Arthritis & Rheumatism, Volume 60,
October 2009 Abstract Supplement

The 2009 ACR/ARHP Annual Scientific Meeting
Philadelphia October 16-21, 2009.


Development of the Scleroderma Disease Activity Index (SDAI)

Hudson1,  M., Julien1,  Marilyse, Baron2,  Murray, Canadian Scleroderma Research Group,  , Steele1,  Russell

McGill University, Montreal, QC
Jewish General Hospital, Montreal, QC

Purpose:

Measuring disease activity in systemic sclerosis (SSc) is necessary to provide a conceptual structure to study this poorly-defined disease and as an outcome measure for interventional studies. The purpose of this study was to develop a disease activity index for SSc.

Method:

Data from a large, pan-Canadian cohort of SSc patients was reviewed. From 1800 variables available in the database, 61 were retained based on an extensive literature search and review by 2 scleroderma experts working by consensus for face and content validity. The selected variables included 54 independent variables (disease duration, disease subset, physician ID and 51 variables selected as possible indicators of disease activity in SSc) and 7 response variables. Of 745 patients entered into the registry, 191 had complete data on the abovementioned variables and were selected for this analysis. Advanced statistical methods were used to identify the best set of variables for inclusion in a new Scleroderma Disease Activity Index (SDAI).

Results:

Baseline characteristics of the patients included for the analysis were as follow: 87% female, mean age 54.5 (± 12.2) years, mean disease duration 10.7 (± 8.9) years; 39% diffuse disease. The mean physician global assessment of disease activity in the last week measured using a numerical rating scale ranging from 0–10 was 2.3 (±1.9). Lasso regression analysis using the physician global assessment of disease activity as response variable performed best and allowed the identification of 11 independent variables predictive of disease activity in SSc. Of these, 4 were patient-reported [severity of Raynaud's phenomenon (RP) in the last week measured using a numerical rating scale ranging from 0–10 (coefficient 0.21), average number of episodes of RP per week in the past month (coefficient 0.24), worsening of scleroderma in the past month (coefficient 0.24), and severity of shortness of breath in the past week measured on a numerical rating scale ranging from 0–10 (coefficient 0.33)], 4 were assessed by physicians [pulse rate per minute (coefficient 0.16), presence of basilar crackles (0.05), modified Rodnan skin score ranging from 0–51 (coefficient 0.75), and swollen joint count ranging from 0–28 (coefficient 0.16)], and 3 were lab-based [weight loss in the past year in lbs (0.13), hematocrit (coefficient 0.03) and forced vital capacity measured as percent predicted (coefficient -0.06)]. These variables accounted for 32.5% of the variance in the physician global assessment of disease activity.

Conclusion:

Using data from a large multi-centered cohort of SSc patients, we developed a new and simple measure of disease activity in SSc, the Scleroderma Disease Activity Index (SDAI), with face and content validity. Further testing is underway to verify construct validity and assess sensitivity to change.

To cite this abstract, please use the following information:
Hudson, M., Julien, Marilyse, Baron, Murray, Canadian Scleroderma Research Group, , Steele, Russell; Development of the Scleroderma Disease Activity Index (SDAI) [abstract]. Arthritis Rheum 2009;60 Suppl 10 :442
DOI: 10.1002/art.25524

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