Initial validation of the Burden of Disease in Atopic Eczema instrument, a quality-of-life measure for adult atopic dermatitis

Dear Editor, The Harmonising Outcome Measures for Eczema (HOME) initiative identified quality of life (QoL) as a core outcome domain that should be assessed in all atopic dermatitis (AD) trials.1 However, based on a systematic review of the measurement properties of QoL instruments, HOME could not reach consensus on which QoL instrument should be recommended for adult AD.2,3 In response to the need for a valid QoL instrument, we developed the Burden of Disease in Atopic Eczema (BODE) instrument. BODE was designed to address important aspects of QoL included in well‐established generic QoL measures such as the Short Form‐12, modified for patients with AD.4 The objectives of this study were to test the item performance and internal and construct validity of BODE for the assessment of QoL in adult AD. BODE uses visual analogue scales to measure patient‐reported outcomes. A score from 0 (smallest effect) to 10 (largest effect) is derived for each question by measuring the distance from 0 along the line to the point where the patient marked, dividing that by the length of the line and multiplying by 10. BODE includes 10 items assessing physical comfort, social comfort, self‐care, work, volunteer and home care, concentration, emotional health, intimacy and sleep. A pilot version of BODE was administered to participants at two U.S. tertiary care dermatology centres: Rhode Island Hospital and Oregon Health and Science University (OHSU). Inclusion criteria were AD diagnosed by a board‐certified dermatologist, age ≥ 18 years and English speaking. After providing informed consent, each participant completed the BODE along with the Dermatology Life Quality Index (DLQI) and Skindex‐16 – two QoL assessments that are commonly used in AD trials.5,6 At OHSU, a dermatologist additionally performed two assessments of AD severity: an investigator's global assessment (IGA) and the Eczema Area and Severity Index (EASI).7 Sixty‐six participants completed the survey, 29 male and 37 female, with a mean ± SD age of 43·2 ± 15·7 years. Median DLQI, Skindex‐16, EASI and IGA scores are available from the authors. We first performed exploratory factor analysis (EFA) to explore the underlying constructs, subdomains (and subscales) and factors of the BODE and to refine the scale preliminarily to include high‐performance items only. Confirmatory factor analysis (CFA) was then performed to validate the construct(s) and subscales, and to refine the subscale further to include high‐information items only. We adopted a strict item selection criterion so that only items with high information (i.e. factor loadings > 0·6) would be retained in the final scale. The EFA results for BODE suggested the presence of two highly correlated (r = 0·80) yet unique constructs/subdomains that best explain the observed item response patterns (total variance explained = 70%). The two subdomains identified can be roughly categorized into ‘sense of well‐being’ and ‘functional independence’. CFA was used to validate the two subdomains, with all items showing statistically significant strong factor loadings on their respective subdomains (all loadings > 0·6, P < 0·001; all data available by contacting the authors). This indicated high information content. All 10 items met the selection criterion and were therefore retained. To assess internal consistency, Cronbach's α was calculated for the subdomains of sense of well‐being (0·91) and functional independence (0·82), and the overall BODE (0·92). This demonstrated excellent overall internal consistency and very good‐to‐excellent subscale internal consistency. Of the QoL assessments reviewed by Heinl et al. for HOME, only the QoLIAD (Quality of Life Index for Atopic Dermatitis) had similar internal consistency.8 We hypothesized that BODE would correlate strongly with DLQI and Skindex‐16 and moderately with IGA and EASI. Correlation analyses show that BODE scores are strongly correlated with DLQI (Pearson's correlation coefficient r = 0·76, P < 0·001) and Skindex‐16 (r = 0·84, P < 0·001). Correlations were significant but not as strong with measures of severity of the signs of AD (IGA: r = 0·40, P = 0·005; EASI: r = 0·45, P = 0·001). The limitations of this study include the small sample size; replication in larger samples and more heterogeneous populations is needed. Development of the instrument would have been strengthened by initial qualitative interviews with the patients; nevertheless, the BODE has face validity as its items assess the requisite components of AD‐related QoL identified at the HOME IV meeting, which included patient representatives.2 Other gaps remaining in the validation of BODE include test–retest reliability, responsiveness and interpretability. Our initial validation of the BODE (reformatted to fit on one double‐sided piece of paper and emphasizing the term ‘current’ eczema, Fig. S1; see Supporting Information) with regard to construct validity, internal consistency and item information is promising. No currently available QoL instrument for AD shows strength in all three of these categories.3 Pending further validation, BODE may address the clinical and scientific community's need for a valid QoL measure in AD. Funding sources: This work was supported in part by a research grant from the Eczema Society of Canada. Conflicts of interest: A.M.D. and A.A.Q. are investigators for Regeneron and Sanofi (no compensation). A.M.D. has been a speaker for Astellas Canada (honorarium). A.A.Q. is a consultant for AbbVie, Amgen, Centers for Disease Control and Prevention, Janssen, Merck, Novartis and Pfizer (honoraria donated to charity), and an investigator for Amgen (honorarium donated to charity). Fig S1. Burden of Disease in Atopic Eczema (BODE) instrument.

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