Mapping Dermatology Life Quality Index with EQ-5D health utility index score in Chinese patients with moderate to severe psoriasis

Psoriasis is a chronic autoimmune skin condition marked by red, inflamed and scaly patches [1]. When psoriasis reaches moderate to severe levels, it extends beyond physical discomfort, impacting emotional health, social interactions and overall quality of life [2]. Treatment response in patients with moderate to severe psoriasis (msPsO) can be assessed through various clinical measures and patient-reported outcomes, such as the Dermatology Life Quality Index (DLQI), which evaluates the impact of psoriasis on a patient’s quality of life. Improvements in DLQI scores reflect better treatment response and reductions in psoriasis-related burdens on daily activities, work, relationships and emotional well-being [3]. However, DLQI is a dermatology-specific instrument, and not a generic tool for assessing quality of life in health economics research, which is vital for evaluating the cost–effectiveness of treatments. To address this, mapping DLQI scores to a generic quality-of-life measure like the EuroQol 5-Dimension (EQ-5D) questionnaire is crucial for economic evaluation of treatment in patients with msPsO.

Existing evidence shows a moderate to strong correlation between DLQI and EQ-5D utility values in patients with psoriasis [4–6]. Various regression models, such as linear, logistic and Tobit, have been used to map DLQI to EQ-5D utility index scores [5–8], however, no single mapping function has gained universal acceptance. The relationship between DLQI and EQ-5D may also vary across populations due to cultural, healthcare and socioeconomic differences. Additionally mapping studies from other countries may not fully apply to Chinese populations, given differences in healthcare systems and quality of life perceptions. Unlike DLQI, EQ-5D is not routinely used in China to assess psoriasis severity or treatment response, therefore a dedicated mapping study could help bridge the gap in utility data for Chinese patients with psoriasis, particularly those with moderate to severe disease – who are a key consideration for treatment reimbursement in China.

This study is a retrospective observational analysis that leverages existing psoriasis patient follow-up data from the Department of Dermatology, Xiangya Hospital of Central South University in Changsha, China. Since 2014, the department has routinely collected patient characteristics (including disease severity) and treatment information from all visiting patients with psoriasis. In August 2023, the EuroQol 5-Dimension 5-Level (EQ-5D-5L) tool was added to the routine assessment for quality of life in psoriasis patients. Thus, the patients with psoriasis who visit this clinic allow researchers a unique opportunity to conduct this study to map DLQI with EQ-5D-5L utility index scores among Chinese patients with msPsO. The protocol of this study was prepared for the ethics review but not published. This study was approved by the ethics review committee of Xiangya Hospital. This study did not involve patients or the public in the design, or conduct, or reporting, or dissemination plans of our research due to its retrospective nature.

This study identified 561 patients visiting the study site during the defined patient enrollment period. Overall, 287 patients met both inclusion and exclusion criteria and were randomly split into two groups to create the training set (n = 231) and testing set (n = 56). The patient identification process is illustrated in Figure 1. The two patient sets had well balanced patient characteristics for demographics, disease severity, skin lesion areas and quality of life (Table 1).

This study aimed to develop and validate a mapping function to convert DLQI scores into EQ-5D utility index scores for Chinese patients with msPsO. The findings of this study not only reinforce the feasibility of this mapping technique but also highlight the strong negative correlation between DLQI and EQ-5D-5L, indicating that DLQI can be a valuable surrogate for health utility measures in patients with psoriasis when EQ-5D-5L data are unavailable.

The primary result of the study demonstrated a significant and strong negative correlation between DLQI and EQ-5D-5L utility index scores (correlation coefficient: -0.645, p < 0.001). This finding is consistent with the hypothesis that as psoriasis has a more detrimental impact on dermatology-specific quality of life (higher DLQI scores), the general health-related quality of life (as measured by EQ-5D-5L) declines. The DLQI is particularly focused on the specific ways psoriasis affects a patient’s life, including symptoms, daily activities and emotional well-being [12]. Given this strong correlation, the results suggest that DLQI, although originally designed as a dermatology-specific tool, captures the broader impacts of the disease that are also reflected in generic health utility measures like EQ-5D. The detailed correlation analyses between individual DLQI items and the EQ-5D-5L utility index score further support the robustness of this relationship. For example, symptoms, feelings, daily activities and social interactions exhibited moderate but significant correlations with EQ-5D-5L scores, indicating that these aspects of psoriasis particularly affect patients’ overall health-related quality of life. This suggests that the impact of psoriasis is not limited to visible skin lesions but extends deeper into a patient’s psychological and social functioning, serving as an observation that could inform both clinical care and health economic evaluations.

The study’s development and validation of predictive models for estimating EQ-5D-5L utility index scores from DLQI data yielded a range of results, with the OLS model based solely on the DLQI total score performing best. This model had the lowest RMSE (0.122) and MAE (0.076), indicating that it was the most accurate in predicting EQ-5D-5L scores. This is an important result for health economics because it shows that even a relatively simple model using only the DLQI total score can provide highly accurate estimates of health utility values. In practice, this means that healthcare providers and policymakers can confidently use DLQI data to estimate utility scores, thus facilitating the inclusion of psoriasis treatments in economic evaluations where EQ-5D-5L data may not be available. The ability to map DLQI to EQ-5D-5L utility values is particularly significant in the context of health economics and policy in China. Psoriasis, especially msPsO, imposes a substantial burden not only on patients but also on the healthcare system [13,14]. Cost-utility analyses, which compare the costs and quality-adjusted life years of different treatments, are crucial for informing decisions about the allocation of healthcare resources, pricing and reimbursement. However, the absence of routine EQ-5D-5L data in Chinese patients with psoriasis has historically made it difficult to incorporate psoriasis-specific quality of life impacts into these economic evaluations. By providing a validated mapping function, this study addresses that gap, enabling more accurate and relevant economic evaluations of psoriasis treatments in China. In China, health technology assessment is increasingly becoming a key element in determining the reimbursement and pricing of medications [15,16]. The mapping function developed in this study may therefore serve as a valuable tool in future health technology assessment analyses, particularly among patients with msPsO, a population that is often considered in treatment reimbursement decisions. As a result, this study's findings have the potential to significantly influence the inclusion of psoriasis treatments in China’s national reimbursement drug list, potentially increasing access to more effective therapies for patients.

One of the major strengths of this study is its utilization of a real-world dataset from the Xiangya Hospital psoriasis follow-up database. By focusing on a real-world clinical setting and a diverse patient population, the study’s findings are both highly relevant and generalizable to the broader population of patients with psoriasis in China. Furthermore, the study’s robust methodological approach strengthens its findings. The use of multiple regression models (OLS, Tobit and generalized linear model) allowed for a thorough exploration of the relationship between DLQI and EQ-5D-5L. The validation process using a separate testing dataset demonstrated that the OLS model with DLQI total score as the only independent variable was both accurate and reliable, making it a practical tool for health economics research.

Despite its strengths, this study also has limitations. One limitation is its cross-sectional design, which only captures the relationship between DLQI and EQ-5D-5L at a single time point. Psoriasis is a chronic condition, and patients’ disease severity and quality of life can fluctuate over time, particularly in response to treatment. Longitudinal studies that track these changes would provide more nuanced insights into how DLQI and EQ-5D-5L scores change together over the course of treatment. Additionally, while the exclusion of patients previously treated with biologics and patients with psoriatic arthritis and other autoimmune diseases helped reduce confounding factors, it also limits the generalizability of the results to patients with psoriasis who have comorbid conditions, which represents a significant portion of the psoriasis population. In addition, exclusion of the patients without DLQI or PASI data could further reduce the generalizability of the developed mapping models. Another limitation is that this study focused exclusively on the patients visiting one hospital setting, which means the results may not be directly applicable to other hospital settings. Future studies should validate the mapping function in other settings and explore whether the function is applicable to Chinese patients irrespective of their social economics status, disease severity, treatment response and comorbidities.

This study successfully developed a robust and validated mapping function to convert DLQI scores into EQ-5D utility values for Chinese patients with msPsO visiting a large tertiary hospital. The strong negative correlation between DLQI and EQ-5D underscores the relevance of DLQI in reflecting not only dermatology-specific but also broader health-related quality of life impacts. By bridging the gap between dermatology-specific and generic QoL measures, this study provides a valuable tool for healthcare providers, policymakers and researchers seeking to improve the management of msPsO in China.

L Jian, Y Kuang, J Li, W Chen, X Wang, W Li and P Wang formulated the research idea and developed the study protocol. Tingyin Chen developed and implemented EQ-5D-5L electronic data collection tool for this study. L Jian, Y Duan, K Hu and M Zhang conducted the study subject identification and data collection. L Tan and W Chen performed the data analysis with the support from W Li and P Wang. L Jian, Y Kuang, J Li, T Chen, W Chen and X Wang developed the manuscript draft. All authors have critically reviewed the manuscript and approved its submission.

This study was funded by Bristol Myers Squibb, The National Key Research and Development Program of China (2023YFC2508105) and The National Natural Science Foundation of China (82373484).

L Tan and W Chen are the employees of Changsha Normin Medical Technology Ltd, which received funding from Bristol Myers Squibb to conduct this study. X Wang is the employee of Bristol Myers Squibb. The authors have no other competing interests or relevant affiliations with any organization or entity with the subject matter or materials discussed in the manuscript apart from those disclosed.

No funded writing assistance was utilized in the production of this manuscript.

Reviewed and approved by Xiangya Hospital of Central South University (approval #2024060716).

The data that support the findings of this study are available from Xiangya Hospital but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available. Data are however available from the corresponding authors upon reasonable request and with permission of Xiangya Hospital.

This work is licensed under the Attribution-NonCommercial-NoDerivatives 4.0 Unported License. To view a copy of this license, visit https://creativecommons.org/licenses/by-nc-nd/4.0/