Associations of Platelet Count with Inflammation and Response to Anti-TNF-α Therapy in Patients with Ankylosing Spondylitis

Abstract

Background: Increased platelet count has been reported in ankylosing spondylitis (AS) patients, but its clinical significance is still largely elusive. The objective of this study was to evaluate the clinical role of platelet count in AS patients, especially its impact on treatment outcomes. Methods: A case-control study containing 35 AS patients receiving anti-tumor necrosis factor-α (anti-TNF-α) therapy and 45 healthy controls was performed, and AS patients were followed at least 6 months after anti-TNF-α therapy. A systematic review and meta-analysis of studies containing relevant data on outcomes of interest was also performed. Results: AS patients had significantly higher platelet count than controls (p = 0.0001), and the significantly increased platelet count in AS patients was confirmed in a meta-analysis of 14 studies involving 1,223 AS patients and 913 controls (mean difference = 39.61, 95% CI 27.89-51.34, p < 0.001). Besides, platelet count was significantly correlated with ESR (p < 0.001) and was moderately correlated with ASDAS-CRP score (p = 0.002). Moreover, anti-TNF-α therapy could reduce platelet count in AS patients at the first month and the effect was maintained through the treatment duration. In the prospective follow-up study of those 35 AS patients, those responders to anti-TNF-α therapy had significantly lower platelet count than nonresponders (p = 0.015). Logistic regression analysis suggested that lower platelet count was associated with higher possibility of achieving good response to anti-TNF-α therapy in AS patients (odds ratio = 2.26; 95% CI = 1.06-4.82; p = 0.035). Conclusion: This study suggested that platelet count was associated with inflammation severity and treatment outcomes in AS patients, and elevated platelet count was a promising biomarker of poorer response to anti-TNF-α therapy. The findings above need to be validated in more future studies.

Keywords: ankylosing spondylitis; anti-TNF-α therapy; biomarkers; platelet count; treatment outcomes.

FIGURE 1

Meta-analysis of 14 studies confirmed the significantly increased platelet count in AS patients. (WMD, weighted mean difference; 95% CI, 95% confidence interval. Black circle represents the WMD for each study, and the solid horizontal line across the square represents 95% CI for each study. The size of the gray box represents the weight for each study, and it is proportional to the sample size of each study. The diamond represents the pooled WMD, and its left and right vertices represent the 95% CI.)

FIGURE 2

Correlations of platelet count with disease activity markers in AS patients. (Platelet count had a moderate correlation with CRP (A) and ASDAS-CRP score (C) and had a significant correlation with ESR (B), but it was not correlated with BASDAI score (D).)

FIGURE 3

Forest plot in the meta-analysis of the correlations between platelet count and disease activity markers in AS patients. (Meta-analysis suggested that platelet count was positively associated with ESR but not BASDAI score or CRP (A), and AS patients with high disease activity (BASDAI ≥ 4) had significantly higher platelet count than those with low disease activity (BASDAI < 4) (B). WMD, weighted mean difference; 95% CI, 95% confidence interval. Coefficient represents the correlation coefficient between platelet count and disease activity parameters. The diamond represents the pooled correlation coefficient, and its left and right vertices represent the 95% CI.)

FIGURE 4

Impact of anti-TNF-α therapy on platelet count in AS patients. (Anti-TNF-α therapy could reduce platelet count in AS patients at the first month and the effect was maintained through the treatment duration (A). Meta-analysis confirmed the significantly reduced platelet count in AS patients after anti-TNF-α therapy (B). WMD, weighted mean difference; 95% CI, 95% confidence interval.)

FIGURE 5

AS patients with good response to anti-TNF-α therapy had lower platelet count. (Responders to anti-TNF-α therapy had significantly lower platelet count at baseline and at 3 months after treatment (^* p < 0.05).)