A 23-year-old man comes to the physician because of a 3-month history of lower back pain that is worse in the morning upon waking. Stretching helps relieve the pain. He reports occasional dysuria. Physical examination shows reduced flexion of the spine and tenderness of the lumbosacral area and Achilles tendon. Which of the following is the most likely diagnosis?
Ankylosing spondylitis
Intervertebral discitis
Lumbar spinal stenosis
Spondylolisthesis
Spondylosis
