Tophus measurement as an outcome measure in gout: an updated systematic literature review.

OBJECTIVE

To conduct an updated review of methods of tophus measurement in gout and evaluate each method according to the Outcome Measures in Rheumatology (OMERACT) Filter 2.2.

METHODS

A systematic search for methods of tophus assessment from 2010 to 2024 was conducted. Publications before 2010 were identified from a previous review published in 2011. Instruments were assessed according to the OMERACT 2.2, a framework for evaluating three key pillars of measurement instruments: their feasibility, truth, and discrimination.

RESULTS

Ten methods were identified: counting the number of tophi, tape measurement, Vernier callipers, digital photography, ultrasound (US), computed tomography (CT), dual-energy computed tomography (DECT), magnetic resonance imaging (MRI), plain radiography and the Tophus Impact Questionnaire (TIQ-20), a patient-reported outcome measure. Vernier callipers correlated well with other physical measurement techniques, had good to excellent reliability, and demonstrated responsiveness to treatment and discrimination. US and DECT had excellent reliability and showed responsiveness to treatment but have not yet demonstrated a difference in tophus size in a randomized controlled trial (RCT) and have higher cost and training requirements. The TIQ-20 had high feasibility and demonstrated responsiveness, but further research is required regarding its discrimination.

CONCLUSION

There is evidence to support the feasibility, truth and discrimination of Vernier callipers. US, DECT and the TIQ-20 fulfil many aspects of the Filter but have not yet demonstrated a difference between arms of a RCT. Overall, Vernier callipers have evidence for each pillar of the Filter and are a strong candidate for endorsement as an instrument of tophus measurement.