The Reliability, Validity and Responsiveness of Two Disease Scores (BPDAI and ABSIS) for Bullous Pemphigoid: Which One to Use?

A significant obstacle in guiding evidence-based management of bullous pemphigoid (BP) is the lack of a standardised, validated scoring system for the condition. The aim of this study was to evaluate the suitability of the Bullous Pemphigoid Disease Area Index (BPDAI) and the Autoimmune Bullous Skin disorder Intensity Score (ABSIS) as outcome measures for BP in clinical trials. Thirty-two BP patients were repeatedly assessed over 4 years using Physician Global Assessment (PGA), anti-BP180 ELISA titres, BPDAI, ABSIS, BPDAI-Pruritus, Autoimmune Bullous Disease Quality of Life (ABQOL) and Treatment of Autoimmune Bullous Disease Quality of Life (TABQOL) questionnaires. The reliability, validity, responsiveness, and minimal clinically important differences (MCIDs) were calculated. For inter-rater reliability, the intra-class correlation coefficients (95% CI) were: BPDAI 0.957 (0.901-0.982) and ABSIS 0.881 (0.736-0.949). Compared to ABSIS, BPDAI was better correlated with PGA (r = 0.875, p < 0.001), BPDAI-Pruritus (r=0.632, p = 0.004), ABQOL (r = 0.521, p = 0.011) and TABQOL (r=0.538, p = 0.008). MCIDs for BPDAI were 4-points for assessing clinical improvement and 3-points for deterioration. ABSIS demonstrated less responsiveness with MCIDs at 8.6-points for improvement and 4-points for deterioration. These results indicate that BPDAI demonstrated excellent reliability, validity and responsiveness, while ABSIS had moderate to good reliability, validity and responsiveness.