Measuring inflammation in rheumatoid arthritis with a new clinical and ultrasound index: development and initial validation

With the aim to develop and validate a clinical + ultrasound (US) inflammation score in rheumatoid arthritis (RA) for use in clinical practice, a mixed-method study was conducted. The theoretical development of the index was achieved with qualitative methodology (discussion group and Delphi survey). Subsequently, a cross-sectional study was carried out to analyse issues related to scoring and validation of the new index. RA patients underwent clinical [28 swollen and tender joints count, patient and physician global assessment (PhGA), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP)], and US assessments [synovitis or tenosynovitis by grey-scale (GS) and power Doppler (PD) of 42 structures]. An index was created based on statistical models and expert interaction. Construct validity was tested by correlation with DAS28, SDAI, CDAI, and PhGA. Reliability was evaluated in a subgroup of patients with the intraclass correlation coefficient (ICC). US assessment, CRP, and swollen joints were the items that passed the prioritization phase (Delphi study). For the cross-sectional study, 281 patients were randomly divided into design (n = 141) and validation samples (n = 140). The combination of US sites chosen (7 bilaterally) detected the maximum proportion of synovitis and PD present. Three scoring methods were tested: semiquantitative (0–3 GS + 0–3 PD), dichotomous (0/1 GS + 0/1 PD), and qualitative (0/1 based on algorithm). All showed strong correlation with activity measures (ρ ≥ 0.60), and reliability (ICC 0.89–0.93). The index with best parameters of validity, feasibility, and reliability was the qualitative. The final index chosen was the sum of swollen joint count, US qualitative score, and CRP. The UltraSound Activity score is a valid and reliable measure of inflammation in RA equal to the sum of 28 SJC, a simplified (0/1) US assessment of 11 structures and CRP. It is necessary further investigation to demonstrate additional value over existing indices.