Simple Disease Activity Index (SDAI) for Rheumatoid Arthritis

Monitoring RA with the Simple Disease Activity Index (SDAI)

The SDAI is a simple to use scoring system that focuses on the main symptoms of rheumatoid arthritis and that has been validated for both research and clinical use. Therapeutic areas for the SDAI include skin and connective tissue diseases, musculoskeletal disease and immune system diseases.

The SDAI score helps clinicians determine the severity of rheumatoid arthritis based on clinical and laboratory data, so consists of the sum of the components: SJC + TJC + CRP + PGA + EGA

Where:

• SJC – Swollen Joint Count
• TJC – Tender Joint Count
• CRP - C-reactive protein in mg/dL
• PGA – Patient Global Assessment of Disease Activity
• EGA – Evaluator Global Assessment of Disease Activity

Patients with high scores should receive early and aggressive medication and be closely monitored. It is considered that attaining low or remission levels may prevent disease progression and further disability.

Compared to other scores, the SDAI has shown the highest sensitivity and specificity in predicting physicians’ therapeutic decisions.

Remission is considered when SDAI is up to 3.3 whilst response to therapy is considered moderate if SDAI decreases by more than 7 points and major if the decrease is of more than 17 points.

In the original study by Smolen et al., the SDAI was shown to provide a valid and sensitive assessment of disease activity and treatment response, one that for rheumatoid arthritis, is comparable with the DAS 28 response criteria.

The SDAI was defined as the numerical sum of five outcome parameters, assessment of 28-joints to provide a tender and a swollen joint count, two visual analogue scales (one for patient and one for physician) and the lab result of the level of C-reactive protein.

The mean SDAI calculated for patients at baseline was 50.06, 50.55 and 43.20 in three trials and was correlated with a high level of statistical significance to the DAS 28 and HAQ scores at baseline, endpoint and change at endpoint.

The index was further validated by comparing the SDAI scores with survey results obtained from evaluations of disease activity performed by rheumatologists in test cases.

Analysis of physician responses showed significant association between the perception of disease activity and subsequent total SDAI score.

References

Original reference

Smolen JS, et al. A simplified disease activity index for rheumatoid arthritis for use in clinical practice. Rheumatology. 2003; 42 (2): 244-257.

Validation

Aletaha D, Smolen JS. The Simplified Disease Activity Index (SDAI) and Clinical Disease Activity Index (CDAI) to monitor patients in standard clinical care. Best Pract Res Clin Rheumatol. 2007; 21(4):663-675.

Other references

Soubrier M, Zerkak D, Gossec L, Ayral X, Roux C, Dougados M. Which variables best predict change in rheumatoid arthritis therapy in daily clinical practice? J Rheumatol. 2006; 33(7):1243-6.