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Establishing minimal clinically important differences for the Pemphigus Disease Area Index
Henry Tseng1,2, Corey Stone1,2, Boaz Shulruf2
1Department of Dermatology, St George Hospital, Sydney, NSW, Australia.
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.
