Abstract
Objective:
To determine the association between disease activity and choroidal thickness in patients with systemic lupus erythematosus (SLE).
Methods:
We conducted a cohort study of 24 SLE patients and 13 healthy controls recruited at Washington University School of Medicine between June 2019 and November 2021. SLE disease activity was assessed using the SLE Disease Activity Index-2000 Responder Index-50 (S2K RI-50). Patients were divided into four groups: high disease activity/no lupus nephritis (HDA/no LN; S2K RI-50 >4), HDA/active LN (HDA/active LN; S2K RI-50 >4), low disease activity/inactive LN (LDA/inactive LN; S2K RI-50 ≤ 4), and LDA/no LN (LDA/no LN; S2K RI-50 ≤ 4). LDA/no LN patients were age-, sex-, and race-matched to healthy controls and patients in other SLE groups. Choroidal thickness of the right eye was measured blinded to disease activity on a horizontal section through the fovea on optical coherence tomography images taken within a week of disease assessment.
Results:
Patients with HDA had choroidal thickening compared to matched patients with LDA. After controlling for multiplicity, choroidal thinning remained statistically significant at 1000 μm nasal to the fovea (308±68 vs 228±64μm, p=0.001). Choroidal thickness was not different between LDA/no LN and LDA/inactive LN or healthy controls.
Conclusion:
HDA in patient with SLE is associated with increased choroidal thickness whereas comorbid inactive LN did not affect choroidal thickness. Additional studies in a larger longitudinal cohort are needed to study whether choroidal thickness may be used as a noninvasive, adjunctive measure for disease activity in SLE.
Introduction
Systemic lupus erythematosus (SLE) is a chronic multisystemic autoimmune disease. Active SLE disease is associated with morbidity (1, 2) and lupus nephritis (LN) is a predictor of mortality (3). Improved biomarkers of SLE disease activity would allow clinicians to promptly and adequately treat disease flares. In LN, renal biopsy is the gold standard for diagnosis, but serial biopsies are impractical due to inherent risks of the procedure. Urine protein is routinely measured to monitor disease activity, but one third of LN patients who have complete response to standard therapies by urine protein levels continue to have active disease on biopsy (4). Thus, accurate and noninvasive methods of evaluating disease activity in SLE remain an unmet need.
Several studies show an association between SLE and changes in the eye (5, 6). The choroidal vasculature forms behind the retina in a lobular configuration with fenestrated capillary walls like the glomerulus in the kidney. Pathologic mechanisms involving immune complex deposition and inflammatory cell infiltration are thought to occur in both the choroid and the kidney, leading to thickening of the choroid (7). However, few studies have systematically examined the association between SLE disease activity and choroidal thickness (CT).
We conducted a cohort study to examine the association of disease activity with CT in age-, sex-, and race-matched patients with SLE. We hypothesized that high disease activity (HDA) would be associated with choroidal thickening in SLE.
Materials and Methods
Study population
We performed a cohort study of patients with SLE followed at the Washington University School of Medicine (WUSM) Lupus or Glomerular Diseases Clinics between June 2019 and November 2021. Patients met SLE classification using the American College of Rheumatology (8) and/or Systemic Lupus International Collaborating Clinics criteria (9). Patients with LN had biopsy-proven Renal Pathology Society/International Society of Nephrology class III, IV, and/or V LN (10). Controls were volunteers without autoimmune disease. Race/ethnicity was self-reported from a fixed set of categories. This study was approved by the WUSM Institutional Review Board (IRB ID # 201901203). Written informed consent was obtained from all participants and all procedures were performed in accordance with the Declaration of Helsinki.
Exclusion criteria included factors associated with choroidal thickness: spherical equivalent > 6 diopters or < −6 diopters, retinal disease, uveitis, pregnancy, chronic kidney disease stage 3 or greater, and severe hypertension (systolic blood pressure > 180). To control for the diurnal variation in CT, optical coherence tomography scans were only performed in the afternoon.
Assessment of SLE disease activity and laboratory values
The SLE Disease Activity-2000 Responder Index-50 (S2K RI-50) tool was used to assess SLE disease activity at each clinical visit (11). Active disease was defined as S2K RI-50 > 4 (12). Patients were evaluated by a rheumatologist or nephrologist at WUSM. Biomarkers of renal disease activity included proteinuria, hematuria, and renal function, and were assessed using spot urine protein/creatinine ratio, urinalysis, and serum creatinine obtained within a week of OCT scan, respectively. Inactive LN was defined as urine protein < 0.5 g/24 hours and return of serum creatinine to baseline. Active LN was diagnosed via renal biopsy showing active lesions within three months of OCT scan.
Patients were divided into four groups:
High disease activity, no LN (HDA/no LN, S2K RI-50 > 4), N = 4
High disease activity, active LN (HDA/active LN), N = 4
Low disease activity, inactive LN (LDA/inactive LN, S2K RI-50 ≤ 4, N = 4
Low disease activity, no LN (LDA/no LN, S2K RI-50 ≤ 4), N = 13
Healthy controls, N = 13
One patient was evaluated twice, initially with high, and subsequently with low, disease activity. These scans were included in the HDA/no LN and LDA/no LN groups.
Imaging
OCT images were collected using the extended depth imaging mode on the Heidelberg Spectralis (Heidelberg, Germany) between June 2019 and November 2021. Images were taken within one week of laboratory measurements and disease assessment. CT was measured as described previously (13). Two physicians (IL, SE) reviewed the quality of images. Measurements for statistical analysis were made by IL after blinding. Independent measurements were made by a second reviewer (AS; intraclass correlation coefficient 0.71 [95% CI 0.66-0.76]).
Statistical analysis
SPSS 28 (IBM Corporation, 1989, 2021) was used for statistical analyses. Independent Student’s t-test and linear regression were used to determine clinical factors significantly associated with continuous and normally distributed outcome variables. Kruskal-Wallis testing was used to compare lab values between groups. Wilcoxon signed-rank tests were used to determine whether LN was associated with CT using age-, sex-, and race-matched subjects. Paired t-tests were used to determine differences in CT between LDA/no LN patients and age-, sex-, and race-matched healthy controls, as well as LDA and matched HDA patients. Independent t-tests were used to compare LDA and HDA groups after subgrouping for serologic activity. Accounting for multiplicity using the Bonferroni correction, a p-value of <0.001 was considered statistically significant. Since no references for CT in HDA and LDA have been published, a priori power analysis was calculated based on a study showing choroidal thickening in SLE subjects compared to controls (14) since studies comparing LDA to controls showed thinning or no difference in CT. Disease activity was not defined for these patients. For a level of significance α=0.05, power=0.8, and correcting for multiplicity, a sample size of at least 5 pairs would be required to detect a difference between HDA and LDA subjects.
Results
Sixteen patients without LN and eight patients with LN were enrolled in the study (Table 1). Patients with LDA/no LN (n=13) were age-, sex-, and race-matched to (A) HDA/no LN (n=4), (B) HDA/active LN (n=4), (C) LDA/inactive LN (n=4), or (D) healthy control patients (n=13). Patients with HDA/active LN had the highest values for dsDNA (median 85 IU/mL, IQR 57.8-129.5; Table 1), which were different from other subgroups by Kruskal-Wallis test (H=12.8, p=0.005). C3 and C4 also had significant between-group differences by Kruskal-Wallis test (H=9.0, p=0.029 and H=8.2, p=0.042, respectively), but without significant differences on post hoc pairwise comparisons. All patients with HDA/active LN received induction therapy for LN and three of four patients (75%) had a new diagnosis of active LN. One patient had pre-existing inactive class III LN and was newly diagnosed with active class III+V LN. Patients with LDA/inactive LN included the following histologic classes: one class III, one class IV, and two class IV+V. Patients with HDA/active LN had the following histologic classes: one class III+V, one class IV+V, and one class V.
Table 1.
Demographics and characteristics of SLE patients with high and low disease activity stratified by presence or absence of LN
| High Disease Activity | Low Disease Activity | ||||
|---|---|---|---|---|---|
| Active LN (n=4) |
No LN (n = 4) |
Inactive LN (n=4) |
No LN (n=13) |
Controls (n=13) |
|
| Symbol | HDA/active LN | HDA/no LN | LDA/inactive LN | LDA/no LN | Control |
| Clinical Characteristics | |||||
| Female (%) | 4 (100) | 4 (100) | 4 (100) | 13 (100) | 13 (100) |
| Black (%) | 4 (100) | 2 (50) | 2 (50) | 6 (46) | 6 (46) |
| Age (yrs), median (IQR) | 32 (26-58) | 28 (26-38) | 31 (25-37) | 40 (29-47) | 40 (29-48) |
| Systolic blood pressure, median (IQR) | 125 (118-131) | 116 (99-131) | 114 (107-119) | 127 (110-142) | 124 (113-132) |
| Lupus duration (yrs), median (IQR) | 5 (4-12) | 2 (0.6-10) | 13 (6-14) | 11 (8-16) | - |
| Steroids (%) | 2 (50) | 1 (25) | 0 (0) | 1 (7.7) | - |
| HCQ (%) | 4 (100) | 4 (100) | 3 (75) | 9 (69) | - |
| Other immunosuppressant medications (%) | 4 (100)1 | 3 (75)2 | 3 (75)3 | 5 (38)4 | - |
| S2K RI-50, median (IQR) | 15 (7-16) | 7 (6-8) | 2 (0.5-2) | 2 (0-2) | - |
| dsDNA (IU/mL) | 85 (57.8-129.5) | 1.5 (1-14.8) | 38 (18.8-63.3) | 3 (1-7.5) | |
| C3 (mg/dL) | 84 (69-99) | 90 (77-128) | 97 (90-118) | 137 (107-164) | |
| C4 (mg/dL) | 13.4 (8.8-17.8) | 10.7 (7.2-22.5) | 14.6 (13.7-22.7) | 26.8 (16.9-31.3) | |
| ESR (mm/hr) | 40 (23-59) | 17 (8-47) | 9 (6-9)6 | 31 (17-73)6 | |
| CRP (mg/L) | 1.8 (0.6-5.9) | 1.4 (0.3-2.5) | 1.1 (0-1.1)6 | 4.1 (1.4-10.1) | |
| Scan Characteristics | |||||
| Axial length (mm), median (IQR) | 23.9 (23.3-24.9) | 23.3 (22.9-24.6) | 23.4 (22.4-25.3) | 24.0 (23.5-24.9)5 | 24.1 (23.0-24.3) |
yrs, years; IQR, interquartile range.
4 patients on cellcept, 1 patient on rituximab
1 patient on azathioprine, 1 patient on rituximab, 2 patients on belimumab
3 patients on cellcept, 1 patient on belimumab
1 patient on azathioprine, 1 patient on rituximab, 3 patients on belimumab
p = 0.584 for control vs non-LN SLE with low disease activity
1 missing value
Choroidal thickness
On univariate analysis, age was associated with CT in patients with SLE in all subgroups at 1500 μm (β=−3.7±1.6, p=0.028), 1000 μm (β=−3.5±1.4, p=0.023), and 500 μm (β=−2.8±1.3, p=0.041) temporal to the fovea. Steroid use and years of SLE diagnosis were not associated with CT. Axial length and smoking status were not associated with CT for the combined group of healthy controls and patients with SLE (data not shown).
Wilcoxon signed-rank test was used to compare LDA/no LN to LDA/inactive LN matched by age, sex, and race. LDA/no LN did not have different CT compared to patients with LDA/inactive LN (Figure 1A), therefore we combined the two LDA groups to examine the association of disease activity with CT. Paired t-tests between HDA patients (n=8) and matched LDA patients (n=8) showed globally thicker choroids in HDA patients, which was statistically significant 1000 μm (308±24 vs 228±23μm, p=0.001) nasal to the fovea (Figure 1B) with a Cohen’s d of 1.2. In the subset of patients with LDA and HDA who were serologically active (n=7) or inactive (n=4) based on dsDNA, C3, or C4 values, serologically active HDA patients had thicker choroids 1500 μm (293±37 vs 167±37μm, p=0.042) and 1000 μm (307±36 vs 175±38μm, p=0.039) temporal to the fovea, at the fovea (302±31 vs 197±29μm, p=0.038), and 1000 μm (308±28 vs 197±34μm, p=0.038) and 1500 μm (296±28 vs 185±32μm, p=0.034) nasal to the fovea (Figure 2). Paired t-tests between patients with LDA/no LN matched to healthy controls showed choroidal thinning that was not statistically significant after Bonferroni correction (Figure 1C, Table S1).
Figure 1.
Violin plots of choroidal thicknesses of age-, race-, and sex-matched (A) LDA/no LN vs LDA/inactive LN, (B) LDA vs HDA, and (C) LDA/no LN vs healthy controls at seven locations measured in a horizontal section through the fovea. *p<0.05, **p<0.005
Figure 2.
Violin plot of choroidal thicknesses of serologically inactive patients with LDA vs serologically active patients with HDA at seven locations measured in a horizontal section through the fovea. *p<0.05
Discussion
Our study showed an association between high disease activity and choroidal thickening in patients with SLE, which was statistically significant 1000 μm nasal to the fovea after controlling for multiplicity. We also showed that LDA/no LN compared to LDA/inactive LN or healthy controls was not associated with change in CT after controlling for multiplicity. Although small sample size prevents wide generalization of this study, these findings support future longitudinal studies testing the hypothesis that disease activity in SLE patients is associated with choroidal thickening.
While variable association between SLE and CT is described in the literature, only recent studies systematically evaluated patients with validated disease activity scores (6), and most studies have not examined the association of disease activity with CT. We observed an association between HDA and thicker choroid after matching for race, sex, and age with a large effect size (Cohen’s d of 1.2). Furthermore, the inclusion of only patients with HDA and active serologic markers increased mean difference in CT compared to LDA with inactive serologic markers. Since the vascular design of the choroid of the eye and glomerulus of the kidney are similar, choroidal thickening may represent immune complex deposition and inflammation in the choroid, similar to that seen in the glomerulus in proliferative LN. Choroidal thickening seen in association with HDA may also represent a spectrum of disease with lupus choroidopathy, a vision-threatening ophthalmic condition in SLE that is associated with HDA in SLE, including lupus nephritis and CNS vasculitis (7). If these findings are reproduced in future longitudinal studies, this would suggest that CT can be used as an adjunctive measurement of disease activity in SLE in addition to currently used renal biopsies and urine protein levels.
Our methods comparing patients with LDA to healthy controls were similar to those of Dias-Santos et al., who did not find thinning of the choroid in LDA SLE patients (6) after correcting for multiple confounders including the presence of LN. Our study adds to the literature due to inclusion of a high percentage of female and Black patients.
In examining the association of LN with CT, previous groups have found varied CT in patients with LN compared to non-LN SLE (5). Dias-Santos et al., found that choroidal thinning was associated with diagnosis of LN after controlling for multiple confounders (6). However, the degree of clinical remission (degree of proteinuria and chronic kidney disease staging) was not described. Since chronic kidney disease and proteinuria were previously associated with choroidal thinning (15), we only included patients in the inactive lupus group with urine protein < 0.5 g/day and estimated glomerular filtration rate of > 60 mL/min/1.73 m2. In a retrospective study, we found no difference in CT between patients with inactive LN and non-LN SLE without extrarenal flare, but were unable to capture S2K RI-50 (13). In this current study, we similarly found no difference in CT between LDA/no LN and LN regardless of disease activity based on S2K RI-50.
Limitations of this study include the cross-sectional study design, small sample size, and lack of male patients with SLE in this study. The small sample size and lack of male patients both limit the generalizability of this study. Larger, more sex diverse, and longitudinal studies will be needed to verify the association of disease activity on CT. Strengths of this study include expert systematic evaluation by specialists and matching patients based on by age, race, and sex. Our cohort included a high percentage of Black patients, who are not well represented in prior literature. Finally, patients diagnosed with LN had a biopsy-proven diagnosis, and those with active LN disease had recent biopsy-proven disease activity, which is important due to high rates of discordance between clinical and histological disease activity.
In summary, we present a cohort study that found an association between disease activity and increased CT in patients with SLE. Future studies will involve larger cohorts of patients followed longitudinally to better characterize the association of disease activity with the choroid and the retinal vasculature.
Supplementary Material
Acknowledgements:
We acknowledge Casey Hatscher, Anna Antiporda, Sandra Quirin, Eve Adcock, and Silvana Bommarito for acquiring ophthalmic images and coordinating patient visits.
Funding:
Funding support was provided by the National Institute of Health (NIH)/National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) 2T32AR007279-41A1 and the Washington University in St. Louis Division of Nephrology Clinical Innovation Grant. Research reported in this publication was also supported by the Washington University Institute of Clinical and Translational Sciences grant UL1TR002345 from the National Center for Advancing Translational Sciences (NCATS) of the National Institutes of Health (NIH). The content is solely the responsibility of the authors and does not necessarily represent the official view of the NIH. RSA is supported by NIH grant EY019287, the Jeffrey Fort Innovation Fund, the Starr Foundation, and an unrestricted grant from Research to Prevent Blindness, New York, NY to the Department of Ophthalmology, Washington University School of Medicine, St. Louis, MO.
Footnotes
Conflicts of interest: AHJK has sponsored research agreements from Foghorn Therapeutics and GlaxoSmithKline unrelated to this work. AHJK also receives personal fees from Alexion Pharmaceuticals, AstraZeneca, Aurinia Pharmaceuticals, Exagen Diagnostics, GlaxoSmithKline, and Pfizer. TL receives research support from Travere Therapeutics, Genentech, Omeros Corporation, and NIH/NIAID, and reports consultancy agreements with ChemoCentryx, Travere Therapeutics, Aurinia Pharmaceuticals, Calliditas Therapeutics, and GlaxoSmithKline.
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