Validity and reliability of the Japanese version of LupusQoL: Assessment of disease-specific health-related quality of life in systemic lupus erythematosus

Abstract

Objective

To develop a Japanese version of LupusQoL (LupusQoL-JP) and assess its validity and reliability in patients with systemic lupus erythematosus (SLE).

Methods

This study consisted of two independent cross-sectional analyses using data from two different periods at our university clinic: 2011 (initial period, n = 266) and 2015–2018 (second period, n = 133). The English version of the LupusQoL was translated into Japanese and administered to Japanese patients with SLE, alongside other questionnaires, including the Medical Outcomes Study Short Form-36 (SF-36) and the 5-level EuroQoL 5-Dimensions Questionnaire (EQ-5D-5L). Physicians also completed measures such as the Systemic Lupus International Collaborating Clinics/American College of Rheumatology (ACR) Damage Index (SDI) and SLE Disease Activity Index 2000 (SLEDAI-2K), and assessed lupus low disease activity state (LLDAS) attainment.

Results

LupusQoL-JP showed acceptable internal consistency (Cronbach’s α > 0.8). All subscales, except for fatigue, demonstrated good test-retest reliability. The LupusQoL-JP and SF-36 scores were strongly correlated with comparable domains. The LupusQoL-JP subscale scores were moderately to strongly correlated with the EQ-5D-5L index values, while weakly correlated with the SDI and generally not correlated with age, disease duration, prednisolone dosage, or SLEDAI-2K. Some LupusQoL-JP domains were able to differentiate between the LLDAS and non-LLDAS groups.

Conclusion

LupusQoL-JP was successfully translated, adapted, and validated. It demonstrated good concurrent validity with comparable domains of the SF-36 and was independent of SLEDAI-2K. Patients with SLE in LLDAS were partly associated with better disease-specific health-related quality of life, as assessed by LupusQoL-JP.

Keywords

Systemic lupus erythematosus health-related quality of life outcome measures

Introduction

Systemic lupus erythematosus (SLE) is a chronic multisystem autoimmune disease that leads to significant morbidity and a reduced health-related quality of life (HRQoL).¹ Most studies assessing HRQoL in SLE have used generic measures, such as the Medical Outcomes Study Short Form-36 (SF-36) survey, which has been validated across various diseases, including SLE, and is recommended as a preferred measure in SLE.^2–5 We have previously demonstrated the validity and reliability of the SF-36 in Japanese patients with SLE.^6,7

However, a key limitation of using only generic instruments in SLE is their inability to fully capture disease-specific symptoms and concerns,⁵ potentially reducing sensitivity to detect meaningful changes over time. To address this issue, several SLE-specific HRQoL measures have been developed.⁵ Although each tool has its strengths and weaknesses, LupusQoL is the most widely used of these measures. Developed and validated by McElhone et al., LupusQoL is a patient-derived, SLE-specific HRQoL measure that includes domains particularly relevant to patients with SLE, such as fatigue, sleep, body image, and emotional intimacy.^8,9 The original UK version of LupusQoL has been translated into multiple languages and is widely used globally.⁵ Furthermore, the psychometric properties of several translated versions have been validated.^10–22 In this study, we aimed to develop a Japanese version of LupusQoL (LupusQoL-JP) and evaluate its validity and reliability in Japanese patients with SLE.

Materials and methods

Study population

This study consisted of two independent cross-sectional analyses using data from two different periods: 2011 (the initial period) and 2015–2018 (the second period). Some patients were included in both periods. All participants were treated at the Tokyo Women’s Medical University Hospital and met either the 1997 American College of Rheumatology (ACR) modified classification criteria for SLE²³ or the 2012 Systemic Lupus International Collaborating Clinics (SLICC) classification criteria.²⁴ Eligible participants were ≥20 years old and provided informed consent to participate. Participants who were unable to complete the questionnaires independently were excluded. Only native Japanese speakers were enrolled, as the study relied on the Japanese versions of the questionnaires, which nonnative speakers might struggle to fully comprehend. This study was approved by the ethics committee of Tokyo Women’s Medical University (registration numbers 2038 and 3042) and was conducted in accordance with the principles of the Declaration of Helsinki.

Data collection

Patients with SLE completed the Japanese versions of the following HRQoL measures: LupusQoL, SF-36 v.2, 5-level EuroQoL 5-Dimensions Questionnaire (EQ-5D-5L, administered only in the second period), and additional demographic questionnaires detailed below. Simultaneously, medical information, including laboratory data, was collected. Treating physicians, who were blinded to the survey responses, assessed disease activity and damage using the SLE Disease Activity Index 2000 (SLEDAI-2K),^25,26 Physician Global Assessment (PGA),²⁷ and the SLICC/ACR Damage Index (SDI).²⁸ Lupus low disease activity state (LLDAS) attainment was evaluated on a per-visit basis using the definition published by Golder et al.²⁹ Because PGA data were unavailable in the initial period, LLDAS was not assessed for that timeframe. LLDAS was defined as meeting the all of the following conditions: SLEDAI-2K ≤4, excluding major organ activity; absence of new SLEDAI-2K activity compared to the preceding visit; PGA score of ≤1 (scale 0–3); and daily prednisolone dose of ≤7.5 mg, with the use of antimalarials and immunosuppressants permitted.

Development of the LupusQoL-JP

The LupusQoL is a validated SLE-specific, HRQoL instrument consisting of 34 items across 8 domains, namely physical health (8 items, Q1–8), emotional health (6 items, Q20–25), body image (5 items, Q26–30), pain (3 items, Q9–11), planning (3 items, Q12–14), fatigue (4 items, Q31–34), intimate relationships (2 items, Q15–16), and burden to others (3 items, Q17–19).⁸ The original UK English version of LupusQoL was translated, back-translated, and culturally adapted into Japanese using a standard methodology.³⁰ The linguistic validation process began with a harmonized translation performed by two translators working independently. Next, a harmonized translation was provided to a third translator, who translated the text back into English without access to the original version. Both harmonized and English back translations were reviewed by a project manager, survey research expert, and Japanese rheumatologist (YK). The translation was revised as needed. Once approved, a trained bilingual (Japanese and English) interviewer cognitively debriefed the subjects (five native Japanese speakers with SLE residing in Japan, with varying demographic and educational backgrounds) via telephone to assess their ability to paraphrase and comprehend the instructions, questions, and responses to determine the conceptual equivalence and clarity of the translation. Corporate Translations (East Hartford, CT), a life science translation company that is ISO 9001:2008 and EN 15038:2006 certified to provide translation and linguistic validation services and solutions, assisted in these processes.

SF-36

Patients completed the Japanese standard (4-week recall) version of the SF-36 v.2.^30–34 The SF-36 consists of 36 items, categorized into the following eight subscales: physical functioning (PF), role limitations: physical (RP), role limitations: emotional (RE), social functioning (SF), bodily pain (BP), mental health (MH), vitality (VT), and general health (GH). Each subscale is scored from 0 to 100, with higher scores indicating better health status.

EQ-5D-5L

The EQ-5D-5L assesses HRQoL across five dimensions: mobility, self-care, usual activities, pain, and anxiety/depression, and each dimension has five levels.³⁵ The responses converted into a single summary index ranging from 0 to 1, where 0 indicates death and 1 indicates complete health. The Japanese version of EQ-5D-5L was translated into Japanese and validated for use in the general Japanese population.^36,37

Assessment of LupusQoL-JP reliability

The internal consistency of LupusQoL-JP was assessed using Cronbach’s α, which measures the correlation between responses to questions with the same concept.³⁸ A Cronbach’s α ≥ 0.8 indicates acceptable internal consistency reliability at the group level. Furthermore, test-retest reliability was evaluated to determine the consistency and reproducibility of responses.⁸ A subgroup of patients with stable disease activity, as determined by the SLEDAI-2K, completed the questionnaire twice, 1 week apart. For this analysis, the intraclass correlation coefficient (ICC) model 1.1 was calculated.³⁹ ICC values were interpreted as follows: >0.80 is “almost perfect,” 0.61–0.80 is “substantial,” 0.41–0.60 is “moderate,” 0.21–0.40 is “fair,” 0.01–0.20 is “slight,” and <0.01 is “poor.” These classifications were adapted from the κ coefficients interpretation criteria.⁴⁰ The test-retest reliability of the LupusQoL-JP was assessed using data only from the initial period.

Concurrent and discriminant validity of LupusQoL-JP

To evaluate concurrent and discriminant validity, Spearman’s rank correlation coefficient (ρ) was used to assess the relationship between LupusQoL-JP subscale scores and other measures, including SF-36 subscale scores and SLEDAI-2K. For concurrent validity, the correlation between LupusQoL subscale scores and comparable SF-36 subscale scores was expected range between 0.3 and 0.8, based on previous studies conducted in other countries.^{8,10,12,19,22} For discriminant validity, the correlation between the LupusQoL subscale scores and SLEDAI-2K was expected to be <0.2, as suggested by prior research conducted in other countries.^11,22 Additionally, correlations between LupusQoL-JP subscale scores and age, disease duration, prednisolone-equivalent glucocorticoid dosage, SDI, and EQ-5D-5L index values were analyzed.

Statistical analyses

Continuous variables are presented as median (interquartile range [IQR]), while categorical variables are expressed as counts and proportions (%). The SF-36 survey results were analyzed as previously described.⁴¹ Spearman’s rank correlation coefficient (ρ) was used to evaluate associations between variables, with the following interpretations: ≥0.80, very strong; 0.60–0.79, strong; 0.40–0.59, moderate; 0.20–0.39, weak. The scores of patients with and without LLDAS were compared using the Brunner-Munzel test. A two-sided p-value of <.05 was considered statistically significant. Statistical analyses were performed using Microsoft Excel software (version 2021; Microsoft, Redmond, WA, USA) and JMP Pro statistical software (version 17.0.0; SAS Institute, Cary, NC).

Results

Clinical characteristics of patients with SLE

During the initial (2011) and second (2015–2018) periods, 266 and 133 Japanese patients with SLE, respectively, completed the HRQoL questionnaires. Table 1 summarizes their demographic and disease characteristics. In brief, 92.5% (2011) and 92% (2015–2018) of participants were female, with median ages of 43.5 and 42.0 years, respectively. The median SLEDAI-2K was 2 in both periods, and the median SDI was 1 (2011) and 0 (2015–2018). Hydroxychloroquine was first approved in Japan in 2015; thus, it was not used in the initial period (2011), and only 20% of patients used it even in the second period (2015–2018).

Table 1.

Demographics and disease characteristics of the Japanese patients with SLE.

Characteristics	Number of cases (%) or median value (IQR)
	Initial period (2011)	Second period (2015–18)
	n = 266	n = 133
Age, years	43.5 (35–54)	42 (37–51)
Gender: Woman	246 (92.5)	123 (92.5)
Work status: Working [full or part time]	162/262 (61.8)	84/130 (65)
Highest attained education level
Primary	2 (1)	0
Secondary	65 (25)	29 (22)
Tertiary	190 (74)	101 (78)
Marital status: Married/other	193 (73)/73 (27)	71 (54)/60 (46)
Disease duration, years	11 (5–16)	13 (8–20)
Patients using glucocorticoid	261 (98.1)	130 (97.7)
Prednisolone dosage^a, mg/day	10 (7–10)	7.5 (5–10)
Patients using immunosuppressants^b	98 (37)	88 (66)
Patients using hydroxychloroquine	0 (0)^c	27 (20)
SLEDAI-2K score	2 (0–4)	2 (0–4)
Physician global assessment score	Not assessed	0.2 (0.0–0.5)
LLDAS attainment	Not assessed	59 (44)
SDI score	1 (0–2)	0 (0–1)
SDI score >0	166 (62.4)	53 (40)
EQ-5D-5L index value	Not assessed	0.82 (0.72–0.90)

EQ-5D-5L: 5-level EuroQoL 5-dimensions questionnaire; IQR: interquartile range; LLDAS: lupus low disease activity state; SDI: systemic lupus international collaborating clinics/American college of rheumatology damage index; SLE: systemic lupus erythematosus; SLEDAI-2K: systemic lupus erythematosus disease activity index 2000.

^aAll glucocorticoid dosages were calculated in terms of the prednisolone dosage.

^bIncludes methotrexate, azathioprine, mycophenolate mofetil, tacrolimus, ciclosporin, cyclophosphamide, mizoribine, and belimumab.

^cHydroxychloroquine was not approved and was rarely used during the initial period in Japan.

Reliability: Internal consistency

The LupusQoL-JP demonstrated high internal consistency, with Cronbach’s α of 0.90 (2011) and 0.93 (2015–2018). As shown in Table 2, the total Cronbach’s α remained >0.80 across all subscales, even when individual subscales were removed.

Table 2.

Internal consistency and test–retest reliability.

LupusQoL-JP subscale	Total Cronbach’s α with each subscale deleted		Intraclass correlation coefficient (95% CI)
LupusQoL-JP subscale	Initial period	Second period	Initial period
Total LupusQoL-JP	0.90	0.93
Physical health	0.87	0.91	0.94 (0.82, 0.98)
Emotional health	0.88	0.92	0.89 (0.65, 0.97)
Body image	0.88	0.92	0.79 (0.30, 0.95)
Pain	0.88	0.92	0.84 (0.53, 0.95)
Planning	0.87	0.91	0.95 (0.84, 0.98)
Fatigue	0.90	0.91	0.28 (−0.33, 0.73)
Intimate relationships	0.90	0.92	0.97 (0.82, 0.995)
Burden to others	0.88	0.92	0.80 (0.40, 0.94)

CI: confidence interval.

Reliability: Test-retest reliability

As shown in Table 2, LupusQoL-JP subscale scores exhibited substantial to almost perfect test-retest reliability, with ICCs ranging from 0.79 to 0.97. However, the fatigue subscale had a lower ICC (0.28) among 11 stable patients. When two patients with the largest discrepancies between test and retest scores were excluded, the fatigue ICC improved to 0.63 (95% confidence interval [CI]: 0.03, 0.90).

Score distribution

Figure 1(A) and (B) illustrate the distribution of LupusQoL-JP subscale scores for both study periods. The box plots show that most subscale scores were skewed toward higher values.

Correlation between LupusQoL-JP and SF-36 subscale scores

As shown in Table 3, the LupusQoL-JP and SF-36 scores were strongly correlated with most of the comparable domains: physical health (LupusQoL-JP) and PF (SF-36), emotional health and MH, pain and BP, and fatigue and VT. Supplemental Tables 1 and 2 summarize correlation matrices for both periods, showing that all LupusQoL-JP and SF-36 subscale scores were significantly correlated (p < .001). However, the scores for body image and intimate relationships in LupusQoL, which are unique to LupusQoL, showed only weak to moderate correlations with most SF-36 subscales.

Table 3.

Correlation (Spearman’s ρ) between LupusQoL-JP and SF-36 subscale scores with the comparable domains.

LupusQoL-JP subscale	SF-36 subscale	Spearman’s ρ (95% CI)
LupusQoL-JP subscale	SF-36 subscale	Initial period	Second period
Physical health	Physical functioning	0.65	0.76
Emotional health	Mental health	0.70	0.74
Pain	Bodily pain	0.60	0.68
Fatigue	Vitality	0.34	0.72

SF-36: medical outcomes study short form-36.

Correlation between LupusQoL-JP subscale scores and other measurements/demographics

As shown in Table 4, LupusQoL-JP subscale scores were moderately to strongly correlated with the EQ-5D-5L index values (ρ = 0.41–0.71). Furthermore, the scores of all LupusQoL-JP subscales from the initial period and some from the second period showed weak correlations with SDI. Most LupusQoL-JP subscales were not correlated with age, disease duration, prednisolone dosage, or SLEDAI-2K.

Table 4.

Correlation (Spearman’s ρ) matrix between LupusQoL-JP and other measurements/demographics.

LupusQoL-JP subscale	Age	Disease duration	Prednisolone dosage	SLEDAI-2K	SDI	EQ-5D-5 L
Initial period
Physical health	−0.13	0.04	−0.01	−0.01	−0.39
Emotional health	0.01	0.09	−0.15	−0.09	−0.27
Body image	−0.05	0.01	−0.14	−0.10	−0.39
Pain	−0.09	0.02	0.00	−0.06	−0.27
Planning	−0.11	0.01	−0.10	−0.01	−0.30
Fatigue	−0.05	0.13	−0.12	−0.15	−0.14
Intimate relationships	−0.29	−0.19	0.04	−0.02	−0.35
Burden to others	−0.02	0.05	−0.08	−0.06	−0.38
Second period
Physical health	−0.23	−0.12	−0.12	−0.08	−0.32	0.71
Emotional health	−0.03	−0.13	−0.15	−0.10	−0.09	0.60
Body image	−0.06	−0.09	−0.29	−0.23	−0.16	0.41
Pain	−0.19	−0.12	−0.08	−0.19	−0.33	0.64
Planning	−0.13	−0.11	−0.08	−0.15	−0.10	0.57
Fatigue	−0.10	−0.05	−0.27	−0.18	−0.15	0.55
Intimate relationships	−0.31	−0.09	−0.12	−0.13	−0.38	0.61
Burden to others	−0.06	−0.09	−0.09	−0.09	−0.14	0.53

EQ-5D-5L: 5-level EuroQoL 5-dimensions questionnaire; SDI: systemic lupus international collaborating clinics/American college of rheumatology damage index; SLEDAI-2K: systemic lupus erythematosus disease activity index 2000.

Spearman’s ρ with p < .05 is expressed in bold font. The EQ-5D-5L was investigated only in the second period.

Association between LupusQoL-JP subscale scores and LLDAS attainment

As shown in Figure 2, some LupusQoL-JP domains, namely, emotional health (p = .048), body image (p < .001), and fatigue (p = .0039) discriminated between LLDAS and non-LLDAS groups. However, physical health, pain, planning, intimate relationships, or burden to others did not show significant difference between LLDAS and non-LLDAS groups.

Discussion

This study confirms that the LupusQoL-JP is a valid instrument for assessing HRQoL in Japanese patients with SLE. The results from the two separate periods were consistent, thereby strengthening the reliability of our findings.

The LupusQoL-JP demonstrated excellent internal consistency with a Cronbach’s α value of >0.90, which was similar to the original study.⁸ This in turn suggests that the eight subscales of LupusQoL-JP are conceptually related.

The LupusQoL-JP subscale scores demonstrated substantial to almost perfect test-retest reliability, with ICCs values ranging from 0.79 to 0.97, except for fatigue (ICC = 0.28) among 11 stable patients. These values are also similar to the original⁸ and previous international studies.^10,12,14 The lower fatigue ICC may be attributed to differences in stable patient definitions (for example, previous studies included patients whose self-assessed HRQoL was rated stable, whereas we included patients whose SLEDAI-2K was stable) and small sample size. In fact, the ICC increased from 0.28 to 0.63 when excluding two patients with the largest difference between the two surveys. Furthermore, fatigue self-assessment may naturally fluctuate over short periods, as seen in previous studies.^8,10,12,14

Both LupusQoL-JP and SF-36 subscale scores were strongly correlated with most of the comparable domains, indicating that LupusQoL-JP has good concurrent validity, which is consistent with the original⁸ and previous international studies.^10,12,19,22 Similarly, moderate to strong correlations with EQ-5D-5L index values were observed. In contrast, body image and intimate relationships, unique to LupusQoL, showed only weak to moderate correlations with SF-36, highlighting the limitation of using generic HRQoL tools alone in capturing SLE-specific concerns.⁵

This study confirmed that LupusQoL-JP was largely independent of disease activity assessed using SLEDAI in patients with SLE, consistent with prior studies.^11,22,42 In addition, also consistent with previous studies,^9,11 some LupusQoL-JP subscales were correlated with SDI, but the correlation was weak. However, the weak association between LupusQoL and SLE disease activity/damage does not invalidate HRQoL measures,⁸ because HRQoL is often considered independent of clinical status. Finally, different disease activity measures may alter HRQoL associations, as seen in clinical trials and observational studies.⁴²

Furthermore, some of the LupusQoL-JP domains, namely, emotional health, body image, and fatigue, were able to discriminate between LLDAS and non-LLDAS groups during the second study period. In our previous study,⁷ LLDAS was not significantly associated with SF-36 summary scores of Japanese patients with SLE. By contrast, the Asia Pacific Lupus Collaboration (APLC) reported better HRQoL in LLDAS patients using SF-36¹; however, Japanese patients with SLE were not included as none of the Japanese centers had joined APLC between 2013 and 2015.¹ Differences may stem from study population variations, sample size, or statistical methods.

This study has several limitations. First, the cross-sectional nature of this study prevented tracking HRQoL changes over time. However, prior studies in other countries indicate that LupusQoL is sensitive to disease fluctuations.^42–44 Second, our study lacked data on factors influencing HRQoL, such as household income, social support, fibromyalgia, depression, comorbidity, and disability. Third, as a reflection of a cohort recruited mainly at an outpatient clinic, most participants had mild/inactive disease, thereby limiting generalizability. Finally, selection bias may exist, as participants were recruited from a university hospital, although most patients with SLE in Japan receive treatment at university or tertiary hospitals.

In conclusion, LupusQoL-JP was successfully translated, adapted, and validated for Japanese patients with SLE. It showed strong concurrent validity with comparable domains of the SF-36, but was independent of SLEDAI-2K. Patients with SLE in LLDAS had better disease-specific HRQoL in some LupusQoL-JP subscales. However, further longitudinal studies are needed to elucidate the relationships between disease activity, damage, and HRQoL in patients with SLE.

Supplemental Material

Supplemental Material - Validity and reliability of the Japanese version of LupusQoL: Assessment of disease-specific health-related quality of life in systemic lupus erythematosus

Supplemental Material for Validity and reliability of the Japanese version of LupusQoL: Assessment of disease-specific health-related quality of life in systemic lupus erythematosus by Sayuri Yamashita, Yasuhiro Katsumata, Sayumi Baba, Yuko Okamoto, Naoko Konda and Masayoshi Harigai in Journal of Lupus.

Supplemental Material

Supplemental Material - Validity and reliability of the Japanese version of LupusQoL: Assessment of disease-specific health-related quality of life in systemic lupus erythematosus

Footnotes

Acknowledgements

We would like to thank Professor Lee-Suan Teh for permitting us to translate and use the LupusQoL questionnaire in our study. We thank all the physicians who treated the enrolled patients for their engagement in data collection. We thank Enago (Crimson Interactive Pvt. Ltd) for the English language editing.

Declaration of conflicting interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: YK received honoraria from Asahi Kasei Pharma, Astellas Pharma Inc., AstraZeneca K.K., Chugai Pharmaceutical Co., Ltd., GlaxoSmithKline K.K., Janssen Pharmaceutical K.K., Mitsubishi Tanabe Pharma Corporation, Pfizer Japan Inc., Sanofi K.K. MH received honoraria from Asahi Kasei Pharma, AstraZeneca K.K., Chugai Pharmaceutical Co., Ltd., and GlaxoSmithKline K.K., grant/research support from Asahi Kasei Pharma, Astellas Pharma Inc., Chugai Pharmaceutical Co., Mitsubishi Tanabe Pharma Co. All other authors declare no competing interests.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by JSPS KAKENHI Grant Numbers JP20K08810, JP24K11395.

ORCID iD

Yasuhiro Katsumata

Supplemental Material

Supplemental material for this article is available online.

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