Tophus measurement as an outcome measure for clinical trials of chronic gout: progress and research priorities.

Despite the recognition that tophus regression is an important outcome measure in clinical trials of chronic gout, there is no agreed upon method of tophus measurement. A number of methods have been used in clinical trials of chronic gout, from simple physical measurement techniques to more complex advanced imaging methods. This article summarizes methods of tophus measurement and discusses their properties. Physical measurement using Vernier calipers meets most aspects of the Outcome Measures in Rheumatology (OMERACT) filter. Rigorous testing of the complex methods, particularly with respect to reliability and sensitivity to change, is needed to determine the appropriate use of these methods. Further information is also required regarding which method of physical measurement is best for use in future clinical trials. The need to develop and test a patient-reported outcome measure of tophus burden is also highlighted.