Analysis of the correlation between disease activity score 28 and its ultrasonographic equivalent in rheumatoid arthritis patients

OBJECTIVE

To study the differences between disease activity score 28 (DAS28) index and an ultrasound (US) approach using index echographic disease activity score (ECODAS).

METHODS

This was a cross-sectional study in patients diagnosed with rheumatoid arthritis (RA). Demographic, clinical, and laboratory data were collected. We created a US index (ECODAS) evaluating the joints with synovitis using gray scale US (GSUS) and power Doppler US (PDUS) and calculated the formula of DAS28 index with both variables substituting tender joint for GSUS and swollen joint for PDUS (ECODAS1) and vice versa (ECODAS2).

RESULTS

A total of 58 patients (65.5% women and 34.5% men) were included in the study. There was no significant difference between the 2 US indexes. We obtained a Pearson's correlation coefficient (Pearson's r) of 0.56 (p<0.00001) between DAS28 and ECODAS1 and of 0.57 (p<0.00001) between DAS28 and ECODAS2, respectively. However, for patients with a high disease activity [DAS28>5.1, tender joint count (TJC, high)], the correlation was poor (0.18) and ECODAS indexes were significantly lower (p=0.001). The correlation increased (0.86, p<0.001) when we excluded the tender joints and the joints with GS-positive synovitis in both the scores.

CONCLUSION

US reduces the bias in the evaluation of patients with RA with a high value in DAS28 index. We found a clear difference between DAS and ECODAS when TJC was high. The results suggest that joint tenderness reported by the patient is not a good reflection of inflammation. More studies are needed to find a new combined clinical and sonographic index that would better assess the disease activity in patients with RA.