Abstract
BACKGROUND: Ankylosing spondylitis (AS) is a chronic inflammatory disease characterized by high relapse. Therefore, the present study aimed to investigate the ultrasonographic features of contrast-enhanced ultrasonography (CEUS) in the sacroiliac joint (SIJ) in patients with AS in remission after discontinuation of anti-tumor necrosis factor (TNF) therapy, and also examined the role of CEUS in predicting relapse. METHODS: In this prospective observational study, 130 SIJs in 65 patients with AS (according to modified New York criteria) satisfying Ankylosing Spondylitis Disease Activity Score (ASDAS) inactive disease after discontinuation of anti-TNF therapy were investigated on color Doppler ultrasonography (CDUS) and CEUS. Vascularization and the resistive index (RI) of the SIJ were observed and measured. We defined no blood flow, high RI of arterial blood flow (RI ≥0.7), the reversed phase in the diastolic phase or venous blood flow in the bilateral SIJs, as negative CDUS/CEUS; meanwhile, low RI of arterial blood flow (RI <0.7) in the unilateral or bilateral SIJs was defined as positive CDUS/CEUS. All the patients were followed up for 52 weeks until relapse. Relapse was defined as an increase of two or more items in comparison with the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) at the time of anti-TNF withdrawal. RESULTS: After 52 weeks, 46 of the 65 patients (70.8%) had relapse. The mean time to relapse was 31.4 weeks (±8.4 weeks, range 20 to 52). After discontinuation of anti-TNF therapy, positive CEUS accounted for 61.5%; this was significantly more than positive CDUS (13.8%). The vascularization detected by CEUS for patients of relapse was significantly different from that of patients with remission (P<0.05). In addition, patients with negative CEUS had a longer duration of remission than the patients with positive CEUS (P=0.005). A Cox proportional hazards regression analysis found that the disease duration could also be regarded as a factor predictive of relapse in patients with AS. CONCLUSIONS: The use of CEUS distinctly improved the detection of vascularization in the SIJ in patients with AS in remission after anti-TNF withdrawal. The presence of vascularization in the SIJ detected by CEUS at the time of anti-TNF withdrawal could yield a valuable predictor of relapse in patients with AS. A significant limit of this study is the lack of magnetic resonance imaging (MRI) as the standard reference.