Reliability and convergent validity of two outcome instruments for pemphigus

Area of Science:

• Dermatology
• Clinical Trial Methodology
• Autoimmune Blistering Diseases

Background:

• Multicenter controlled trials for pemphigus are hindered by the absence of validated disease activity scoring systems.
• Accurate assessment tools are crucial for evaluating treatment efficacy and disease progression in pemphigus.

Purpose of the Study:

• To evaluate the reliability and convergent validity of the Pemphigus Disease Area Index (PDAI).
• To compare the PDAI with the Autoimmune Bullous Skin Disorder Intensity Score (ABSIS) in assessing pemphigus disease activity.

Main Methods:

• 10 dermatologists assessed 15 pemphigus patients using the PDAI and ABSIS.
• Inter-rater and intra-rater reliability were calculated using intra-class correlation coefficients (ICCs).
• Convergent validity was assessed by correlating PDAI and ABSIS with Physician's Global Assessment (PGA).

Main Results:

• PDAI showed high inter-rater reliability (ICC=0.76) and excellent intra-rater reliability (ICC=0.98).
• PDAI demonstrated superior reliability in assessing skin activity (ICC=0.86) compared to ABSIS (ICC=0.39).
• PDAI correlated more strongly with PGA, indicating better convergent validity.

Conclusions:

• The PDAI is a reproducible and valid instrument for assessing pemphigus disease activity.
• PDAI is recommended for use in multicenter trials due to its reliability and correlation with clinical judgment.
• PDAI captures disease variability more effectively than ABSIS in mild-to-moderate pemphigus.