Background The serum levels of the pro-inflammatory calcium-binding protein S100A12 (mainly found in neutrophil granulocytes) correlate well with clinical assessments of disease activity of patients with rheumatoid arthritis (RA). Ultrasonography (US) is a sensitive method for assessing disease activity during follow-up of RA patients and has been shown to detect residual inflammation in clinical remission.

Objectives To explore the validity of S100A12 in serum as a potential inflammatory marker by comparing the levels with the results of a comprehensive US assessment.

Methods A comprehensive study was performed in 20 RA patients (median (range) age 53 (21-78), disease duration 7.5 (1-26) years, 75 % women) (including clinical (DAS28 and questionnaires), laboratory (SR and CRP) and US examination (B-mode (BM) and power Doppler (PD) of 78 joints, 36 tendons and 2 bursae) at baseline (before starting adalimumab as their first biological drug) and after 1, 3, 6 and 12 months. Serum S100A12 was analysed by a sandwich ELISA. The changes between baseline and follow-up of US scores and laboratory markers were explored by Wilcoxon signed rank test. Spearman’s rank correlation was used for analysing the associations between inflammatory markers and US scores.

Results The patients had median (range) S100A12 levels of 49 (18-475) ng/ml at baseline, 34 (18-687) after 1 month, 23 (16-173) after 3 months, 33 (19-394) after 6 months and 40 (12-620) after 12 months, while for CRP the corresponding results were 4.5 (1-136), 2.0 (1-163), 2.5 (1-26), 2.5 (1-78) and 4.5 (1-86) mg/l and for ESR 20.0 (3-67), 13.0 (3-108), 14.5 (2-65), 14.5 (5-99), 17.5 (3-78) mmHg/h. Significantly decreased levels were found at 3 months for S100A12 (p<0.01), at 3 months for CRP (p<0.01) and at 1 and 3 months (p<0.01) for ESR (figure). Compared with the conventional inflammatory markers CRP and ESR, the neutrophil protein S100A12 had the highest correlations with the comprehensive BM and PD sum scores during the 12 months follow-up, (median (range) coefficients of 0.55 (0.35-0.78) for sum score BM and 0.45 (0.27-0.75) for sum score PD).

Conclusions S100A12 was found closer associated to the comprehensive US examinations than conventional inflammatory markers. The US scores reflect the degree of synovitis in RA patients during biologic treatment, and thus the present finding of high associations between US pathology and S100A12 shows that S100A12 is a promising serum biomarker for RA patients.

Disclosure of Interest None Declared