## 2 Materials and Methods  
APOLO was a multicenter, observational, cross-sectional, single-visit, primary data collection study. Eligible patients were aged \(\geq\)12 years with a confirmed diagnosis of M2S-AD as per the validated Investigator's Global Assessment scale (vIGA-AD \(\geq\) 3) [38], visiting the reference center either for the first time or after not attending regular follow-up for \(\geq\)2 years. The exclusion criteria included current participation in an interventional trial or the presence of other active dermatological conditions which might confound diagnosis or symptom scores. Patient and/or parental informed consent/assent were obtained, as applicable. Patients were selected consecutively.  
Data were collected as part of common clinical practice, while patient-reported outcomes (PROs) were completed by patients at the start of the visit following assessment of eligibility and before any further clinical assessment(s).  
The primary study objective was to assess the burden of M2S-AD using PROs as applicable to adults for AD-associated QoL via the Dermatology Life Quality Index (DLOI) [39; 40; 41], general health perception via the EuroQol-5 Dimensions-3 Level scale (EQ-5D-3L) [42; 43], eczema severity via the Patient-Oriented Eczema Measure (POEM) [44; 45; 46], itching severity via the Peak Pruritus Numerical Rating Scale (PP-NRS)\({}^{\star}\)[47], Work Productivity and Activity Impairment: General Health questionnaire (WPAI:GH) [48; 49], and sleep disturbance [visual analogue scale (VAS) rating of average sleeplessness the previous 3 nights, ranging from 0 \"No sleeplessness\" to 10 \"worst imaginable sleeplessness\"] [50], as well as pain attributes (weekly frequency, worst intensity in the past week, and causes of pain) [24]. Secondary objectives included the description of patient and disease characteristics, treatment patterns, and AD-related HCRU. Associations of disease severity, itch intensity, sleep disturbance, and pain intensity with QoL (DLQI) were investigated as exploratory objectives. Disease severity was stratified according to the Eczema Area and Severity Index (EASI) [13].  
This study followed the Guidelines for Good Pharmacoepidemiology Practice (GPP) [51], the Strengthening of the Reporting of Observational Studies in Epidemiology statement (STROBE) [52], and the local rules and regulations.  
Sample size estimation was based on the precision of estimates. A sample of 200 patients was considered sufficient for the estimation of qualitative variables at a frequency of 50% where the margin of error is largest, with a half-width of 95% confidence interval <7% using the normal approximation method.  
The normality of continuous variables was examined using the Shapiro-Wilk test. For uniformity purposes, the median (interquartile range; IQR) is the main summary statistic presented for non-normally distributed variables in any of the study (sub)populations. Comparison of continuous variables between two independent groups was performed using the two-sample t-test or the Mann-Whitney U-test. Associations between categorical variables were examined through the chi-squared test. The Kruskal-Wallis test was used to assess the differences in continuous/ordinal variables between the DLQI score categories. The Spearman correlation coefficient (rho) was used to assess the correlation between PROs and DLQI score. The association between DLQI and PP-NRS, sleep disturbance, total EASI, and pain intensity scores was examined with univariate and multivariate linear regression analysis. All statistical tests were two-sided at a 0.05 significance level. Statistical analysis was performed using SAS\({}^{\circledR}\) Version 9.4 (SAS Institute Inc., Cary, NC, USA).