Lateral radiograph of the thoracolumbar spine in a 28-year-old man with chronic low back pain shows fine, vertical bony bridges connecting adjacent vertebral bodies along their anterior and lateral aspects, plus a single central vertical dense line overlying the spinous processes. What is the most likely diagnosis?

• A Diffuse idiopathic skeletal hyperostosis
• B Ankylosing spondylitis ✓
• C Psoriatic spondyloarthropathy
• D Degenerative disc disease with osteophytes

Explanation

Thin marginal syndesmophytes bridging adjacent vertebral bodies combined with ossification of the supraspinous and interspinous ligaments, the dagger sign, are classic for advanced ankylosing spondylitis, giving the bamboo spine appearance. Diffuse idiopathic skeletal hyperostosis produces thick, flowing, coarse ossification along the anterolateral aspect spanning at least four vertebrae with preserved disc height and no facet fusion. Degenerative disease produces horizontal osteophytes, not vertical marginal syndesmophytes.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.