Establishment and partial validation of a patient skin self-assessment questionnaire in systemic sclerosis

Abstract

To construct a patient self-assessment questionnaire testing whether patients can provide valid information about their skin thickness, tethering and thinness. The questionnaire contained questions about the 17 body areas identical to those investigated in the Modified Rodnan Skin Score (MRSS). The baseline and 1 yr follow-up values of thickening, tethering and thinning were scored on a scale of 0-3, by 131 consecutive patients. The questionnaire was feasible. The test-retest reliability was good, with an intraclass correlation coefficient of 0.5-0.6. The MRSS correlated with the 17-area thickness score (rho = 0.435, P < 0.001). Both the patient-reported thickness and tethering scores and the expert-measured MRSS and tethering scores correlated highly with each other (rho = 0.523, P < 0.001 and rho = 0.637, P < 0.001, respectively). The patient-reported thinness scores did not show any correlation with the examiner-measured skin thickening/tethering. All thickness-related scores were sorted into the same factor by principal component analysis. Conversely, skin thinness scores were sorted into a distinct factor. Skin thickness scores reported by diffuse SSc patients were different from those of the limited SSc cases (P < 0.05). We validated the skin thickness domain of the questionnaire, except the responsiveness. Because of the low mean MRSS of patients in this investigation, the patient self-assessment validation procedure should be repeated with cases exhibiting more extensive skin involvement. Patient-reported and examiner-measured tethering may not be used as independent instruments of skin involvement. The skin thinness domain may contain valuable independent information, therefore it also merits further investigation.