Background According to previous studies, serum amyloid A (SAA) is involved in the pathophysiology of several conditions including inflammatory arthritis and psoriasis. Recent evidence suggests its valuable role in monitoring disease activity in Rheumatoid Arthritis, but its role is yet to be determined in Psoriatic Arthritis (PsA).
Objectives To study the association between SAA levels and its variation with other biomarkers and disease activity/functional parameters in a cohort of PsA patients under biologic therapy.
Methods Observational retrospective study was conducted including PsA patients (according to CASPAR criteria) followed at our Rheumatology department with at least one measurement of SAA levels from January 2015 until December 2016. Demographic and clinical data were obtained by consulting the national database (Reuma.pt). The disease activity/functional scores from at least one visit and corresponding measurements of SAA, ESR and CRP levels were collected. The difference (Δ) between 2 evaluations separated by a median time of 6 months [6–18] was calculated for all variables. Agreement between dichotomized biomarkers was calculated using kappa coefficients. Correlations were studied using Pearson and Spearman coefficient analysis. Significance level was set as 0.05.
Results 53 PsA patients were included. 31 (59%) patients were females with a mean (SD) age of 50 (11.2) years and a median disease duration of 9 years [1–43]. 28% had axial involvement, 34% peripheral involvement and 38% had both types. All patients were under biologic DMARD. 100 SAA measurements were collected. Median SAA and ESR levels were significantly superior in female patients (23 vs 6mm/1sth and 8.6 vs 4.4mg/L, respectively, p<0.05) and only ESR levels correlated with age (r=0.20, p=0.05). The three biomarkers showed a weak association with serum creatinine levels, with greater correlation for SAA (r=0.46, p<0.001). SAA levels had a stronger correlation with CRP (r=0.75, p<0.001) than with ESR levels (r=0.26, p<0.01). SAA and CRP (dichotomized as negative/positive) had a greater level of agreement (κ=0.40) compared to ESR (κ=0.26 and κ=0.32, respectively). No significant correlations were found between the biomarkers and the tender/swollen joint count or the pain/global disease activity VAS. SAA levels correlated with ASDAS CRP (r=0.43, p<0.001) and weakly with ASDAS ESR and DAS28 CRP (r=0.20 and r=0.24, respectively, p<0.05). Only ESR had a significant weak correlations with BASDAI, MASES and SPARCC scores (r=0.25, r=0.21, r=0.35; p<0.05). All the biomarkers had weak correlations with BASFI and HAQ scores. ΔSAA levels had a weak correlation with ΔCRP (r=0.32, p=0.03; n=47) and no significant association was found with ΔESR. ΔSAA correlated significantly with ΔASDAS CRP and ΔBASMI (r=0.32, r=0.39; p<0.05).
Conclusions This study showed that SAA levels and its variation had a significant correlation with CRP levels and its variation, respectively. Significant association with ASDAS CRP variations suggests that serial measurements of SAA may represent an additional marker for monitoring disease activity over time in PsA patients.
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Disclosure of Interest None declared
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