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Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

Objective

The Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index (SDI) is a validated instrument for assessing organ damage in systemic lupus erythematosus (SLE). Trained physicians must complete it, thus limiting utility where this is impossible.

Methods

We developed and pilot tested a self-assessed organ damage instrument, the Lupus Damage Index Questionnaire (LDIQ), in 37 SLE subjects and 7 physicians. After refinement, 569 English-speaking SLE subjects and 14 rheumatologists from 11 international SLE clinics participated in validation. Subjects and physicians completed the instruments separately. We calculated sensitivity, specificity, Spearman's correlations, and agreement using the SDI as the gold standard. Six hundred five SLE participants in the community-based National Data Bank for Rheumatic Diseases (NDB) study completed the LDIQ and we assessed correlations with outcome and disability measures.

Results

The mean LDIQ score was 3.3 (range 0–16) and the mean SDI score was 1.5 (range 0–9). The LDIQ had a moderately high correlation with the SDI (Spearman's r = 0.50, P < 0.001). Specificities of individual LDIQ items were >80%, except for neuropathy. Sensitivities were variable and lowest for damage, with <1% prevalence. Agreement between the SDI and LDIQ was >85% for all but neuropathy, reduced renal function, deforming arthritis, and alopecia. In the NDB, the LDIQ correlated well with the comorbidity index (r = 0.45), the Short Form 36 physical component scale (r = 0.43), the Medical Research Council dyspnea scale (r = 0.40), disability (r = 0.37), and the Systemic Lupus Erythematosus Activity Questionnaire score (r = 0.37).

Conclusion

The metric properties of the LDIQ are good compared with the SDI. It has construct validity and correlations with health assessments similar to the SDI. The LDIQ should allow expansion of SLE research. Its ultimate value will be determined in longitudinal studies.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

The overall prognosis in systemic lupus erythematosus (SLE) has improved since the 1950s, with 10-year survival rates now 85% or better (1). Unfortunately, however, patients with SLE still have significant clinical manifestations and often irreversible organ damage, including accelerated atherosclerotic vascular disease (2), osteoporosis (3), and other sequelae of disease activity and immunosuppressive therapies (4).

The Systemic Lupus International Collaborating Clinics (SLICC)/American College of Rheumatology (ACR) Damage Index (SDI) is a 42-item questionnaire concerning long-term damage due to SLE in 12 organ systems for use in clinical research studies (5–8). The SDI was developed between 1985 and 1996 by a panel of SLE experts and members of SLICC, a multinational collaboration of SLE centers (9). The SDI is completed by the physician at enrollment in clinical studies and assesses major irreversible organ damage and treatment toxicity, including stroke, loss of extremity, malignancy, and premature gonadal failure. Damage from SLE is defined as “an irreversible change in an organ or system that has occurred since the onset of SLE, and present for at least 6 months” (5). Each item is assessed as present or absent, and scores of 2 or 3 are possible for recurrent events (e.g., stroke) or serious damage (e.g., end-stage renal disease). Only complications that occur after the onset of SLE are assessed. The widely used index was reviewed at each of the SLICC participating medical centers for content and face validity (6). Interobserver variability of the index when performed by different members of SLICC was good (10). Retrospective completion of the SDI by another physician reviewing medical records has also been shown to be valid (11), and the SDI has been endorsed by the ACR and validated in multiple international settings (6, 12–14). The SDI is predictive of both long-term survival and quality of life for patients with SLE (15–17).

Often in clinical research in SLE, however, it is not practical to request that many busy physicians complete time-consuming forms and assessments, in particular in large national cohort studies. We aimed to develop and validate a patient self-administered version of the SDI, the Lupus Damage Index Questionnaire (LDIQ), for use where direct assessment by physicians is not practical. A self-reported instrument would enable assessment of organ damage in community-based SLE patients without requiring participation of trained physicians familiar with the SDI. This would facilitate assessment of SLE-related organ damage in epidemiologic cohort studies in which subjects are followed in the community, ultimately allowing the expansion of SLE investigations beyond academic centers.

PATIENTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

This study proceeded in 3 stages: 1) initial development, pilot testing, and revisions, 2) a multicenter clinic-based validation study, and 3) a mail-based validation study in a separate longitudinal cohort of community-based US participants with SLE, the National Data Bank for Rheumatic Diseases (NDB), to assess construct validity and correlates of the LDIQ.

Subject selection

Eligible subjects for all of the stages had SLE according to the updated ACR criteria (18, 19) and were age >18 years. Development and stage 1 piloting took place at the Brigham and Women's Hospital in Boston, Massachusetts, and the University of Alabama at Birmingham in Birmingham, Alabama. Stage 2 was a multicenter validation performed at 11 different clinical lupus centers in the US, Canada, and the UK. Eligible physicians for both stages consisted of trained attending rheumatologists specializing in SLE at these clinical centers and with experience in completing the SDI instrument. In stage 3, community-based SLE participants in the NDB, a longitudinal study of rheumatic disease outcomes, completed the LDIQ. These participants were followed longitudinally with semiannual, detailed, 28-page questionnaires, as previously described (20, 21). SLE participants were initially enrolled largely by rheumatologist referral, but also by self-referral after confirmation of SLE by their rheumatologist.

Data collection.

Stage 1: development, pilot testing, and refinement.

All SDI items (42 items in 12 organ systems) were translated into lay language questions (55 total questions), to which subjects were asked to respond “yes” or “no.” Several clinical researchers, clinicians, and literacy experts reviewed the translation, attempting to target an eighth-grade reading level. The questions were reviewed and refined by the developers (KHC, GSA, FW), and the performance of this instrument was then assessed in a pilot study involving 37 SLE subjects (22). These subjects were asked to complete the 3-page pilot LDIQ and their rheumatologists separately completed and returned the SDI, blinded to subject responses. Subjects were also asked to circle words and questions that they did not understand and to make comments in provided space. Subjects who did not read English, who refused to complete the questionnaire, or whose physicians did not want their patients to participate were not included. Although overall metric properties of the LDIQ were good, a few items on the questionnaire were thought to produce false-positive or false-negative responses from the subjects. We refined these items, changing the wording of problematic questions. Rather than including a “don't know” response for each item, which may have had a high response rate, the directions stated, “Don't worry if there are some medical words you don't understand. This usually means that you don't have the problem the question is asking about.”

Stage 2: multicenter validation of the self-assessed LDIQ

We tested the revised index, comparing it with the physician-reported SDI as above in a multicenter study. We contacted 11 SLE centers in the US, Canada, and the UK, and invited them to participate in this validation study. Consecutive English-speaking SLE patients were recruited to fill out the questionnaire in each clinical setting during the months of July 2007 to December 2007. Independently, the rheumatologists seeing the subjects that day completed an SDI for each subject. In a subset of 51 of these subjects at the Brigham and Women's Hospital and the University of Alabama at Birmingham, the questionnaire was mailed to the participant rather than completed during an office visit, and the rheumatologist independently completed and returned the SDI.

Stage 3: NDB-based validation of the LDIQ

From September 2007 to December 2007, we asked 673 SLE participants in the NDB to complete the LDIQ at the time of their semiannual questionnaires for the ongoing cohort study. Participants also completed the Short Form 36 (SF-36), from which the physical component summary (PCS) and mental component summary (MCS) scores are derived (23, 24); the Medical Research Council dyspnea index (25); the Health Assessment Questionnaire (HAQ) (26); visual analog scales for pain, global, and fatigue; and measures of service utilization, treatments, and medical costs. We examined data for the Systemic Lupus Erythematosus Activity Questionnaire (SLAQ), completed 6 months previously. The SLAQ, a patient-reported version of the physician-reported Systemic Lupus Activity Measure, is a validated 24-item questionnaire that reduces to 17 items for scoring and has a range of 0–44 (27–29). Comorbidity was measured by a patient-reported composite comorbidity index (range 0–9) comprised of 11 present or past comorbid conditions, including pulmonary disorders, myocardial infarction, other cardiovascular disorders, stroke, hypertension, diabetes mellitus, spine/hip/leg fracture, depression, gastrointestinal (GI) ulcer, other GI disorders, and cancer (30, 31).

All of the forms were returned to the central processing site, the NDB in Wichita, Kansas. Questionnaires completed by the subjects and physicians in all stages of the study were anonymized and tracked only study numbers. Institutional review board approval from all of the participating institutions was obtained for all aspects of this study.

Statistical analysis.

Stages 1 and 2.

Data collected from the SDI and LDIQ were dichotomous responses to a series of questions to assess the severity of damage associated with the subject's SLE. For each question on the LDIQ, the subject's response was recorded as either true-positive, true-negative, false-positive, or false-negative, using the responses provided by the physicians on the SDI for that patient as the gold standard. The performance of the LDIQ in assessing SLE damage was analyzed by calculating the mean sensitivity, specificity, percent agreement, and kappa agreement statistic for the subjects and physicians for each item on the LDIQ and for the overall questionnaire, using the SDI as the gold standard. We calculated Spearman's correlation coefficients comparing organ damage domains and total scores on the LDIQ and SDI. We examined agreement in SLE subject and physician scores as a function of SLE disease duration employing linear regression analyses.

Stage 3

Associations between the LDIQ, comorbidity index, patient global, and other study variables were investigated by Spearman's correlation coefficients. Associations between reported work disability and the SF-36 PCS and LDIQ and their domains were investigated using Kendall's tau-a. Kendall's tau-a is related to the area under the receiver operating characteristic curve, and allows us to understand the degree to which variables are simultaneously associated with the LDIQ domains. Kendall's tau-a has a simple interpretation: the percent concordance between variables. For example, a value of 0.151 indicates that it is 15.1% more likely that a person with disabilities will have a high neuropsychiatric domain score than a person without disabilities will have such a score. For the SF-36 PCS, the comparison is a score above and below the median.

Data were analyzed using Stata, version 10.1 (StataCorp, College Station, TX), for all statistical analyses. Statistical significance was set at the 0.05 level and all tests were 2-tailed.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

The demographic characteristics of the subject populations in stages 1, 2, and 3 are shown in Table 1. In general, the study subjects were predominantly women, with 10–16 years of SLE. The subjects in the stage 1 initial pilot were slightly younger and had a shorter mean disease duration compared with those in the stage 2 validation.

Table 1. Demographic characteristics of the subjects*
 Stage 1: pilot testingStage 2: multicenter clinic-based validationStage 3: NDB mailed survey
  • *

    Values are the mean ± SD unless otherwise indicated. NDB = National Data Bank for Rheumatic Diseases.

Total no. of subjects37569605
Women, %899394.9
Age, years38.9 ± 13.344.0 ± 13.451.7 ± 13.6
Race/ethnicity, %   
 White656989
 Asian861
 African American22176
 Hispanic552
 Other032
Disease duration,  years9.7 ± 8.714.0 ± 10.817.8 ± 11.8
Education, years15.0 ± 2.714.4 ± 2.413.7 ± 2.4

Stage 1: development, pilot testing, and revisions

Thirty- seven English-speaking SLE subjects and 7 rheumatologists at 2 US SLE centers participated in LDIQ initial development and pilot testing. The overall sensitivity of the pilot LDIQ was 92.4%, specificity was 94.9%, and agreement was 94.4%. Several items needed further refinement because there were either false-positives (end-stage renal disease, cognitive impairment, alopecia, scarring skin, and claudication) or false-negatives (retinal changes, muscle atrophy, and osteomyelitis) when compared with the SDI responses. The refined LDIQ included 56 questions organized into 12 organ damage domains (see Supplementary Appendix A, available in the online version of this article at http://www3.interscience.wiley.com/journal/77005015/home).

Stage 2: multicenter office-based validation

Five hundred sixty-nine English-speaking subjects with SLE and 14 trained SLE rheumatologists from 11 academic medical centers in the US, UK, and Canada participated in the multicenter validation. Subject demographics are shown in Table 1. Of the physicians, 56% were women, with a mean ± SD age of 49 ± 9.6 years and a mean ± SD of 16.8 ± 8.4 years in practice, and 100% had formal rheumatology and SLE training. The questionnaire took most subjects less than 10 minutes to complete. The overall metric properties of the LDIQ compared with the SDI of this study are shown in Table 2. The mean score across the LDIQ items was 3.30 (range 0–16) and the mean physician SDI score was 1.53 (range 0–9). The mean sensitivity, specificity, and agreement were 53.3%, 94.6%, and 93.2%, respectively, reflecting good overall agreement between the LDIQ and the SDI. The LDIQ had a moderately high correlation with the SDI (Spearman's r = 0.48, P < 0.001). When stratified by the subjects' educational level, the correlations between the LDIQ and the SDI were surprisingly lower among subjects with higher educational levels: Spearman's r = 0.49 for subjects above the mean educational level and Spearman's r = 0.54 among subjects at or below the mean. A comparison of responses with the LDIQ by SLE subjects and the SDI by their rheumatologists by individual organ system item is shown in Table 3. Specificities of individual LDIQ items were all >80% except for neuropathy (78.7%). Sensitivities were variable, and low for low prevalence damage, such as myocardial infarction, significant tissue loss, GI infarction, GI stricture, or surgery. Agreement between physician and patient was >85% for all items except neuropathy, reduced renal function, deforming arthritis, and alopecia. Kappa agreement statistics were also variable, but above 0.30 for most of the items. Using linear regression, we found an increase of 0.03 points (95% confidence interval 0.01–0.05) in disagreement between subject LDIQ and physician SDI per year of SLE duration. Among the 51 subjects who received and returned the LDIQ by mail, overall agreement with their physicians' SDI scores was high (ranging from 80% to 100%). The mean subject LDIQ score was 3.3 (range 0–11), the mean physician SDI score was 1.6 (range 0–7), and the Spearman's correlation between the two was again high (r = 0.71, P < 0.001).

Table 2. Overall performance of the LDIQ*
 Stage 1: pilot testing and refinementStage 2: multicenter clinic-based validationStage 3: NDB mailed survey
Mean ± SDRangeMean ± SDRangeMean ± SDRange
  • *

    LDIQ = Lupus Damage Index Questionnaire; NDB = National Data Bank for Rheumatic Diseases.

Sensitivity, %80.7 ± 35.00–10053.3 ± 29.10–100.066.1 ± 44.80–100.0
Specificity, %94.8 ± 7.866.7–10094.6 ± 5.678.7–99.693.5 ± 6.481.2–98.0
Overall agreement, %94.5 ± 7.464.7–10093.2 ± 5.577.7–98.881.7 ± 16.550.0–98.0
Table 3. Comparison of organ system responses by 569 SLE subjects on the LDIQ with rheumatologists' responses on the SDI in the multicenter validation*
Damage itemPrevalence, %Sensitivity, %Specificity, %Agreement, %Kappa test for agreement
  • *

    SLE = systemic lupus erythematosus; LDIQ = Lupus Damage Index Questionnaire; SDI = Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index.

Cataract9.388.792.894.40.65
Retinal damage4.262.596.094.50.46
Seizure5.155.296.594.40.47
Stroke0.566.799.595.10.51
Neuropathy5.158.678.777.70.14
Transverse myelitis1.257.187.987.50.08
Decreased renal function5.2493.580.180.80.28
Pulmonary hypertension2.361.596.996.10.40
Pulmonary fibrosis3.266.796.095.10.44
Shrinking lung0.5100.094.094.00.14
Pleural fibrosis1.257.196.896.30.26
Pulmonary infarction1.4100.093.893.90.30
Angina/surgery4.975.096.595.40.60
Myocardial infarction0.40.099.697.00.47
Cardiomyopathy1.644.497.796.80.29
Valvular disease2.557.194.293.30.27
Pericarditis3.261.193.892.80.32
Claudication1.830.099.598.20.37
Minor tissue loss0.90.099.398.40.01
Significant tissue loss0.2100.099.698.80.58
Venous thrombosis4.262.593.091.70.35
Gastrointestinal infarction0.450.099.193.00.32
Mesenteric insufficiency0.70.097.399.60.01
Gastrointestinal stricture/surgery0.40.096.596.10.01
Pancreatic insufficiency0.20.099.599.30.02
Muscle atrophy4.436.194.191.60.23
Deforming arthritis7.471.481.881.00.03
Osteoporotic fracture4.953.697.295.10.49
Avascular necrosis3.742.999.194.20.44
Osteomyelitis0.750.099.198.80.36
Ruptured tendon1.257.195.695.10.21
Alopecia11.239.186.781.40.22
Scarring3.283.387.187.00.25
Premature gonadal failure6.058.893.891.70.42
Malignancy6.08.899.694.60.54
Diabetes mellitus3.57096.996.00.53

Table 4 shows the total and domain scores for the SDI completed by rheumatologists and the LDIQ completed by SLE subjects. Subjects scored more positively than their physicians for every domain of the SDI. Correlation coefficients between the SDI and the LDIQ scores were generally good, and highest for the ocular, cardiovascular, malignancy, and diabetes mellitus domains.

Table 4. Total and domain scores for the 14 rheumatologist-completed SDIs and 569 subject-assessed LDIQs in stage 2*
Damage domainRheumatologists, mean ± SDSubjects, mean ± SDSpearman's correlation coefficient
  • *

    SDI = Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index; LDIQ = Lupus Damage Index Questionnaire.

Ocular0.14 ± 0.380.21 ± 0.460.60
Neuropsychiatric0.28 ± 0.570.72 ± 1.070.42
Renal0.15 ± 0.450.50 ± 0.790.46
Pulmonary0.09 ± 0.330.28 ± 0.700.44
Cardiovascular0.15 ± 0.450.29 ± 0.670.54
Peripheral vascular0.08 ± 0.300.14 ± 0.450.42
Gastrointestinal0.07 ± 0.280.14 ± 0.450.25
Musculoskeletal0.28 ± 0.690.48 ± 0.860.44
Integument0.14 ± 0.390.31 ± 0.610.24
Gonadal0.06 ± 0.240.09 ± 0.290.42
Malignancy0.06 ± 0.240.08 ± 0.300.66
Diabetes mellitus0.04 ± 0.180.05 ± 0.230.56
Total score1.53 ± 1.803.30 ± 3.150.50

Stage 3: NDB mail-based validation

Six hundred five NDB SLE participants, mainly white women, whose demographics are shown in Table 1 (90% of those mailed), returned the LDIQ. Twenty-three percent were currently receiving US Social Security disability benefits, 42.3% had received disability payments at some time in their lives, and 27.6% considered themselves disabled. Agreement between the LDIQ and the SDI was lower in this community-based part of the study (mean agreement 81%) (Table 1) than in the office-based samples.

LDIQ score distribution and component items

The LDIQ was skewed to the right. The mean ± SD score was 4.9 ± 3.5 (range 1–22), the median (interquartile range) was 4.0 (2.0–6.0), and the alpha reliability was 0.72. The major contributions to the LDIQ total score were from the neuropsychiatric and musculoskeletal domains (Figure 1). Neuropathy was the most commonly reported item (35%). The next most common item (34.4%) was arthritis in the hands. Cataracts were noted by 32.4%. Because Figure 1 indicated substantial differences in the degree to which individual domains contributed to the LDIQ total scores, we investigated the relationship between the degree of contribution of the individual domains and 2 SLE outcomes. Table 5 shows that the neuropsychiatric and musculoskeletal domains, which contributed most to the LDIQ total score, were also the most strongly associated domains with disability status and the SF-36 PCS.

thumbnail image

Figure 1. Contributions of individual domains to the total Lupus Damage Index Questionnaire score. GI = gastrointestinal.

Download figure to PowerPoint

Table 5. Spearman's correlation coefficients between the LDIQ, comorbidity index, patient's global and important outcome, and status variables in SLE among 605 participants in the National Data Bank for Rheumatic Diseases*
VariableLDIQComorbidity indexPatient global
  • *

    LDIQ = Lupus Damage Index Questionnaire; SLE = systemic lupus erythematosus; SF-36 = Short Form 36; MRC = Medical Research Council; SLAQ = Systemic Lupus Erythematosus Activity Questionnaire; HAQ DI = Health Assessment Questionnaire disability index.

  • Not significant at P ≤ 0.05.

LDIQ score (range 0–22)1.0000.4460.166
Comorbidity index (range 0–9)0.4461.0000.150
SF-36 physical component score0.4320.3130.453
MRC dyspnea scale (range 1–5)0.3970.3430.324
Disability0.3710.2720.275
SLAQ score (range 0–37)0.3670.3390.351
Procedure and outpatient costs (US$)0.3610.2540.214
Pain (range 0–10)0.3110.2580.681
Total direct medical costs (US$)0.2960.2420.232
Disease duration, years0.2890.1510.018
Household income (US$)0.2540.1710.138
Total hospital costs (US$)0.2330.1160.135
No. of hospitalizations0.2120.1060.131
Prednisone, %0.2090.1210.067
Fatigue (range 0–10)0.2010.1760.654
Global (range 0–10)0.1660.1501.000
HAQ DI (range 0–3)0.1600.1220.603
SF-36 mental component score0.1410.1620.237

Association between the LDIQ and SLE outcomes

We studied the relationship between the LDIQ, the comorbidity index, and patient global in relation to important SLE outcome and status variables using Spearman's correlations (Tables 5 and 6). The LDIQ was significantly (P < 0.001) associated with important outcome and status variables. As hypothesized, the association between the LDIQ and clinical variables was stronger in all cases than the association between the comorbidity index and these variables (Table 5). The strongest correlates of LDIQ were the comorbidity index (r = 0.45), the SF-36 PCS (r = 0.43), the Medical Research Council dyspnea scale (r = 0.40), disability status (r = 0.37), and prior SLAQ score (r = 0.37). By contrast, patient's global status, a measure of current status, was correlated with the LDIQ at 0.17 and with the comorbidity index at 0.15.

Table 6. Strength of association between the LDIQ score/domains and disability status and the SF-36 PCS score as measured by Kendall's tau-a among 605 participants with SLE in the National Data Bank for Rheumatic Diseases*
Score/domainDisabilitySF-36 PCSLDIQ
  • *

    LDIQ = Lupus Damage Index Questionnaire; SF-36 = Short Form 36; PCS = physical component summary; SLE = systemic lupus erythematosus.

  • All associations are significant at P < 0.001.

  • Not significant at the 0.05 level.

LDIQ total score0.191−0.294
Neuropsychiatric0.151−0.2470.356
Musculoskeletal0.119−0.2010.363
Integument0.061−0.0680.233
Cardiovascular0.059−0.0860.262
Gastrointestinal0.047−0.0960.121
Pulmonary0.046−0.0720.171
Renal0.0450.0240.179
Gonadal0.041−0.0060.073
Diabetes mellitus0.039−0.0800.100
Peripheral vascular0.039−0.0600.141
Ocular0.033−0.0670.204
Malignancy−0.008−0.0080.052

To assess the association between the LDIQ and outcomes quantitatively, we studied the 4 quartiles of LDIQ scores in relation to direct medical costs, work disability, the comorbidity index, and hospitalization with the last 6 months. As shown in Table 7, increasingly abnormal outcomes were associated with the quartiles of the LDIQ score. The P value for linear trend for each variable was <0.001.

Table 7. SLE outcomes and quartiles of the LDIQ among 605 participants in the National Data Bank for Rheumatic Diseases*
LDIQ quartile (range)Semiannual medical costsDisability, %Comorbidity indexHospitalized in the last 6 months, %
  • *

    P < 0.001 for linear trend. SLE = systemic lupus erythematosus; LDIQ = Lupus Damage Index Questionnaire.

1 (1–2)$2,7128.51.98.5
2 (3–4)$4,21720.62.514.6
3 (5–6)$4,89735.43.218.6
4 (7–22)$6,36351.73.829.1

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

The purpose of this study was to develop, refine, and perform the initial validation of a subject self-assessed LDIQ in a large English-speaking population of SLE patients. We found good overall agreement between the newly developed LDIQ and the SDI. In the community-based NDB stage 3 of this study, in which participants completed the questionnaire by mail rather than in the rheumatologist's office, the mean agreement was slightly lower at 82%, suggesting that physicians and patients may have had some influence on each others' responses. The specificities of the individual LDIQ items were generally greater than 80% compared with the SDI results. Sensitivities were variable and were lower for low prevalence damage items, such as myocardial infarction, mesenteric insufficiency, GI stricture or surgery, and pancreatic insufficiency (all of which had <1% prevalence). The low prevalence of certain types of damage does limit the interpretation of comparisons of the 2 instruments. Correlations between the SDI and the LDIQ instruments were high for most organ damage domains in both the office-based and mailed validation studies. This suggests that the LDIQ may be a useful and reliable alternative to the SDI in assessing SLE-related damage in population studies.

In developing this index, we expected a moderate degree of disagreement between physicians and patients regarding specific damage questions. For physicians, overreporting should not occur, but underreporting might occur. For example, specialty lupus physicians might be unaware of diagnoses made by other physicians, might have out of date records, or might not adequately examine the eyes for cataracts or retinal damage. Such underreporting might be a major problem when general physicians, not lupus specialists, provide data. More important, however, is misreporting by patients. Although subject underreporting would be expected for some items, because the subjects may not have had or understood all of the data that physicians had, overreporting was the more common misclassification. Questions concerning end-stage renal disease, cognitive impairment, alopecia, skin scarring, claudication, retinal changes, muscle atrophy, and osteomyelitis, which were confusing to subjects or that showed high disagreement with clinicians' responses in the pilot study, were subsequently refined and did show improved performance in the validation study. Overall, we found the patient damage score to exceed the physician score by 1.9 units and the correlation between patient and physician damage scores to be 0.65.

The subjects in the first 2 stages of this study were consecutive, willing, English-speaking patients in major SLE centers. They were relatively young (mean age in the early 40s), with a mean disease duration of more than 10 years, the SDI scores ranging from 0 to 9, and a wide variety of SLE manifestations (Tables 1 and 3). Nonrandom subject refusal could have introduced a selection bias or limited the generalizability of the results. Stage 3 involved community-based patients, which improves the generalizability of the study. Although we targeted an eighth-grade reading level, given the complicated manifestations of SLE, many of the challenging words exceeded this level (e.g., pulmonary hypertension, claudication, cardiomyopathy, and pericarditis). We placed these terms in quotes, aiming for patients' recognition. When stratified by the participants' educational level, correlations with the rheumatologists' SDI scores were actually higher among subjects with fewer years of formal education.

One limitation of this validation study is that the LDIQ was assessed using responses of subjects' physicians on the SDI as the gold standard. The assumption was that the physicians' responses were correct, but this may not have always been true. As our analyses suggested, this is particularly likely for subjects who have had SLE for many years and had some of their SLE-related damage early in their disease (possibly before they were known to their current physician). The SDI was validated and endorsed by the ACR in 1996 (6), and has since been validated in a number of international centers representing different health care systems (6, 10, 13). These studies have demonstrated that this instrument can reliably identify changes in damage seen in both active and inactive disease and that, at one point in time, there is no correlation between the SDI score and disease activity, measured by the Systemic Lupus Erythematosus Disease Activity Index (a disease-activity scale), or health-related quality of life, measured by the Medical Outcomes Survey Short Form 20 (6, 10, 32, 33). The SDI therefore functions as intended, measuring accumulated damage in patients with SLE independent of simultaneous disease activity and/or health-related quality of life (although these 3 facets of disease are inextricably linked, as with progression over time) (15–17). Higher scores on the SDI are predictive of poor outcomes, defined as death or hospitalization (34–36). African Caribbean, African American, Hispanic, and Asian patients accumulate more damage as assessed by the SDI than do white patients (12, 37), suggesting a racial/ethnic influence on the expression of this disease. SDI-assessed damage clearly increases with disease duration (38). The SDI therefore provides an important outcome measure in SLE, both for studies of prognosis and in the assessment of the long-term effects of the disease process and its medical therapy. Whether the self-assessed LDIQ will be predictive of long-term clinical outcomes and mortality in the same way as the SDI will be the subject of future investigation. Age, disease duration, and race/ethnicity have known influences on the severity of SLE-related damage and are also likely to influence the subjects' understanding of their disease and the questionnaire.

If the purpose of the LDIQ is to evaluate an individual patient, the level of concordance that we found would be unacceptable. However, if the purpose is to evaluate groups of patients in outcomes research, particularly in community settings, the degree of concordance is acceptable if the damage scale is substantially predictive of health status and outcomes. Data from stage 3 of this study, the observational cohort, suggests this is the case. In this community-based cohort study, the LDIQ was more useful for identifying health status and outcomes than standard assessment measures. In this setting, the higher LDIQ value of 4.9 compared with 3.4 likely reflects increased age, SLE duration (39), and other characteristics of the NDB cohort. It is possible that patients followed in academic lupus centers are more educated about SLE (regardless of educational level) than are community patients, and therefore more likely to answer the questions correctly, as suggested by the lower agreement between physician and patient scores in this cohort. Regression analyses on age and SLE duration (data not shown) indicated that approximately 0.8 units of the 4.9 LDIQ score in the current study can be accounted for by age and SLE duration. Both of the variables have been shown to be associated with increased damage, as measured by the SDI (39, 40). Correlations between SLE disease activity (by the SLAQ) and the LDIQ were as good as those between the SLAQ and patient comorbidity index and patient global assessment. As shown in Table 5, the LDIQ is a “better” comorbidity index than the standard comorbidity index with respect to outcomes that can be considered fixed or relatively fixed. Similarly, the LDIQ is less correlated with patient activity variables like fatigue and HAQ than the patient global. This is not surprising because the LDIQ measures the domain of damage, which is conceptually different than the disease activity domain. The data in Table 5 suggest that the LDIQ is performing as expected in these cross-sectional analyses. In one study of 54 SLE patients, the SDI was correlated with the SF-36 PCS, SF-36 MCS, and patient global at values of 0.34, 0.02, and 0.14, respectively (41). In the current report, the LDIQ correlation with these variables was 0.432, 0.141, and 0.166, respectively, suggesting similar, or perhaps stronger, associations between the LDIQ and self-reported patient variables compared with the SDI data.

We have also found that stepwise increases in the LDIQ were associated with clinically important increases in direct medical costs, work disability, comorbidity, and hospitalization (Table 7). We also noted in Figure 1 that different domains contributed different amounts to the final LDIQ score. We noted that the 2 domains that contributed the most to the LDIQ were also the domains most strongly associated with disability status and health status (Table 6). The associations with the other domains were weaker, reflecting the uncommonness of some of the outcomes, that many of the outcomes are also common in individuals without SLE, and the weighting design of the SDI authors. However, attempts to reweight the SDI after the use of Rasch analysis have shown the current weighting system to be clinically appropriate (42).

The LDIQ has been translated into several languages. In one validation study, a total of 887 SLE patients and 40 rheumatologists with a special interest in SLE participated: 659 of the patients completed the Spanish version (611 in Latin America, 30 in the US, and 18 in Spain), 140 completed the Portuguese version (122 in Brazil and 18 in Portugal), and 88 completed the French version (all in Canada) of the LDIQ as well as the SDI (43). In that study, the SDI total score was 1.9, the LDIQ total score was 3.7, and the correlation between the LDIQ and the SDI was 0.61.

Quantifying irreversible organ damage from SLE is important for characterization of SLE populations and for outcomes research. The results of this study are encouraging and suggest that the LDIQ, a self-reported questionnaire completed by patients rather than physicians, may be able to reliably assess SLE-related damage in patients, providing an alternative to the physician-completed SDI for patients with lupus who are primarily managed in the community rather than in specialist lupus centers. Physicians caring for SLE patients in the community may not be familiar with the use of this assessment tool, nor have the time or motivation to complete it. This currently limits the use of the SDI to large academic specialist centers, thus the generalizability of research findings to these settings. Although it may not be possible to use these 2 instruments interchangeably within the same study, the LDIQ could be employed for future studies where the collection of physician-assessed data is impossible, ultimately allowing the expansion of investigations of the impact of SLE beyond academic medical centers. The LDIQ has preliminary validity, but comparative longitudinal studies will be required to determine its reliability, sensitivity to change over time, and real value in assessing organ damage from SLE in cohort studies.

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published. Dr. Costenbader had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study conception and design. Costenbader, Karlson, Katz, Chakravarty, Liu, Alarcón, Wolfe.

Study conception and design. Costenbader, Karlson, Katz, Chakravarty, Liu, Alarcón, Wolfe.

Acquisition of data. Costenbader, Khamashta, Ruiz-Garcia, Perez-Rodriguez, Petri, Elliott, Manzi, Turner-Stokes, Bermas, Coblyn, Massarotti, Schur, Fraser, Navarro, Hanly, Shaver, Katz, Chakravarty, Fortin, Sanchez, Liu, Michaud, Alarcón, Wolfe.

Analysis and interpretation of data. Costenbader, Karlson, Turner-Stokes, Massarotti, Schur, Katz, Michaud, Alarcón, Wolfe.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

The authors are grateful to Victoria Gall for her help in translating the SDI into lay language, to Amy Yearout for her technical assistance, and to Leigh Fritz for her efforts recruiting subjects.

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  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information
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Supporting Information

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. Acknowledgements
  9. REFERENCES
  10. Supporting Information

Additional Supporting Information may be found in the online version of this article.

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ACR_20193_sm_appendix.pdf93KSUPPLEMENTAL APPENDIX

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