BackgroundThis study aimed to assess the efficacy of water-filtered infrared A (wIRA) in sacroiliitis in male patients with ankylosing spondylitis (AS) and the effect of wIRA therapy on serum vascular endothelial growth factor (VEGF).MethodsOne hundred twenty male AS patients with active sacroiliitis were randomly divided into wIRA group and control group. wIRA treatment was performed twice daily for 5 consecutive days with 24-h interval before switching the treatment (crossover design). Bath ankylosing spondylitis disease activity index (BASDAI) scores, pain visual analogue scale (VAS), and morning stiffness VAS were recorded prior to and after each treatment period. Additionally, C-reactive protein (CRP), serum VEGF, and resistance index (RI) of sacroiliac joints detected by ultrasonography were recorded at baseline and after the first and second treatment period, respectively. The efficacy was examined by using repeated measures analysis of variance (ANOVA).ResultsBASDAI, pain VAS, and morning stiffness VAS scores decreased significantly (P < 0.001) after wIRA treatment and no-wIRA treatment (control group), and the difference between the two groups was significant (P < 0.001). CRP declined and RI increased during the wIRA treatment as compared with the no-wIRA treatment (P < 0.001). The increase in RI was associated with improvement of pain VAS scores (P = 0.018), while serum VEGF was unaffected by the treatment.ConclusionswIRA treatment achieved symptom and pain relief for AS patients with active sacroiliitis. wIRA treatment also improved RI revealed by ultrasonography, and this effect was associated with improved pain VAS scores.