Since psoriasis is associated with substantial impairment in health-related quality of life (HRQoL), this outcome has become an important endpoint in clinical trials and indicator of disease severity in clinical practice. HRQoL can be measured using either generic instruments, such as the EuroQol 5-Dimension 3-Level (EQ-5D-3L), or dermatology-specific HRQoL instruments, such as the Dermatology Life Quality Index (DLQI). While generic HRQoL instruments are typically more extensively validated and allow for cross-disease comparisons, dermatology-specific instruments may have better responsiveness to change, which is important when evaluating the impact of treatment in clinical trials or routine practice. However, little is known about the relative responsiveness of generic versus disease-specific instruments for patients with psoriasis.1,2 In addition, while the recently proposed Dermatology Life Quality Index-Relevant (DLQI-R) scoring modification has been suggested as an approach to reduce bias associated with ‘not relevant’ responses on the traditional DLQI, the responsiveness of this modification has not been thoroughly evaluated.3,4
The purpose of this study was to evaluate the relative responsiveness of the DLQI, DLQI-R, and a generic instrument, the EQ-5D-3L. The DLQI-R scoring modification involves multiplying the traditional DLQI score by a conversion factor that increases with the number of ‘not relevant’ responses. A cross-sectional reanalysis was conducted using data from the Vascular Inflammation in Psoriasis trial (a multi-center clinical trial of patients with moderate to severe psoriasis).5 The changes in DLQI, DLQI-R, and EQ-5D-3L index value and visual analog scale (VAS) scores from baseline to week 12 were compared with changes in Psoriasis Area Severity Index (PASI) scores using Speaman’s rank order correlations. Stieger’s Z was used to evaluate for significant differences between correlation coefficients.6 In addition, standardized response means (SRM) were calculated for the change in DLQI, DLQI-R, and EQ-5D-3L index value and EQ VAS scores from baseline to week 12, which were compared using paired Student’s t-test.1 Statistical analyses were performed using Stata 15 (StataCorp, College Station, TX). This study was approved by Institutional Review Board of the University of Pennsylvania.
Among 93 subjects, the mean improvement in HRQoL from baseline to week 12 was 6.1 (SD 6.7) for the DLQI and 6.6 (SD 7.0) for the DLQI-R. The mean improvement in HRQoL from baseline to week 12 was 0.08 (SD 0.19) and 5.0 (SD 32.2) for the EQ-5D-3L index value and EQ VAS, respectively. Compared to the EQ-5D-3L index values, the DLQI (SRM difference 0.53; 95% CI 0.33-0.73) and DLQI-R (SRM difference 0.57; 95% CI 0.37-0.77) were more responsive. Compared to EQ VAS, the DLQI (SRM difference 0.77; 95% CI 0.49-1.04) and DLQI-R (SRM difference 0.80; 95% CI 0.52-1.08) were more responsive. The DLQI-R was more responsive than the DLQI, approaching statistical significance (SRM difference 0.03, 95% CI 0.00-0.07) (Table 1). Among the subgroup of subjects with at least one ‘not relevant’ response at baseline and week 12 (n=18), the DLQI-R was more responsive than the DLQI (SRM difference 0.19, 95% CI 0.07-0.30). The DLQI (Spearman’s ρ=0.71) had superior correlation with changes in PASI scores compared to the EQ-5D-3L index values (ρ=−0.51, p<0.001) and EQ VAS (ρ=−0.28, p<0.001). The DLQI-R (ρ=0.70) had superior correlation with changes in PASI scores compared to the EQ-5D-3L index values (ρ=−0.51, p<0.001) and EQ VAS (ρ=−0.28, p<0.001), and similar correlation compared to the DLQI (ρ=0.71, p=0.67).
Table 1:
Mean patient reported outcomes and investigator assessment scores at baseline and week 12, including change from baseline to week 12
| Measure | Baseline, mean (SD, range) | Week 12, mean (SD) | Change, mean (SD) | t-statistic (for change) | Standardized Response Mean (95% CI) | Difference compared to DLQI (95% CI) † | Difference compared to DLQI-R (95% CI) ‡ |
|---|---|---|---|---|---|---|---|
| PASI | 18.9 (7.1, 10.7–52.4) | 11.2 (10.9) | −7.7 (10.2) | −7.3 | 0.76 (0.56 to 0.97) | 0.14 (−0.02 to 0.31) | 0.18 (0.02 to 0.34) |
| PGA | 3.3 (0.6, 2–5) | 2.1 (1.1) | −1.2 (1.1) | −10.5 | 1.10 (0.89 to 1.30) | −0.19 (−0.39 to 0.01) | −0.15 (−0.35 to 0.05) |
| DLQI | 12.5 (6.1, 2–28) | 6.6 (6.9) | −6.1 (6.7) | −8.7 | 0.91 (0.70 to 1.12) | - | −0.03 (−0.07 to 0.00) |
| DLQI-R | 13.5 (6.3, 2–28) | 6.9 (7.1) | −6.6 (7.0) | −9.1 | 0.94 (0.74 to 1.15) | 0.03 (0.00 to 0.07) | - |
| EQ-5D-3L IV | 0.76 (0.17, 0.17–1.00) | 0.85 (0.17) | 0.08 (0.19) | 4.3 | 0.38 (0.18 to 0.57) | 0.53 (0.33 to 0.73) | 0.57 (0.37 to 0.77) |
| EQ VAS | 58.4 (30.6, 4–100) | 64.4 (31.7) | 5.0 (32.2) | 1.5 | 0.14 (−0.07 to 0.35) | 0.77 (0.49 to 1.04) | 0.80 (0.52 to 1.08) |
PASI: Psoriasis Area Severity Index; PGA: Psoriasis Global Assessment; DLQI: Dermatology Life Quality Index; DLQI-R: Dermatology Life Quality Index-Relevant (DLQI-R); EQ-5D-3L: EuroQol 5-Dimension 3-Level; IV: Index Value; VAS: Visual Analog Scale.
larger numbers support DLQI more responsive
larger numbers support DLQI-R more responsive
These results highlight that in a cohort of patients being treated for moderate-to-severe psoriasis in the United States, the dermatology-specific DLQI and DLQI-R were more responsive than the generic EQ-5D-3L HRQoL instrument. These findings suggest that in settings where responsiveness is of significant importance, such as when monitoring disease activity in routine clinical practice, dermatology-specific instruments should be preferred over generic measures of HRQoL. In addition, our results demonstrate that the DLQI-R has excellent responsiveness, nearly outperforming the traditional DLQI in this cohort, although this difference may not be clinically meaningful. While additional validation of the DLQI-R is needed in larger populations and other skin diseases, this scoring modification may hold promise as a strategy to help reduce bias introduced by ‘not-relevant’ responses on the DLQI.7 Future studies may also want to evaluate whether there are differences between the DLQI and DLQI-R specifically among the subgroup of patients who respond ‘not-relevant’ to one or more items. However, the DLQI does have several additional weaknesses, such as item bias and disordered response thresholds, and there is a need for continued psychometric research to develop improved dermatology-specific HRQoL instruments to ensure that we can effectively measure this important outcome for patients with skin diseases.8
Acknowledgments
Funding statement: 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.
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.
Footnotes
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 received payment for continuing medical education work related to psoriasis that was supported indirectly by Eli Lilly and Ortho Dermatologics. No other disclosures were reported.
References:
- 1.Wiebe S, Guyatt G, Weaver B, et al. Comparative responsiveness of generic and specific quality-of-life instruments. J Clin Epidemiol 2003; 56:52–60. [DOI] [PubMed] [Google Scholar]
- 2.Shikiar R, Willian MK, Okun MM, et al. The validity and responsiveness of three quality of life measures in the assessment of psoriasis patients: results of a phase II study. Health Qual Life Outcomes 2006; 4:71. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Rencz F, Gulácsi L, Péntek M, et al. Proposal of a new scoring formula for the DLQI in psoriasis. Br J Dermatol 2018. doi: 10.1111/bjd.16927. [DOI] [PubMed] [Google Scholar]
- 4.Rencz F, Brodszky V, Gulácsi L, et al. Time to revise the DLQI scoring in psoriasis treatment guidelines. J Eur Acad Dermatol Venereol JEADV 2019. [DOI] [PubMed] [Google Scholar]
- 5.Mehta NN, Shin DB, Joshi AA, et al. Effect of 2 Psoriasis Treatments on Vascular Inflammation and Novel Inflammatory Cardiovascular Biomarkers: A Randomized Placebo-Controlled Trial. Circ Cardiovasc Imaging 2018; 11:e007394. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6.Lee I, Preacher K. Calculation for the test of the difference between two dependent correlations with one variable in common [WWW Document]. URL http://quantpsy.org [accessed on 6 March 2019].
- 7.Barbieri J, Gelfand JM. Evaluation of the Dermatology Life Quality Index scoring modification, the DLQI-R score, in two independent populations. Br J Dermatol 2018. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Nijsten T Dermatology life quality index: time to move forward. J Invest Dermatol 2012; 132:11–3. [DOI] [PubMed] [Google Scholar]