We analyzed real-word data from a large cohort of patients with SLE, collected from both the patients and their managing physicians, in the USA and Europe. Our findings demonstrated that patients achieving a low disease activity at a given point in time had lower previous flaring rates, fatigue, productivity impairment (in particular, lower levels of absenteeism), income loss and HCRU, and better health status, compared with patients who had higher active disease or had not achieved low disease activity during the same time.
Our finding of a strong association of low disease activity with reduced flaring has been previously reported in a prospective cohort study across 13 centers in eight Asia Pacific countries, in which low disease activity was defined via the LLDAS [15].
We showed low disease activity to be associated with better health status, as assessed with the EQ-5D-3L. The mean EQ-5D-3L utility index of 0.79 that we observed among those with higher active disease was below population norms reported for females from Europe (0.89) and the USA (0.85), indicating that our analysis cohort (which consisted of almost 90% females) had poorer health status than the general population. The mean EQ5D3L health utility index of 0.88 for patients with low disease activity suggests health status on a par with the general population [24]. Our finding that patients with low disease reported an average EQ-5D-3L score 0.09 points higher than patients with higher disease suggests there is likely to be a observable difference in HRQoL in these patients as this difference is higher than 0.07, the minimal clinically important difference (MCID) for this measure in SLE [41]. While few studies have examined EQ-5D-3L scores in relation to disease activity in SLE, there are two studies that found an association of overall health status with disease activity. In the first study they reported modest correlations between SLEDAI score and EQ-5D-3L VAS in Canada [42], and similar findings were reported in a second study in China between SLEDAI2K score and EQ-5D-3L utility index [43]. A Swedish study also reported a significant association of EQ-5D-3L utility index and disease activity, although in that study disease activity was measured using the patient-reported SLAQ and glucocorticoid dose [44].
Other PROs have been utilized in studies investigating the relationship of disease activity in SLE with HRQoL. A cross-sectional Brazilian study showed higher disease activity as assessed via the SLEDAI2K in women with SLE to be associated with poorer HRQoL assessed with the World Health Organization Quality of Life Group (WHOQOL-100) assessment instrument [45]. A Swiss cohort study reported similar findings, with increases in disease activity assessed by the SELENA-SLEDAI negatively correlated with the physical and mental component summaries of the SF-36, signifying reduced HRQoL [46].
We observed a mean FACIT-Fatigue sum score of 39.79 in patients with low disease activity and a mean sum score of 34.78 among those with higher active disease, these were both lower than the mean of 43.6 reported for > 1,000 and > 2,400 members of the general population in the US and Germany [25, 47]. This indicates that fatigue in both groups of SLE patients is worse than in the general population. Findings in the literature on the association between SLE disease activity and fatigue severity are mixed, with two published US studies reporting no significant association of disease activity with fatigue assessed [48, 49] while two studies observed similar findings as we reported here, with fatigue being worse in patients with more severe disease [50, 51]. One study exploring MCIDs in SLE reported that FACIT-F scores among patients experiencing “much more fatigue” differed from those feeling “somewhat more fatigued” by 15.0 points which is smaller than the difference we found between patients with low and higher disease activity [52] suggesting that this difference in score may not have an impact on patient HRQoL.
We saw a much lower impact on productivity, and consequently on income, in patients with low disease activity. Absenteeism was only 0.17%, with a consequent income loss of $63/year, in patients with low disease activity, but in patients with higher active disease these were close to 8% and more than $2,300/year. When presenteeism was also considered, the difference between patients with low disease activity and higher active disease was even more marked: overall work impairment and annual income loss were 14% and $5,400 in patients with low disease activity but more than doubled to 37% and $11,400 in patients with higher active disease.
In an analysis of data from a large population-based US SLE cohort, overall work impairment assessed with the WPAI was correlated with disease activity assessed with the SLAQ [53]. Higher self-reported disease severity was also directly associated with higher levels of absenteeism and presenteeism in a survey of patients with SLE in the USA [54]. An analysis of a large cohort of US SLE patients reported that disease activity, assessed via the SLAQ, was a significant predictor of reduced work productivity [55]. Published studies have also shown the indirect costs of SLE, including lost earnings, to be related to disease activity [55, 56]. Collectively, these data underscore the importance of disease activity in the burden of illness in SLE from the patient perspective.
In our study, patients with low disease activity had 28% fewer HCP consultations in the 12 months prior to data collection, compared with patients with higher active disease. In the 12 previous months, only 4% of patients with low disease activity were hospitalized, compared with 15% of those with higher active disease. The lower HCRU that we observed in patients with low disease activity is consistent with previous published studies. Reductions in disease activity assessed with the SLEDAI2K were associated with reductions in HCRU and healthcare costs in a retrospective longitudinal study of SLE patients in the USA [57]. Analysis of a cohort of SLE patients from various regions of Sweden reported indirect and direct healthcare costs (which relate to HCRU) around 50% higher in patients with a SLEDAI-2K score ≥ 4 compared with patients with SLEDAI-2K score < 4 [58]. In an SLE patient cohort from a single tertiary hospital in Australia, patients in LLDAS for ≥ 50% of the observation period incurred significantly lower (by 26%) annual direct healthcare costs than those in LLDAS for < 50% of the time [12]. A retrospective, observational cohort study of patients with SLE from the Japan Medical Data Center claims database identified increasing HCRU and cost with increasing disease severity, with disease severity defined based on an algorithm that included SLEDAI score with a number of other parameters [59].
We observed discrepancies between subjective physician-reported disease severity and objectively defined disease activity, with 58% of patients classified as having higher active disease being considered by their physicians to have mild SLE. Excluding patients defined as having higher active disease on the basis of receiving glucocorticoid at a dose of > 7.5mg/day reduced the patients classified as having higher active disease but considered by their physicians to have mild SLE to 48%, but this is still a marked misalignment of these means of assessing SLE. The lack of clear alignment of subjective physician-reported disease severity with the disease activity groups defined for the purposes of this analysis highlighted the challenges of assessing disease activity in SLE. The differences demonstrated in flaring, PROs and HCRU between patients with low disease activity and active disease even when including patients that physicians considered to have mild SLE in the active disease group indicated that the criteria used in defining disease activity, including SLEDAI-2K score and receipt of high-dose glucocorticoid, are associated with the humanistic and economic burden of SLE.
There were potential limitations to our study. Despite the large number of study participants, missing data (particularly PRO data) resulted in small sample sizes being available for some analyses. Data were included for the next five consecutively consulting patients; the study sample was therefore pseudo-random, rather than truly random, and the study population could include a high proportion of patients who consult their physician more frequently than is typical in SLE, and who may be atypical in other ways. The point-in-time nature of the survey allowed assessment of the association between factors but precluded assessment of causality. Our methodology relied on accurate recall and reporting by physicians and patients, and missing data were expected but may have influenced results—always a challenge in this type of study. While the mean age and preponderance of females in our dataset reflected published demographics for SLE, our study population included a high proportion of White patients, although globally SLE has a higher prevalence in other ethnic groups. As non-White SLE patients have a higher likelihood of developing severe disease with poor outcomes [60, 61] caution should be exercised in extrapolation of these findings to a broader population.
Our data source did not include some of the data used to define low disease activity in the published definition of LLDAS (Franklyn et al 2016, Golder et al 2019), and we were therefore not able to classify patients based exactly on that definition. However, patients that we defined as having higher active disease had a SLEDAI-2K score ≤ 4 and/or were receiving ≤ 7.5 mg/day glucocorticoid, and therefore would be excluded from the LLDAS group based on the published definition. A total of 23 patients that we classified as having low disease activity were receiving an immunosuppressant or biologic, but insufficient data were available to ascertain whether all of these therapies were at well-tolerated standard maintenance doses, as required in the published definition of LLDAS.
Despite the limitations, real-world studies play an important role in exploring areas of concern that cannot be addressed in randomized clinical trials. Patients included in clinical trials represent only a small proportion of the consulting population as a result of the stringent eligibility criteria that patients are required to meet to be involved, for example, patients tend to be younger and without comorbidities [62]. Similarly, patients treated in the real-world setting may be less likely to be adherent to medication than those included in clinical trials.and therefore better reflect outcomes of patients in the real-world [63] As a result, data from real-world studies can complement clinical trials and provide insight into the effective of interventions in patients commonly seen in clinical practice.
Our analysis of a large real-world patient cohort from multiple countries and two continents provided insight into the association of clinical, humanistic and economic outcomes with disease activity in SLE. Our findings indicated that patients with low disease activity experienced significantly better health status, less fatigue, and lower levels of productivity impairment, and were less burdensome to the healthcare system than those with higher active disease. We are hopeful that with an established definition of low SLE disease activity in place, there will be a useful guide for treatment goals and an aid to assess drugs in development and their potential to improve patient outcomes and reduce HCRU.