A 40-year-old male with a 3-year history of low back pain with short duration morning stiffness. Treatment with nonsteroidal anti-inflammatory drugs showed partial improvement. B27 is negative and C-reactive protein is 20 mg/L. Pelvic radiograph demonstrates suspicious changes of the right sacroiliac joint (SIJ) and minimal abnormalities of the left SIJ, not fulfilling the 1984 modified New York criteria for the diagnosis of ankylosing spondylitis.