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Ann Rheum Dis. Author manuscript; available in PMC Sep 13, 2010.
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PMCID: PMC2937022
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EULAR Sjogren's syndrome disease activity index: development of a consensus systemic disease activity index for primary Sjogren's syndrome

Abstract

Objective

To develop a disease activity index for patients with primary Sjögren’s syndrome (SS): the European League Against Rheumatism (EULAR) Sjögren’s Syndrome Disease Activity Index (ESSDAI).

Methods

Thirty-nine SS experts participated in an international collaboration, promoted by EULAR, to develop the ESSDAI. Experts identified 12 organ-specific “domains” contributing to disease activity. For each domain, features of disease activity were classified in 3 or 4 levels according to their severity. Data abstracted from 96 patients with systemic complications of primary SS were used to generate 702 realistic vignettes for which all possible systemic complications were represented. Using the 0–10 physician global assessment (PhGA) scale, each expert scored the disease activity of 5 patient profiles and 20 realistic vignettes. Multiple regression modelling, with PhGA used as the dependent variable, was used to estimate the weight of each domain.

Results

All 12 domains were significantly associated with disease activity in the multivariate model, domain weights ranged from 1 to 6. The ESSDAI scores varied from 2 to 47 and were significantly correlated with PhGA for both real patient profiles and realistic vignettes (r=0.61 and r=0.58, respectively, p<0.0001). Compared to 57 (59.4%) of the real patient profiles, 468 (66.7%) of the realistic vignettes were considered likely or very likely to be true.

Conclusion

The ESSDAI is a clinical index designed to measure disease activity in patients with primary SS. Once validated, such a standardized evaluation of primary SS should facilitate clinical research and should be helpful as an outcome measure in clinical trials.

Keywords: primary Sjogren's syndrome, outcome assessment, systemic features, activity index, clinical vignettes, disease activity

Primary Sjögren’s syndrome (SS) is a systemic disorder characterized by lymphocytic infiltration and progressive destruction of exocrine glands. The inflammatory process can, however, affect any organ. As a result, clinical features can be divided into two facets: (i) benign but disabling manifestations such as dryness, pain and fatigue, affecting almost all patients; and (ii) severe systemic manifestations that affect 20% to 40% of patients.

Evidence-based therapy for SS is largely limited to treatments that improve sicca features.[1] Clinical trials of disease-modifying therapies have used a variety of ad hoc outcome measures mainly based on glandular features or patient symptoms, but not systemic features.[26] Valid activity indexes are needed [79] to assess the effectiveness of new targeted therapies, such as B-cell targeted therapies that have shown promising results for both severe systemic [10, 11] and glandular features.[1215] Two disease activity indexes have recently been proposed: the SS disease activity index (SSDAI) [16] and the Sjögren’s Systemic Clinical Activity Index (SCAI).[17] The development of these indexes was based on exploratory studies conducted in single countries, but they serve as the basis of the present collaborative project. Thus, the European League Against Rheumatism (EULAR) has promoted an international collaboration to develop consensus disease activity indexes. Two indices are currently in development: (i) a patient-administered questionnaire to assess patient symptoms, the EULAR Sjögren’s Syndrome Patient Reported Index (ESSPRI); and (ii) a systemic activity index to assess systemic complications, the EULAR Sjögren’s Syndrome Disease Activity Index (ESSDAI).

We now describe the development and initial validation of the ESSDAI. This index was developed with the help of a worldwide panel of primary SS experts using physician global assessment (PhGA) of disease activity as an external criterion. The aim is for the ESSDAI to be used as outcome criteria to evaluate primary SS in a standardized way in both clinical trials and daily practice.

METHODS

This paper results from a collaboration of experts identified through their involvement in the primary SS field, headed by a steering committee of 7 physician experts in SS (HB, SB, JEG, XM, ET, AT, CV), a clinical epidemiologist (PR) and a rheumatologist, a fellow in clinical epidemiology (RS). The research protocol was endorsed by EULAR (project code CLI 010).

The steps of the development of the ESSDAI are summarized below; the entire methodology is available online (Appendix 1).

Selection of relevant domains and definition of items

Domains of organ-specific involvement relevant to assess disease activity were selected in these steps. For each domain, the different clinical manifestations were ranked by level of activity (i.e., items). For selection of domains relevant to disease activity and definition of items for each domain, steering committee members prepared a preliminary proposal on the basis of their clinical experience, literature review and previous work.[16, 17] The preliminary selection of domains and items were successively submitted to the expert panel. Experts had to rate the importance of each domain or suggest any additional domains or changes to proposed items. Intention-to-treat was used as a help for experts to define the different activity levels that ranged from no activity (requiring no treatment) to high activity (requiring high dose steroids or immunosuppressant). The experts’ proposals were analyzed, then discussed and voted on during a meeting.

Elaboration of clinical vignettes

In this step, realistic clinical vignettes were generated from real patient profiles.

Abstraction and standardization of real patient profiles

Five members of the steering committee supplied 96 profiles of their patients with systemic complications of primary SS. Each profile had to contain sections on “History” (demographic data and past medical history), “Today” (clinical symptoms and results of imaging examination) and “Laboratory” (biological features). Patient profiles included data from the baseline and 2 follow-up visits (3 and 6 months).

Abstraction of descriptions of items from real patient profiles

From patient profiles, 96 histories and 364 items, included in the “Today” and “Laboratory” sections, were extracted and standardized by the same investigator (RS). Description of all ESSDAI items were obtained and entered in a database with their corresponding scoring (domain and activity level). Each item had a median of 8.5 (interquartile range [IQR: 4–15] descriptions.

Generation of realistic clinical vignettes

i. Determination of construction rules

Data from primary SS patient cohorts of 5 members of the steering committee (SB, XM, ET, AT, CV)[1620] were used to construct a sample of vignettes with characteristics similar to European patient cohorts.

ii. Generation of clinical vignettes

In total, 720 clinical vignettes were generated by a combination of “History” and items from the “Today” and “Laboratory” sections, with respect to the domain and item distribution defined previously. However, because items in the database referred to only systemic features, descriptors of symptoms such as dryness, pain and fatigue were generated and assigned to 30% of the patient vignettes.

Assessment

The 96 real patient profiles and the 720 clinical vignettes were randomly assigned to the 40 experts. Each expert had to rate 5 real patient profiles (rated by 2 raters each) and 20 clinical vignettes (18 were “unique” and 2 were “common” to 2 raters). For the survey, an internet-secure relational database was constructed. Patient data were presented chronologically, and the responses could not be changed. For all visits of each profile or vignette, experts had to assess disease activity by use of the PhGA on a 0–10 numerical scale and a 5-point scale (inactive, low, moderate, high, very high activity). For the first visit of each profile or vignette, they also had to evaluate the plausibility of each patient case with use of a 5-point scale (very unlikely, unlikely, possible, likely, very likely) by answering the following question: “Please indicate, according to your clinical experience and knowledge of the disease, the likelihood that this patient scenario is a real case”.

Statistical methods

Determination of domain weights and construction of the ESSDAI

Realistic clinical vignettes were used to determine domain weights. Disease activity assessed by the PhGA was used as an external criterion. Bivariate analysis involved Pearson’s correlation between PhGA and each domain separately; for each domain, scores ranged from 0 = “no activity” to 3 = “high activity”. All domains were entered into multivariate models; the PhGA was used as a dependant variable and each domain was an explanatory variable. Two models were evaluated: a multiple linear regression model and a robust regression model with the least-median-of-squares method with an MM estimator.[21, 22] The weights assigned to each domain were derived from the regression coefficients of the multivariate model and rounded to form simplified indices. The weight of each item was obtained by multiplying the weight of the domain by the level of activity.

Preliminary validation

The ESSDAI was then calculated for all real patient profiles and realistic clinical vignettes. Construct validity was assessed by the strength of correlation between the ESSDAI score and the disease activity score assigned by the expert.

Sensitivity analyses

To evaluate the stability/robustness of the domain weight estimation, other models were tested: a logistic regression model with the 5-point scale used as an external criterion and different multiple linear regression models after pooling items that clustered.

Patient profile plausibility

Evaluation of patient profile plausibility of realistic clinical vignettes was compared to that of real patient profiles by a Cochran-Armitage trend test.

Reliability of disease activity scoring

The evaluation of clinical vignettes common to 2 raters was used to assess inter-rater reliability:

  • For the 0–10 PhGA: intraclass correlation coefficient (ICC) and Bland and Altman graphical analysis[23, 24]
  • For the 5-point scale: global agreement and Kappa statistics[25, 26]

The evaluation of real patient profiles was used to assess intra-rater reliability by the ICC, if at the first follow-up visit, the physician considered the disease activity unchanged. ICC confidence intervals were estimated with bootstrapping methods, with 1000 replications.[27]

For all statistical analyses, a p-value less than 0.05 was considered statistically significant. All statistical analyses involved use of SAS release 9.1 and R release 2.2.1 statistical software packages.

RESULTS

Characteristics of expert panel

Of 40 invited primary SS experts, 39 took part in the study (35 Europeans from 13 countries and 4 North Americans). The median age of experts was 49 [IQR: 46–58] years; 35 were rheumatologists, 3 were internists and 1 was an oral medicine practitioner. All but 2 (94.9%) had ≥10 years of experience in managing primary SS. All were involved in clinical research, and 23 (59.0%) were also involved in basic science research into primary SS.

Selection of domains and definition of items

All 10 domains (constitutional and lymphadenopathy, glandular, articular, cutaneous, pulmonary, renal, muscular, peripheral nervous system, central nervous system, hematological) proposed by the steering committee were included. Experts decided to divide the “constitutional and lymphadenopathy” domain into 2 domains and to add a biological domain but not add a hepatic domain (considered to result from damage). The definition of the different activity levels (items) of each domain was obtained by consensus after discussion during meetings of the steering committee and experts.

Characteristics of real patient profiles and realistic vignettes

Thirty-nine of the 40 experts completed the rating of the 96 real patient profiles and 702 of the 720 clinical vignettes (Table 1). Real patient profiles, selected for the extent of systemic involvement, had a significantly higher number of involved organs than did realistic clinical vignettes (2.83 ± 1.46 vs. 2.14 ± 1.08; p<0.0001).

Table 1
Demographic characteristics for the 96 real patient profiles and 702 realistic clinical vignettes.

Determination of domain weights and derivation of the ESSDAI

All domains, except haematological, glandular, articular and biological domains, showed a significant positive correlation with PhGA score (Table 2). All domains were entered in 2 multivariate regression models. Multiple linear and least-median-of-squares regression models provided similar results (R2=0.29 and R2=0.30, respectively). In both models, all domains were significantly associated with disease activity (PhGA), and the weight estimation was similar. The weights derived from the regression coefficients were rounded to obtain a simple index (Tables 2 and and33).

Table 2
Correlation between domains and disease activity, as assessed by the physician global assessment (PhGA) scale, and regression coefficients and domain weights obtained with the least-median-of-squares robust regression model with an MM estimator.
Table 3
The EULAR Sjögren’s Syndrome Disease Activity Index (ESSDAI): Domain and item definitions and weights.

Preliminary validation of the ESSDAI in real patient profiles and realistic vignettes

The mean ESSDAI scores were 15.48±9.16 and 9.04±6.43 for real patient profiles and realistic vignettes, respectively. ESSDAI scores were significantly correlated with the PhGA score (r=0.58 for realistic vignettes and r=0.61 for real patient profiles, p<0.0001; Figure 1). The maximum theoretical ESSDAI score is 123; however, only 25% of realistic vignettes and the real patient profiles had a score ≥13 and ≥21, respectively. The highest score was 42 and 47 for the realistic vignettes and real profiles, respectively (Figure 1).

Figure 1
Distribution of ESSDAI scores and correlation with disease activity in real patient profiles and realistic vignettes

Sensitivity analyses

Other models for testing sensitivity analyses led to similar domain weights and similar correlation with the PhGA score.

Patient profile plausibility

Overall, experts considered 468 (66.7%) of the 702 vignettes likely or very likely to be true, as compared with 57 (59.4%) of the 96 real patient profiles (p=0.09).

Reliability of disease activity scoring

Inter-rater reliability assessed by the ICC on 76 common vignettes was 0.41 [0.18–0.60] for the PhGA. Bland and Altman graphical analysis revealed no systematic errors (mean difference=−0.16) but a variability of rating among experts (95% agreement interval [−4.92 to +4.61]). The ratings of the same vignette by 2 different experts differed by ≤1 point for 37 vignettes (48.7%), by 2 to 3 points for 30 (39.5%), and by >3 points for 9 (11.8%). The weighted Kappa statistic for disease activity rating by the 5-point scale was 0.32 [0.18–0.47]. When grouping the highest activity scores (high and very high activity) and the lowest scores (inactive, low and moderate activity), the observed agreement was 72.4% and the Kappa coefficient 0.42 [0.21–0.63].

Intra-rater reliability of the PhGA for 20 real patient profiles with unchanged activity at the first follow-up visit as assessed with the ICC was 0.86 [0.68–0.94].

DISCUSSION

The ESSDAI is a consensus clinical index designed to measure disease activity in patients with systemic complications of primary SS. This index is modelled on physician’s judgment of disease activity. It results from a large collaboration of European and North American experts in primary SS. Compared to the PhGA, the ESSDAI performed satisfactorily for evaluation of disease activity in primary SS.

In the absence of an available “gold standard” or true understanding of disease process, the most accurate and meaningful method of disease activity assessment is to attempt to model the physician judgment. But any scale quantifying physician judgment of disease activity is a simplification of a complex mental process. For that purpose, 2 main gold standards have been used in the development of disease activity indexes: (i) the PhGA [2830] and (ii) the intention-to-treat approach.[31, 32] The PhGA was used for the development of the systemic lupus disease activity index (SLEDAI) in systemic lupus erythematosus (SLE),[2830] whereas the intention-to-treat approach was used for the development of the British Isles lupus assessment group (BILAG) for SLE [31] and the disease activity score (DAS) for rheumatoid arthritis (RA).[32] However, unlike RA that quasi-exclusively affects articular system and where therapeutic decision is reproducible, the multisystemic nature of primary SS make therapeutic decision more variable. In addition, evidence-based therapeutic management of SLE is currently more advanced than in primary SS. Moreover, in the BILAG, this approach was used to define, in each domain, the different classes (A, B, C, D, E) and not as “gold standard” to determine domain weights. Therefore, in the absence of effective treatment or consensual therapeutic management and because of the variability of physician habits, the intention-to-treat approach might be more difficult to apply as a gold standard for primary SS at this time.

In addition, the extent to which each organ involvement or patient symptoms of fatigue and pain can influence the physician’s evaluation of disease activity, in such a polymorphous disease, is extremely variable, as demonstrated by the limited reliability of the PhGA. These discrepancies among physicians’ views, even among disease experts, justify the necessity for a more objective and standardized scoring system to homogenise assessment of disease activity in different settings, by different physicians, experts but also less experienced physicians. Similar to correlation of SCAI scores with the PhGA, [17] that of ESSDAI scores with the PhGA was about 0.60. These correlations were lower than that from other studies evaluating disease activity scores for various systemic disorders [16, 29, 33]. However, in most of these studies, the experts involved were trained to the rating of the PhGA and the different activity tools to improve reliability and homogeneity of this scoring. In the present study, to be closer to usual practice, we decided not to perform a training exercise.

The ESSDAI was developed by a large panel of primary SS experts and attempted to reflect their thought process. This may have ensured the content validity of the ESSDAI, including all relevant determinants of disease activity. The validity of the ESSDAI was further confirmed by the significant association of all domains with disease activity in our model. Previous primary SS activity indexes have been developed with use of cohorts in which about half of the patients had inactive or weakly active disease.[16, 17] Our strategy was to use data from selected patients with systemic features to generate realistic clinical vignettes. This methodology enabled us to obtain a large number of vignettes (more than would have been possible with real patients) representing all possible systemic disease involvement (i.e., items). We then evaluated the extent to which each item influenced the evaluation of disease activity, which had not been possible in previous studies that did not include all organ-specific features.[16, 17] As in all global scoring system,[16, 29] similar ESSDAI scores (same disease activity) may reflect different domains involved. As a further component of this project we will also be evaluating the most common patient-reported symptoms such as dryness, pain and fatigue in a patient-completed questionnaire the ESSPRI.

A major challenge in designing a systemic index is distinguishing between damage and disease activity. The most frequent approach, to avoid scoring damage, is to consider manifestations as active only if “new” or “worsening.” Under these scoring systems, when patients are evaluated at two time points, a persistent manifestation will not be rated at the second time point, which may cause an erroneous interpretation of improvement even though the patient’s condition has not changed. To avoid this, all ESSDAI items were defined without reference to a previous assessment, but with an advice not to rate as active stable long-lasting features related to damage.

The ESSDAI is a systemic disease activity index developed to allow a standardized evaluation of disease activity in primary SS patients. Further studies are needed to assess the reliability and sensitivity to change of the ESSDAI. Once validated, if uniformly applied, the ESSDAI might enable comparison between studies and facilitate clinical research into primary SS. After the development of the patient-completed questionnaire (ESSPRI), the use of both the ESSDAI and ESSPRI for outcome assessment in randomized controlled trials should allow for assessing all facets of the disease.

Acknowledgments

This project was supported by a grant from the European League Against Rheumatism (EULAR). We thank Maxime Dougados and Alan Tyndall for their guidance and support. We thank the EULAR house in Zurich for their hospitality and outstanding organization (Ernst Isler, Anja Schönbächler and their associates). We thanks the expert panel for their active and fruitful participation.

“The Corresponding Author has the right to grant on behalf of all authors and does grant on behalf of all authors, an exclusive licence (or non exclusive for government employees) on a worldwide basis to the BMJ Publishing Group Ltd to permit this article (if accepted) to be published in ARD and any other BMJPGL products and sublicences such use and exploit all subsidiary rights, as set out in our licence (http://ARD.bmjjournals.com/ifora/licence.pdf).”

ABBREVIATIONS

BILAG
British Isles Lupus Assessment Group
DAS
Disease Activity Score
ESSDAI
EULAR Sjögren’s Syndrome Disease Activity Index
ESSPRI
EULAR Sjögren’s Syndrome Patients Reported Index
EULAR
European League Against Rheumatism
ICC
Intraclass Correlation Coefficient
PhGA
Physician Global Assessment
ROC
Receiver Operating Characteristic
SCAI
Systemic Sjögren’s Syndrome Clinical Activity
SLE
Systemic Lupus Erythematosus
SLEDAI
Systemic Lupus Disease Activity Index
SS
Sjögren’s Syndrome
SSDAI
Sjögren’s Syndrome Disease Activity Index

*Participants of the EULAR Sjögren’s Task Force

Karsten Asmussen, Soren Jacobsen, Department of Rheumatology, University Hospital, Copenhagen, Denmark; Johannes WJ Bijlsma, Aike A Kruize, Department of Rheumatology & Clinical Immunology, University Medical Center, Utrecht, The Netherlands; Stefano Bombardieri, Rheumatology Unit, Department of Internal Medicine, University of Pisa, Pisa, Italy; Arthur Bookman, Division of Rheumatology, University of Toronto, Ontario, Canada; Hendrika Bootsma, Cees Kallenberg, Department of Rheumatology and Clinical Immunology, University Medical Center, Groningen, Netherlands Simon J Bowman, Rheumatology Department, University Hospital, Birmingham, UK, Johan G Brun, Roland Jonsson, Department of Rheumatology, Haukeland University Hospital, Bergen, Norway; Steven Carsons, Division of Rheumatology, Allergy and Immunology, Winthrop University Hospital, Mineola, USA; Salvatore De Vita, Clinic of Rheumatology, University Hospital, Udine, Italy; Nicoletta Del Papa, Department of Rheumatology, G. Pini Hospital, Milano, Italy; Valerie Devauchelle, Alain Saraux, Rheumatology Department, la Cavale Blanche Teaching Hospital, Brest, France; Thomas Dörner, Rheumatology Department, Charité, University Hospital, Berlin, Germany; Roberto Gerli, Rheumatology Unit, Department of Clinical & Experimental Medicine, University of Perugia, Italy; Jacques Eric Gottenberg, Jean Sibilia, Department of Rheumatology, University Hospital, Strasbourg, France; Eric Hachulla, Department of Internal Medicine, Claude Huriez Hospital, Lille, France; Gabor Illei, Sjögren’s Syndrome Clinic, National Institute of Dental and Craniofacial Research, Bethesda, USA; David Isenberg, Centre for Rheumatology, University College, London, UK; Adrian Jones, Rheumatology Unit, City Hospital, Nottingham, UK; Menelaos Manoussakis, Athanasios Tzioufas, Department of Pathophysiology, School of Medicine, University of Athens, Greece; Xavier Mariette, Department of Rheumatology, Bicêtre Hospital, Le Kremlin Bicêtre, France; Carlomaurizio Montecucco, Department of Rheumatology, University of Pavia, Pavia, Italy; Roald Omdal, Department of Internal Medicine, University Hospital, Stavanger, Norway; Ann Parke, Clinical Immunology Unit, Division of Rheumatology, Saint Francis Hospital and Medical Center, Hartford, USA; Sonja Praprotnik, Matjia Tomsic, Department of Rheumatology, University Medical Centre, Ljubljana, Slovenia; Elizabeth Price, Department of Rheumatology, Great Western Hospital, Swindon, UK; Manel Ramos Casals, Laboratory of Autoimmune Diseases “Josep Font”, Hospital Clinic, Barcelona, Spain; Philippe Ravaud, Raphaèle Seror, Department of Epidemiology, Biostatistics and Clinical Research, Bichat Hospital, Paris, France; Josef Smolen, Division of Rheumatology, Department of Internal Medicine III, Medical University, Vienna, Austria; Serge Steinfeld, Department of Rheumatology, Erasme University Hospital, Brussels, Belgium; Nurhan Sutcliffe, Department of Rheumatology, Barts & The Royal London Hospital, London, UK; Elke Theander, Lennart Jacobsson, Department of Rheumatology, Malmö University Hospital, Lund University, Lund, Sweden; Guido Valesini, Rheumatology Unit, Department of Clinical & Experimental Medicine, Sapienza University, Rome, Italy; Claudio Vitali, Department of Internal Medicine and section of Rheumatology, “Villamarina” Hospital, Piombino, Italy; Frederick B. Vivino, Department of Rheumatology Penn Presbyterian Medical Center, University of Pennsylvania, Philadelphia, USA.

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