Validity, reliability, and feasibility of durometer measurements of scleroderma skin disease in a multicenter treatment trial

Abstract

Objective: To determine the validity, reliability, and feasibility of durometer measurements of skin hardness as an outcome measure in clinical trials of scleroderma.

Methods: Skin hardness was measured during a multicenter treatment trial for scleroderma using handheld digital durometers with a continuous scale. Skin thickness was measured by modified Rodnan skin score (MRSS). Other outcome data collected included the Scleroderma Health Assessment Questionnaire. In a reliability exercise in advance of the trial, 9 investigators examined the same 5 scleroderma patients by MRSS and durometry.

Results: Forty-three patients with early diffuse cutaneous systemic sclerosis were studied at 11 international centers (mean age 49 years [range 24-76], median disease duration 6.4 months [range 0.3-23], and median baseline MRSS 22 [range 11-38]). The reliability of durometer measurements was excellent, with high interobserver intraclass correlation coefficients (ICCs) (0.82-0.92), and each result was greater than the corresponding skin site ICCs for MRSS (0.54-0.85). Baseline durometer scores correlated well with MRSS (r = 0.69, P < 0.0001), patient self-assessments of skin disease (r = 0.69, P < 0.0001), and Health Assessment Questionnaire (HAQ) disability scores (r = 0.34, P = 0.03). Change in durometer scores correlated with change in MRSS (r = 0.70, P < 0.0001), change in patient self-assessments of skin disease (r = 0.52, P = 0.003), and change in HAQ disability scores (r = 0.42, P = 0.017). The effect size was greater for durometry than for MRSS or patient self-assessment.

Conclusion: Durometer measurements of skin hardness in patients with scleroderma are reliable, simple, accurate, demonstrate good sensitivity to change compared with traditional skin scoring, and reflect patients' self-assessments of their disease. Durometer measurements are valid, objective, and scalable, and should be considered for use as a complementary outcome measure to skin scoring in clinical trials of scleroderma.

Figure 1

Repeated durometer measurements at the right forearm taken at the baseline visit demonstrate no clinically meaningful variation among the 3 repeated measurements. Box plots represent the 25th and 75th percentiles, lines inside the boxes represent the median, and whiskers represent the minimum and maximum values.

Figure 2

Durometer scores within a given skin score ranged widely, indicating durometry may provide a greater dynamic range than the modified Rodnan skin score at baseline. Box plots represent the 25th and 75th percentiles, lines inside the boxes represent the median, and whiskers represent the minimum and maximum values.

Figure 3

A, Correlation between the total (17-site) modified Rodnan skin score (MRSS) and the 6-site total durometer score for subjects at baseline trial visit. B, Correlation between total 6-site durometer scores and patients' self-assessment of their skin disease measured by a visual analog scale (scored 0–100) at baseline trial visit. C, Correlation between total 6-site durometer scores and patients' disability index of the Health Assessment Questionnaire (HAQ) at baseline trial visit, which is included in the Scleroderma Health Assessment Questionnaire.

Figure 4

A, Correlation between the change in the total 6-site durometer score and changes in the total 17-site modified Rodnan skin score (MRSS) during the treatment phase of the trial. B, Correlation between change at month 6 in total 6-site durometer scores and change at month 6 in patients' self-assessment of their skin disease as measured by a visual analog scale (scored 0–100). C, Correlation between total 6-site durometer scores and the patients' disability index of the Health Assessment Questionnaire (HAQ), which is included in the Scleroderma Health Assessment Questionnaire. Both endpoints are measured as the change in score from baseline to month 6.