Background Inflammation is known to play a major role in rheumatologic disorders. Hence quantitating the degree of inflammation has become essential to tailor the treatment strategy. Traditionally used measures to assess disease activity in spondyloarthritis (SpA) are ESR, CRP, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and Ankylosing Spondylitis Disease Activity Score (ASDAS). Serum amyloid A (SAA) is an acute-phase reactant predominantly synthesized in the liver by hepatocytes in response to proinflammatory cytokines. Some studies have shown that SAA correlates with disease activity in SpA and suggest it as a valuable indicator of disease activity, however it has not been extensively used in clinical practice.
Objectives To investigate if SAA levels have better correlation with conventional clinical and serological assessments in SpA than CRP and ESR.
Methods Cross-sectional study, including SpA patients under anti-TNFα treatment at a Rheumatology Department of a Portuguese Universitary Hospital. We compared the correlation between SAA, CRP and ESR levels with BASDAI, ASDAS-CRP, ASDAS-ESR, BASFI, BASMI, swollen and tender joints counts (SJC and TJC), MASES, SPARCC, and patient global assessment, physician global assessment, total back pain, nocturnal back pain rated on a visual analogue scale (VAS). The statistical analysis was performed using SPSS 21.0 software, and p<0.05 was taken to indicate statistical significance. Correlation was calculated using the Spearman rank correlation (r).
Results 88 patients were included, 61.4% (n=54) were male. The median age was 44,0 years (range 21.0–74.6). Median disease duration was 19.0 years (2- 51.6). According to ASDAS criteria, 23 patients (26.1%) had inactive disease, 21.7% moderate disease activity, 40.9% high disease activity and 11.4% very high disease activity.
SAA levels were moderately correlated with CRP levels (r=0.51, p<0.001) and had lower correlation with ESR (r=0.36, p=0.001). There was no statistically significant correlation between SAA levels and the following parameters: physician global assessment-VAS, total back pain-VAS, nocturnal back pain-VAS, MASES, SJC and TJC. SAA levels correlated with patient global assessment-VAS (r=0.218, p=0.04) but also did ESR (r=0.277, p=0.01). There was no significant correlation between SAA and BASDAI (r=0.161, p=0.134), however CRP levels and ESR showed little correlation (r=0.232, p<0.03 and r=0.366, p<0.001).
We found statistically significant correlation between SAA levels and ASDAS-ESR (r=0.298, p=0.005), ASDAS-CRP (r=0.330, p=0.002), SPARCC (r=0.221, p=0.034), BASFI (r=0.327, p=0.002) and BASMI (r=0.262, p=0.014). CRP and ESR also showed significant correlation with BASFI, but it was weaker than that observed with SAA (r=0.285, p=0.007 and 0.310, p=0.004, respectively). ESR and CRP did not correlate with BASMI.
Conclusions This study suggests that SAA can be a valuable indicator not only of disease activity but also of damage and functional impairment, that could be introduced in clinical pratice. However more studies, with larger sample sizes, and prospective ones should be undertaken to better assess this subject.
Disclosure of Interest None declared
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