Background There is a growing need to corroborate clinical evaluation with a more objective method as ultrasonography. At this time there is no standardized ultrasound (US) index for monitoring patients with rheumatoid arthritis (RA). The DAS28 index often does not reflect the actual situation of the patient due to bias incurred by variables such as the number of tender joints and patient global assessment.
Objectives To study the correlation between DAS28 index and the ultrasound index ECODAS. Our secondary objective is to evaluate the agreement between physical and ultrasound examination.
Methods A cross-sectional study in patients diagnosed with RA who were visited in the Rheumatology Department of our hospital, was performed. Demographics data, clinical data, in particular the evolution of the disease, the number of tender joints (NTJ), the number of swollen joints (NSJ), patient global assessment, doctor global assessment, treatment with disease modifying drugs and/or biological therapy (BT), and laboratory data (erythrocyte sedimentation rate ESR and C reactive protein CPR) were collected. For the US evaluation we used a General Electric Logiq 9 US device with a high frequency (8-13 MHz) linear transducer. The sonographer was blind to the clinical examination. We evaluated the number of joints with synovitis in gray scale (NGSUSJ) and the number of joints with Doppler signal (NPDUSJ). We defined ECODAS, an index calculated using the formula of DAS28 index, by substituting the clinical variables with sonographic ones. To decide how to use the ultrasound exam in the ECODAS index we evaluated 2 different approaches: in the first one NGSUSJ was used as an equivalent for NTJ and NPDUSJ as an equivalent for NSJ and in the second one NGSUSJ and NPDUSJ were swapped, obtaining 2 indices, ECODAS1 and ECODAS2. We also analyzed the agreement between TJ and GSUSJ and between SJ and PDUSJ, in a subgroup of patients for which we had the corresponding data.
Results We included 46 patients (69.56% women and 30.43% men) with a mean age of 61.26 years and a mean disease evolution time of 10.26. The mean ESR was 30 mm/h and the mean CRP was 0.9mg/dl. We had 31 patients treated with DMARDs, 3 with BT in monotherapy and 12 with combined therapy. The mean of the 3 indices was: DAS28 4.87, ECODAS1 4.58 and ECODAS2 4.35. In a subgroup of 36 patients the agreement between TJ and GSUSJ (69%) was significantly smaller than the agreement between SJ and PDUJ (90%). There was no significant difference between the 2 US indices. We obtained a significant r Pearson correlation coefficient of 0.51 between DAS28 and ECODAS1 and of 0.52 between DAS28 and ECODAS2. For patients with a higher NTJ a high disease activity DAS28 was obtained (>5.1). The ECODAS indices were significantly lower than DAS28 for these patients.
Conclusions ECODAS has shown a moderate correlation with DAS28 and we believe it is a good tool for monitoring patients with RA. The results suggest that joint tenderness reported by the patient is not a good reflection of inflammation. We observed that ECODAS does not significantly change by swapping the NGSUSJ and NPDUSJ. Hence, despite its moderate correlation with DAS28, it is not its US equivalent. Therefore more studies are needed in order to find a new combined clinical, laboratory and US index that would better assess the disease activity in RA patients.
Disclosure of Interest None declared
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