest detectable change (P = 0.006). However, a relationship between changes in DECT urate volumes and serum urate concentrations was not observed in the entire group.
  
  
  CONCLUSIONS
  In patients with tophaceous gout on stable conventional urate-lowering therapy the measurement error for DECT urate volume assessment is substantially greater than the median baseline DECT volume. Analysis of patients commencing or intensifying urate-lowering therapy should clarify the optimal use of DECT as a potential outcome measure in studies of chronic gout.
authors.forename: Ashwin
authors.initials: A
authors.lastname: Rajan
authors.forename: Opetaia
authors.initials: O
authors.lastname: Aati
authors.forename: Ramanamma
authors.initials: R
authors.lastname: Kalluru
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Gamble
authors.forename: Anne
authors.initials: A
authors.lastname: Horne
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Doyle
authors.forename: Fiona M
authors.initials: FM
authors.lastname: McQueen
authors.forename: Nicola
authors.initials: N
authors.lastname: Dalbeth
mesh_terms: D000368:Aged; D000493:Allopurinol / Q000627:therapeutic use; D005260:Female; D005528:Foot / Q000000981:diagnostic imaging / Q000473:pathology; D006073:Gout / Q000097:blood / Q000000981:diagnostic imaging* / Q000188:drug therapy*; D006074:Gout Suppressants / Q000627:therapeutic use; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014527:Uric Acid / Q000032:analysis* / Q000097:blood
chemical_list: D006074:Gout Suppressants; D014527:Uric Acid; D000493:Allopurinol