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. 2024 Oct 17;191(5):823-831.
doi: 10.1093/bjd/ljae283.

Establishing minimal clinically important differences for the Pemphigus Disease Area Index

Henry Tseng  1   2 , Corey Stone  1   2 , Boaz Shulruf  2 , Dédée F Murrell  1   2
Affiliations

Establishing minimal clinically important differences for the Pemphigus Disease Area Index

Henry Tseng et al. Br J Dermatol. .

Abstract

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.

Plain language summary

Pemphigus is a rare and severe skin disease that causes painful blisters on the skin and mucous membranes. It affects about 1 to 5 people per million worldwide. In pemphigus, the immune system attacks the skin by mistake, leading to blisters that can be life-threatening if they get infected. In the past, the main treatment was steroids, which are effective, but they can have many side effects. Newer treatment options (with drugs such as rituximab) have reduced the risk of complications and relapses. The progress made in treating pemphigus has come from carrying out well-designed research studies. One important tool used to study pemphigus is the ‘Pemphigus Disease Area Index’ (or ‘PDAI’ for short). The PDAI helps doctors measure the severity of the disease. However, it has limitations and may not show small improvements that still matter to patients. This is where the ‘minimal clinically important difference’ (or ‘MCID’ for short) comes in. The MCID tells us how much change in PDAI scores is meaningful for patients. To date, there have been no studies published on MCIDs for the PDAI. This study, from Sydney, Australia, aimed to determine MCIDs for the PDAI. We studied 41 patients with pemphigus, 35 of whom were included in MCID analysis. The findings showed that a decrease of 2.65 points in PDAI scores means the disease is getting better. An increase of 2.5 points shows that the disease is getting worse. This information can help doctors and researchers understand if treatments are working and how they affect patients. Overall, our study findings are an important step towards improving care and treatments for people living with pemphigus.

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Conflict of interest statement

Conflicts of interest D.F.M. was a co-investigator/co-creator of the Pemphigus Disease Area Index. The other authors declare no conflicts of interest.

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