Influence of “Not Relevant” Responses on the Dermatology Life Quality Index (DLQI) for Patients With Psoriasis in the United States

The Dermatology Life Quality Index (DLQI) is a popular health-related quality-of-life measure in dermatology. However, there are concerns that scoring “not relevant” responses as equivalent to “not at all” may bias the DLQI toward underestimating severity of disease, and recent studies of patients with psoriasis in Europe found that those who responded “not relevant” had more severe disease than those who responded “not at all.”^1,2 Given cross-cultural differences in response patterns, the purpose of this study was to evaluate whether a similar association exists for the English-language DLQI administered to patients with psoriasis in the United States.³

A cross-sectional reanalysis was conducted using data from the Dermatology Clinical Effectiveness Research Network.⁴ For items 3 through 10 on the DLQI, overall subjective and objective evaluation of the severity of disease were compared between those who responded “not relevant” and those who responded “not at all.” Subjective severity of disease was assessed using the DLQI, EuroQol Health-Related Quality of Life 5-Dimension 3-Level (EQ-5D-3L) index values, and EQ-5D-3L visual analog scale (VAS) scores. Objective severity of disease was assessed using Psoriasis Area Severity Index (PASI) scores. Differences were evaluated using unpaired t tests and Cohen d was calculated for each comparison. A subgroup analysis was performed in those with DLQI scores greater than 5 to assess for differences in those with moderate to severe psoriasis. This study was approved by the University of Pennsylvania institutional review board.

Among 1733 patients (n = 854 women; mean [SD] age, 49.2 [15.4] years), 24% of respondents (95% CI, 22%-26%) had at least 1 “not relevant” response. Item 6 (sport) and item 9 (sexual relationships) were the most frequent items to have “not relevant” responses (Figure, A). In the subgroup analysis of patients with DLQI scores greater than 5 (n = 532), 37% of respondents (95% CI, 33%-41%) had at least 1 “not relevant” response and the frequency of “not relevant” responses was increased across all items (Figure, B). Compared with those who responded “not at all,” those who responded “not relevant” had worse objective disease severity as reflected by higher PASI scores and worse subjective disease severity as reflected by higher DLQI scores and lower EQ-5D-3L index values and VAS scores (Table). The mean Cohen d values were 0.55 for DLQI scores, 0.23 for PASI scores, 0.53 for EQ-5D-3L index values, and 0.32 for EQ-5D-3L VAS scores.

These data and prior studies suggest the DLQI may underestimate disease severity in patients who respond “not relevant” to 1 or more items.^1,2 In addition, the frequency of “not relevant” responses was increased among those with moderate to severe disease, providing further support that patients who respond “not relevant” to 1 or more items may be doing so to indicate more severe disease. The Cohen d value greater than 0.5 for the DLQI score supports that this effect size is likely to be clinically meaningful. Because a DLQI score of greater than 10 has been used as a definition of severe psoriasis and can influence which patients should receive systemic treatments, this underestimation of disease severity in those who respond “not relevant” to 1 or more items could limit access to care.

Given that the DLQI may underestimate disease severity in those who respond “not relevant” to 1 or more items, alternative scoring strategies should be explored, such as the DQLI-R scoring modification, which adjusts the final score based on the number of “not relevant” responses.⁵ Although additional development and validation are needed, using an alternative scoring system could improve the accuracy of the DLQI without changing the current instrument.⁶ Given the importance of quality of life as a clinical and research outcome, continuing psychometric research is needed to develop and refine the most appropriate instruments to measure this outcome in dermatology.

Corresponding Author: John S. Barbieri, MD, MBA, Perelman Center for Advanced Medicine, 7 South Tower, 3400 Civic Center Blvd, Philadelphia, PA 19104 (john.barbieri@uphs.upenn.edu).

Published Online: April 10, 2019. doi:10.1001/jamadermatol.2018.5655

Author Contributions: Dr Barbieri had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Concept and design: Barbieri.

Acquisition, analysis, or interpretation of data: Both authors.

Drafting of the manuscript: Barbieri.

Critical revision of the manuscript for important intellectual content: Both authors.

Statistical analysis: Barbieri.

Obtained funding: Gelfand.

Supervision: Gelfand.

Conflict of Interest Disclosures: Dr Gelfand reported receiving honoraria for serving as a consultant for Bristol-Myers Squibb, Boehringer Ingelheim, GlaxoSmithKline, Janssen Biologics, Novartis Corp, UCB (data and safety monitoring board), and Pfizer Inc; receiving research grants (to the Trustees of the University of Pennsylvania) from AbbVie, Janssen, Novartis Corp, Sanofi, Celgene, Ortho Dermatologics, and Pfizer Inc; and receiving payment for continuing medical education work related to psoriasis that was supported indirectly by Eli Lilly and Ortho Dermatologics. No other disclosures were reported.

Funding/Support: This study was funded in part through the National Institute of Arthritis and Musculoskeletal and Skin Diseases (grant 1P30AR069589-01). Dr Barbieri is supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases of the National Institutes of Health under award T32-AR-007465 and receives partial salary support through a Pfizer fellowship grant to the Trustees of the University of Pennsylvania.

Role of the Funder/Sponsor: The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.