This study investigated whether the eDII is associated with the inflammatory burden or the depressive status in patients with AAV and obtained several interesting findings. First, the eDII scores inversely correlated with only SF-36 MCS with a statistically significant difference. Second, when the patients with AAV were divided into two groups according to the eDII scores, those in the higher eDII group exhibited significantly lower median SF-36 MCS than those in the lower eDII group. Third, patients in the higher eDII group exhibited a significantly higher risk for the lowest tertile of SF-36 MCS than those in the lower eDII group (RR 3.000). Therefore, we can conclude that the eDII scores can predict the current depressive status based on SF-36 MCS scores.
The depressive status should be defined based on K-CESD-R ≥ 16 . However, at the start of this study, a correlation between the eDII scores and BVAS or the values of acute-phase reactants was expected; thus, we did not fill out the K-CESD-R form in this study. Nevertheless, we replaced the lowest tertile of SF-36 MCS with the cut-off of SF-36 MCS based on K-CESD-R ≥ 16 to determine the depressive status. This was done because the cut-off of SF-36 MCS, which can predict the depressive status based on K-CESD-R ≥ 16, was close to the upper limit of the lowest tertile value of 50.0 in a previous study . In this study, the upper limit of the lowest SF-36 MCS was 55.31. If K-CESD-R had been used to assess the study participants, the cut-off of SF-36 MCS for the depressive status based on K-CESD-R would be close to 55.31, because the patients were selected from the same cohort as of the previous study. It is believed that the eDII scores are clinically significant in patients with AAV in the higher eDII group, who may be more susceptible to the depressive status based on the lowest tertile of SF-36 MCS than those in the lower eDII group.
There is a temporal difference between the eDII and SF-36 MCS questionnaires. SF-36 MCS assesses the mental health and emotional state over the past month, while the eDII scores assess the food intake over the past week [16, 17]. Given the time gap, this study investigated whether the eDII score directly predicted the lowest tertile of SF-36 and indirectly predicted the depressive status. As food intake patterns are more of habit than taste, they tend to persist over a relatively long period of time rather than change over a short period. Therefore, we can conclude that the results of this study are reliable. Moreover, the eDII score is more suitable for predicting SF-36 MCS with relatively small changes in the long term than BVAS or CRP levels with large changes in the short term.
Additionally, although the eDII score did not significantly correlate with the AAV-specific indices other than SF-36 MCS and acute-phase reactants, we compared their median values between the higher and lower eDII groups (Fig. 1B. Among the measures of SF-36 PCS, BVAS, VDI, ESR, and CRP, patients in the higher eDII score group exhibited a higher median BVAS than those in the lower group (5.0 vs. 4.0, P = 0.099) (Supplementary Fig. 1). However, this difference was not statistically significant. We conclude that the eDII score may not be useful in estimating the cross-sectional inflammatory burden based on BVAS or acute-phase reactants.
The strength of this study is that for the first time, the inverse correlation between the conveniently revised eDII scores based on the DII and the cross-sectional SF-36 MCS score was revealed. However, this study also has several limitations that should be considered. The number of patients with AAV participating in this study was not adequate to generalise the results to all Korean patients with AAV. Furthermore, this study was designed to compare both the eDII scores and the AAV-specific indices at two different time points. However, the follow-up eDII score could not be completed, because a significant number of patients did not respond to the eDII and SF-36 questionnaires due to the SARS-CoV-2 pandemic. Since this study was conducted during the pandemic, it is unclear whether the study accurately reflected the situation before or after the pandemic. Therefore, if future studies with a large number of patients with AAV that involve completing the DII and SF-36 MCS questionnaires at two or more different times after the pandemic are warranted, they could provide dynamic and more reliable information regarding the clinical implications of the eDII for managing patients with AAV in actual clinical practice.