Establishing minimal clinically important differences for the Pemphigus Disease Area Index.

BACKGROUND

Pemphigus is a rare autoimmune blistering disease with potentially life-threatening consequences. Establishing minimal clinically important differences (MCIDs) for disease severity scores like the Pemphigus Disease Area Index (PDAI) is crucial for assessing treatment efficacy.

OBJECTIVES

To calculate MCIDs for both improvement and deterioration in PDAI scores in patients with pemphigus vulgaris (PV) and pemphigus foliaceus (PF), using the anchor-based method.

METHODS

A total of 41 patients with pemphigus were recruited, with 35 meeting the MCID analysis criteria. The anchor-based method was used to calculate MCIDs for PDAI scores against the 15-point Likert scale and the Physician Global Assessment visual analogue scale (PGA-VAS) anchors. Receiver operating characteristic curves were employed to determine optimal MCID cutpoints with the highest Youden Index (J). The 15-point Likert scale scores the change in disease severity spanning from -7 to +7, designed to quantify the extent of disease improvement/deterioration since the preceding visit.

RESULTS

The MCID for improvement in PDAI activity scores was 2.65 points using the 15-point Likert scale (78.7% correct classification; sensitivity 75.9%; specificity 73.5%) and 2.5 points using the PGA-VAS as the anchor (78.0% correct classification; sensitivity 84.4%; specificity 68.2%). Given the slightly higher correct classification rate using the 15-point Likert scale anchor, the MCID of 2.65 points was selected for PDAI activity score improvement. In contrast, the MCID for deterioration consistently remained at 2.5 points for the 15-point Likert scale anchor (81.0% correct classification; sensitivity 72.7%; specificity 81.0%) and 2.5 points for the PGA-VAS anchor (70.9% correct classification; sensitivity 69.6%; specificity 76.9%).

CONCLUSIONS

This study marks the inaugural attempt at MCID determination for PDAI scores in pemphigus, filling a critical knowledge gap. The study's calculated MCIDs provide essential benchmarks for clinical trials, treatment evaluation and research design optimization. Future studies should explore international collaborations, to examine potential cross-cultural variations in MCIDs.