1. ¹Department of Dermatology, University of Pennsylvania, Philadelphia, Philadelphia, USA
2. ²Department of Dermatology, St George Hospital, University of NSW, Sydney, Australia
3. ³Department of Dermatology, New York University Medical Center, New York, New York, USA
4. ⁴Division of Dermatology, Department of Dermatology, Duke Medical Center, Durham, North Carolina, USA
5. ⁵Department of Dermatology, University Hospitals of Cleveland, Case Western Medical Center, Cleveland, Ohio, USA
6. ⁶Division of Dermatology, Department of Dermatology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
7. ⁷Department of Dermatology, University of North Carolina, Chapel Hill, North Carolina, USA
8. ⁸Department of Dermatology, The Keck School of Medicine, University of Southern California, Los Angeles, USA
9. ⁹Department of Biostatistics and Epidemiology, University of Pennsylvania, Philadelphia, Philadelphia, USA
10. ¹⁰Department of Dermatology, Philadelphia V.A. Medical Center, Philadelphia, Philadelphia, USA

Correspondence: Dr Victoria P. Werth, Department of Dermatology, University of Pennsylvania, 2, Rhodes Pavilion, 3600 Spruce Street, Philadelphia, Philadelphia 19119, USA. E-mail: werth@mail.med.upenn.edu

Received 3 September 2008; Revised 22 January 2009; Accepted 5 February 2009; Published online 9 April 2009.

Abstract

A major obstacle in performing multicenter controlled trials for pemphigus is the lack of a validated disease activity scoring system. Here, we assess the reliability and convergent validity of the PDAI (pemphigus disease area index). A group of 10 dermatologists scored 15 patients with pemphigus to estimate the inter- and intra-rater reliability of the PDAI and the recently described ABSIS (autoimmune bullous skin disorder intensity score) instrument. To assess convergent validity, these tools were also correlated with the Physician's Global Assessment (PGA). Reliability studies demonstrated an intra-class correlation coefficient (ICC) for inter-rater reliability of 0.76 (95% confirdence interval (CI)=0.61–0.91) for the PDAI and 0.77 (0.63–0.91) for the ABSIS. The tools differed most in reliability of assessing skin activity, with an ICC of 0.39 (0.17–0.60) for the ABSIS and 0.86 (0.76–0.95) for the PDAI. Intra-rater test-retest reliability demonstrated an ICC of 0.98 (0.96–1.0) for the PDAI and 0.80 (0.65–0.96) for the ABSIS. The PDAI also correlated more closely with the PGA. We conclude that the PDAI is more reproducible and correlates better with physician impression of extent. Subset analysis suggests that for this population of mild-to-moderate disease activity, the PDAI captures more variability in cutaneous disease than the ABSIS.