The patient, a 26-year old woman diagnosed with HLA-B27-associated ankylosing spondylitis (AS) currently not on therapy complained of new-onset mid-back pain. The pain was particularly noticeable during inspiration and yawning. Point tenderness at two costo-vertebral joints (CVJ) on both sides of the spine was noted. Electrocardiogram and chest X-ray were unremarkable. Laboratory studies showed elevated inflammatory markers. Magnetic Resonance Imaging (MRI) of the spine and sacroiliac joints (SIJ) revealed left-sided sacroiliitis.