Skin thickness score in systemic sclerosis: an assessment of interobserver variability in 3 independent studies.

Objective: Using data from 3 independent studies, to quantify the interobserver reliability of semi-quantitative skin scoring methods (the original and the modified Rodnan skin thickness scores) used to assess the degree and extent of cutaneous thickening in systemic sclerosis (SSc).

Method: Interobserver variability of the original Rodnan skin thickness score method (cutaneous thickness assessed in 26 body surface areas using a 0-4 scale) was evaluated in one study. The modified Rodnan method (cutaneous thickness assessed in 17 body surface areas using a 0-3 scale) was evaluated in 2 studies. In all 3 studies, each patient's skin thickness was assessed by 6 or 7 observers in a blinded fashion.

Results: The overall within patient standard deviations were not statistically different in all 3 studies (5.4, 4.6 and 4.6) irrespective of the overall mean skin thickness scores (26.6, 18.3 and 17.7). With the original Rodnan technique, the within patient standard deviation tended to be higher in patients with higher skin thickness scores. In the 2 studies which used the modified technique, no significant differences in within patient standard deviation were noted between high and low skin thickness scores.

Conclusions: Three independent studies demonstrate that the Rodnan skin thickness scoring techniques are reproducible among different observers (the within patient standard deviation being consistently about 5 units). Our data provide valuable information needed for sample size calculations for SSc trials in which skin thickness score is an outcome variable.