Durometry for the Assessment of Skin Disease in Systemic Sclerosis EUGENE Y. KISSIN, AILEEN M. SCHILLER, RONDI B. GELBARD, JENNIFER J. ANDERSON, VINCENT FALANGA, ROBERT W. SIMMS, JOSEPH H. KORN, AND PETER A. MERKEL Objective. To examine the validity of a durometer to objectively measure skin hardness in systemic sclerosis (SSc), and to compare digital durometry with the modified Rodnan skin score (MRSS) and ultrasonography. Methods. Patients with SSc and healthy controls underwent durometry measurements in 3 assessments: a Latin square experiment to establish durometry’s intra- and interobserver reliability compared with skin scoring (5 SSc, 1 control); a longitudinal cohort to assess sensitivity to change in skin hardness (13 SSc, 5 controls); and an ultrasound cohort to evaluate correlation between durometry, ultrasound-measured skin thickness, and clinical skin scoring (30 SSc, 12 controls). Results. Intraobserver reproducibility was higher for durometry than for clinical skin scoring (intraclass correlation coefficient [ICC] 0.97 versus 0.85), whereas interobserver reproducibility was similar (0.75 versus 0.73). Interobserver reproducibility of durometry was good for all body areas (ICC 0.61– 0.85), but for skin scoring it was moderate in the legs (0.51) and poor in the abdomen (0.08), feet (0.09), and fingers (0.27). Durometry scores correlated with clinical skin scores (Latin square: r  0.44, P  0.03; longitudinal cohort: r  0.81, P < 0.001) and ultrasound-measured skin thickness (hands: r  0.58, forearms: r  0.63, upper arms: r  0.40; P < 0.001 for all). Uninvolved skin in patients with SSc was harder than skin from controls (mean  SD 23  7 durometer units [DU] versus 19  6 DU; P < 0.0001). Finally, there was a strong correlation between change in MRSS and change in durometry score (r  0.77, P  0.002). Conclusion. Durometer-measured skin hardness correlates well with MRSS and ultrasound-measured skin thickness, provides greater reliability than MRSS, and is sensitive to changes in skin hardness over time. Durometry should be considered for use in clinical therapeutic SSc trials. KEY WORDS. Systemic sclerosis; Scleroderma; Durometry; Skin score; Ultrasound. INTRODUCTION Systemic sclerosis (SSc; scleroderma) is a multisystem disease characterized by cutaneous and visceral fibrosis. Skin disease is both a disabling feature of SSc and a pre- dictor of visceral involvement and increased mortality (1,2); improvement in skin disease correlates with im- proved survival (3). After an initial period of induration, the dermis becomes infiltrated with collagen and becomes both harder and thicker. Additionally, subdermal connec- tive tissue sclerosis leads to dermal tethering and limited skin mobility (4). Skin involvement in SSc is currently measured semi- quantitatively using the modified Rodnan skin score (MRSS), a summation of physical examination ratings over 17 skin sites (1,5). Skin scores from the forearm correlate with weight of skin punch biopsy scores (5). Limitations of MRSS include the potential for observer bias; intra- and interobserver variability of 12% and 25%, respectively (6,7); the need for investigator training (8); varying degrees of examiner experience (8); and uncertainty about the sen- Supported by a General Clinical Research Center grant (M01-RRO-00533) from the NIH/National Center for Re- search Resources and a Multidisciplinary Clinical Research Center grant (P60-AR-47785) from the NIH/National Insti- tute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS). Dr. Kissin’s work was supported by the NIH Loan Repayment Program. Dr. Merkel is recipient of a Mid-Ca- reer Development Award in Clinical Investigation (K24-AR- 2224-01A1) from the NIH/NIAMS and a Clinical Research grant from The Scleroderma Foundation. Eugene Y. Kissin, MD, Aileen M. Schiller, Rondi B. Gelbard, Jennifer J. Anderson, PhD, Vincent Falanga, MD, Robert W. Simms, MD, Joseph H. Korn, MD, Peter A. Merkel, MD, MPH: Boston University School of Medicine, Boston, Massachusetts. Address correspondence to Peter A. Merkel, MD, MPH, Arthritis Center, E5, Boston University School of Medicine, 715 Albany Street, Boston, MA 02118. E-mail: pmerkel@ bu.edu. Submitted for publication August 10, 2005; accepted in revised form December 9, 2005. Arthritis & Rheumatism (Arthritis Care & Research) Vol. 55, No. 4, August 15, 2006, pp 603– 609 DOI 10.1002/art.22093 © 2006, American College of Rheumatology ORIGINAL ARTICLE 603