The statistical challenge of analysing changes in dual energy computed tomography (DECT) urate volumes in people with gout.

BACKGROUND: Dual energy computed tomography (DECT) allows direct visualization of monosodium urate crystal deposition in gout. However, DECT urate volume data are often highly skewed (mostly small volumes with the remainder considerably larger), making statistical analyses challenging in longitudinal research. The aim of this study was to explore the ability of various analysis methods to normalise DECT urate volume data and determine change in DECT urate volumes over time. METHODS: Simulated datasets containing baseline and year 1 DECT urate volumes for 100 people with gout were created from two randomised controlled trials. Five methods were used to transform the DECT urate volume data prior to analysis: log-transformation, Box-Cox transformation, log(X-(min(X)-1)) transformation; inverse hyperbolic sine transformation, and rank order. Linear regression analyses were undertaken to determine the change in DECT urate volume between baseline and year 1. Cohen's d were calculated as a measure of effect size for each data treatment method. These analyses were then tested in a validation clinical trial dataset containing baseline and year 1 DECT urate volumes from 91 people with gout. RESULTS: No data treatment method successfully normalised the distribution of DECT urate volumes. For both simulated and validation data sets, significant reductions in DECT urate volumes were observed between baseline and Year 1 across all data treatment methods and there were no significant differences in Cohen's d effect sizes. CONCLUSIONS: Normalising highly skewed DECT urate volume data is challenging. Adopting commonly used transformation techniques may not significantly improve the ability to determine differences in measures of central tendency when comparing the change in DECT urate volumes over time.

Intensive Serum Urate Lowering With Oral Urate-Lowering Therapy for Erosive Gout: A Randomized Double-Blind Controlled Trial.

OBJECTIVE: To determine whether a therapeutic approach of intensive serum urate lowering results in improved bone erosion scores in patients with erosive gout. METHODS: We undertook a 2-year, double-blind randomized controlled trial of 104 participants with erosive gout who were receiving serum urate-lowering therapy orally and who had serum urate levels of ≥0.30 mmoles/liter at baseline. Participants were randomly assigned to either an intensive serum urate target of <0.20 mmoles/liter or a standard target of <0.30 mmoles/liter (considered the standard according to rheumatology guidelines). Oral serum urate-lowering therapy was titrated to target using a standardized protocol (with the maximum approved doses of allopurinol, probenecid, febuxostat, and benzbromarone). The primary end point was the total computed tomography (CT) bone erosion score. Outcome Measures in Rheumatology (OMERACT) gout core outcome domains were secondary end points. RESULTS: Although the serum urate levels were significantly lower in the intensive target group compared to the standard target group over the study period (P = 0.002), fewer participants in the intensive target group achieved the randomized serum urate target level by year 2 (62% versus 83% of patients in the standard target group; P < 0.05). The intensive target group required higher doses of allopurinol (mean ± SD 746 ± 210 mg/day versus 497 ± 186 mg/day; P < 0.001) and received more combination therapy (P = 0.0004) compared to the standard target group. We observed small increases in CT bone erosion scores in both serum urate target groups over 2 years, with no between-group difference (P = 0.20). OMERACT core outcome domains (gout flares, tophi, pain, patient's global assessment of disease activity, health-related quality of life, and activity limitation) improved in both groups over 2 years, with no between-group differences. Adverse event and serious adverse event rates were similar between the groups. CONCLUSION: Compared to a serum urate target of <0.30 mmoles/liter, more intensive serum urate lowering is difficult to achieve with an oral urate-lowering therapy. Intensive serum urate lowering leads to a high medication burden and does not improve bone erosion scores in patients with erosive gout.