Minimal clinically important difference in plain films in RA: Group discussions, conclusions, and recommendations

Analysis of progression of structural damage on an individual patient level in randomized controlled trials provides extra information in addition to the analysis on a group level. A cutoff level is required to define which patients show progression and which patients do not. The objective of the minimal clinically important difference (MCID) module for plain films was to elaborate the various concepts to determine a MCID for plain films, and if possible, to define a MCID for specific scoring methods. The module comprised preconference reading material, a plenary session, small group discussions, and a plenary report of the group sessions, combined with interactive voting. The following conclusions and recommendations were made: the smallest detectable difference (SDD) beyond measurement error is a good starting point to define MCID; SDD is study-specific; SDD should be reported for all radiographic endpoints used in a trial as a quality control; the expert panel approach is a reasonable method to define MCID, but defined in this way MCID may be smaller than current SDD; more research is needed to validate expert panel based MCID in different datasets and with different experts; a predictive, data driven MCID is the ultimate goal, but is not yet available; the SDD can be used as a proxy for MCID until a data driven MCID is available; analysis at the group level (comparison of means or medians) should remain primary in studies that include progression of joint damage as outcome measure; the proportion of patients showing more progression than the SDD is a secondary outcome measure.