Efficacy of Non-invasive Vagus Nerve Stimulation for Axial Spondyloarthritis Resistant to Biotherapies

The primary objective of the study is to study the change in SpA disease activity, according to ASAS20 definition (Anderson et al., 2001), after 8 weeks of VNS treatment versus placebo non-specific stimulation (control group). The secondary objectives of the Clinical Investigation are to show differences in disease evolution between the active and placebo periods of 8 weeks treatment with active VNS versus placebo VNS of the following items: 1. Change in disease activity according to \"ASAS40\" criteria 2. Obtaining a partial remission according to the ASAS definition 3. Change in BASFI 4. Change in C-reactive protein (CRP)serum level and erythrocytes sedimentation rate (ESR), 5. Change in ASDAS_CRP and ASDAS_ESR 6. Difference in levels of circulating cytokines, IL-6, IL-23, IL-17, IL-33 and of matrix metallopeptidases (MMP3-8-9). 7. Change in quality of life : assessment according to the following indexes: SF-36, AS Quality of Life (ASQOL) 8. Change in Health Index of patient with SpA (ASAS HI) and of the Productivity at Work Index (WPI) 9. Change in fatigue (BASDAI 1st question) and global pain 10. Change in Anxiety and Depression Assessment (HAD) 11. Change in BASMI 12. Change in non-steroidal anti-inflammatory drugs (NSAID) intake score.