Minimal clinically important difference in radiological progression of joint damage over 1 year in rheumatoid arthritis: Preliminary results of a validation study with clinical experts

To determine the minimal clinically important difference (MCID) between han d and foot films with a 1 year interval assessed with the Sharp/van der Hei jde or Larsen/Scott scoring method. Progression scores of the 2 methods wer e compared with the opinion of an international expert panel on clinical re levance of radiological joint damage in 4 predefined clinical settings. The expert panel consisted of 3 rheumatologists, who evaluated 46 pairs of han d and foot films, taken with 1 year intervals, of patients with early rheum atoid arthritis, Receiver operating characteristics curves analyzed the acc uracy of different threshold values (progression scores) of the 2 scoring m ethods to detect the presence or absence of clinically important difference , as defined by the expert panel as external criterion. The threshold value with the highest accuracy was subsequently chosen as the score representin g the MCID. Five Sharp/van der Heijde units and 2 Larsen/Scott units were t he best cutoffs, The accompanying sensitivities ranged from 77% to 100% for the Sharp/van der Heijde method and from 73% to 84% for the Larsen/Scott m ethod for the 4 clinical settings, The specificities were between 78% and 8 4% for the Sharp/van der Heijde method and between 74% and 94% for the Lars en/Scott method. The smallest progression score that can be detected apart from interobserver measurement error. the smallest detectable difference (S DD), was equal to or larger than the calculated MCID, 5 Sharp/van der Heijd e units and 6 Larsen/Scott units in our study, if the mean progression scor es of the same 2 observers were used. The SDD is a conservative estimate of the MCID: our panel rated progression at or below this level as clinically significant.