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The European Scleroderma Study Group (EScSG) has recently identified three activity 10 point indices devoted to evaluating disease activity in systemic sclerosis (SSc) (table 1),1 which have been externally validated.2
An activity index must rely on widely used methods.3 The whole series index includes the total skin score (TSS) evaluated according to the scoring method of Kahaleh et al (KTSS).4 Because, at present, the modified Rodnan TSS (mRTSS)5 is the method most widely used to assess skin induration in SSc, we considered that the mRTSS value should be included in the whole series index rather than the original KTSS.
For this purpose, we considered only the group of 152 patients with SSc from our original study (out of the total pool of 290 patients) whose data had been used to construct the initial whole series index—that is, those in whom all the parameters listed in the SSc whole series index had been evaluated.1,6 We followed a procedure similar to that used by Medsger et al,7 when obtaining mRTSS values from the original Rodnan TSSs. However, because both KTSS and mRTSS are based on a three point scale, we assigned a score to each of the 17 areas specified by the modified Rodnan system; this score was drawn from the data gathered for the evaluation of the KTSS. Moreover, we ruled out the values relating to the neck, back, and buttocks, and for the fingers, where the Kahaleh system requires two scores—that is, distal and proximal), we used the higher score.
In the 152 patients with SSc studied the KTSS ranged from 0 to 50 (median 18), while the mRTSS ranged from 0 to 44 (median 14). To identify the mRTSS value to consider in the whole series index, we followed the procedure used in our previous study.1 Therefore, we first identified which mRTSS values were significantly correlated in univariate analysis with our “gold standard” of disease activity (that is, the consensus activity score blindly given on clinical charts by protocol management members), the reliability of which had been demonstrated. All the mRTSS values between 10 and 20 were suitable cut off points (that is, a value from 11 to 21 identified patients with a higher consensus activity score). However, an mRTSS value of 14 performed best in multiple regression analysis with a regression coefficient (0.839) that was as high as the one previously obtained by us using the Kahaleh scoring system.
In conclusion, we propose to modify the original activity index (table 1) by changing the method used to assess the TSS and using a value of mRTSS >14.