Which condition is defined by ossification of the longitudinal ligaments of the spine producing syndesmophytes?

• A. Diffuse idiopathic skeletal hyperostosis (DISH)
• B. Ankylosing spondylitis
• C. Ossification of the posterior longitudinal ligament
• D. Gout

Answer: (A)

Ossification of the spinal longitudinal ligaments forming bridging across vertebrae is the hallmark of this condition, with the anterior longitudinal ligament most prominently involved. In diffuse idiopathic skeletal hyperostosis, you see flowing calcifications that extend across four or more adjacent vertebral levels, creating syndesmophyte-like bridges while the intervertebral disc spaces are typically preserved and the sacroiliac joints are not inflamed. This pattern helps distinguish it from other causes of spinal syndesmophytes.

If you compare it with other possibilities, ankylosing spondylitis also forms syndesmophytes, but it is driven by inflammatory back pain, HLA-B27 association, and sacroiliitis, leading to a bamboo spine from inflammatory changes rather than the characteristic flowing anterior ligament ossification seen in DISH. Ossification of the posterior longitudinal ligament occurs on the back of the spinal canal and can cause myelopathy, not the anterior-flowing bridging across multiple levels. Gout involves urate crystal deposition with joint inflammation, not ligament ossification and vertebral bridging.