Harmonizing measurement of eczema control: mapping scores between the Atopic Dermatitis Control Tool and the Recap of Atopic Eczema instrument.

Background: The Harmonising Outcome Measures for Eczema (HOME) initiative has established a core outcome set for atopic dermatitis (AD) clinical trials, including four core outcome domains: clinician-reported signs, patient-reported symptoms, eczema control and quality of life. For eczema control, the Atopic Dermatitis Control Tool (ADCT) and the Recap of Atopic Eczema (RECAP) were chosen through consensus methods as equivalent instruments.

Objectives: This study aimed to develop equations to map scores between ADCT and RECAP to facilitate inter-measurement comparison and data synthesis.

Methods: Patients with AD completed the HOME core outcome set of instruments, including ADCT, RECAP, Dermatology Life Quality Index series, Peak Pruritus Numerical Rating Scale and Patient-Oriented Eczema Measure, during routine clinic visits. Clinicians assessed disease severity using the Investigator Global Assessment x Body Surface Area measure.

Results: Among 50 participants, ADCT and RECAP were strongly correlated (Pearson's correlation coefficient, r = 0.970). Four mapping models were evaluated: simple linear regression (SLR), SLR without intercept, square root transformation (SRT) and SRT without intercept. While the SRT no intercept model had the lowest root mean square error, it produced nonlinear confidence intervals and risked overfitting. The SLR no intercept model, with high predictive accuracy (R2 = 0.971) and interpretability, was selected as the primary approach. Two equations were derived to convert scores between ADCT and RECAP, enabling standardized comparisons.

Conclusions: This study provides two equations for mapping between ADCT and RECAP, strengthening the HOME outcome measurement set and synthesizing the two measures for clinical and research purposes. Validation with larger, independent cohorts is warranted to confirm these findings.