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Similar stiffness, different clinical questions

DISH and ankylosing spondylitis, often shortened to AS, can both produce a stiff spine with bony bridges. They are not interchangeable diagnoses. AS belongs to the inflammatory axial spondyloarthritis spectrum. DISH is characterized by prominent ossification at ligament and tendon attachments, with a different pattern and incompletely understood cause. Comparing labels is useful only when the history, examination and complete imaging are considered together.1

DISH often has broad, bulky flowing bridges along the front and side of vertebrae. AS can show thinner, more vertically oriented syndesmophytes and inflammatory sacroiliac changes. These are descriptive tendencies, not a reliable home sorting exercise. Age at presentation, symptom pattern and other clinical features help interpretation, and atypical or overlapping appearances exist.1

Sacroiliac joints are a source of nuance

The sacroiliac joints connect the sacrum to the pelvis. Classic DISH criteria excluded certain SI-joint findings, which can lead to the mistaken statement that these joints must always be normal in DISH. Later CT work has shown bridging outside the joint and other changes. Yahara's study compared 86 DISH and 85 matched non-DISH lumbar surgery patients; its selected population cannot represent everyone with DISH.2

An anterior bridge outside the joint, intra-articular fusion and erosive inflammatory changes are different observations. They require specialist interpretation in context. Neither a single SI-joint change nor its absence conclusively resolves the diagnosis for a reader. A person may need rheumatology assessment when inflammatory disease remains a concern.1

Degeneration and OPLL are also distinct

Degenerative spondylosis refers to wear-related changes involving discs and joints, often with osteophytes. DISH has a different characteristic pattern but degeneration can be present alongside it. Relative disc-height preservation is a feature of classic DISH classification, not a promise that every affected person's discs are normal.1

OPLL means ossification of the posterior longitudinal ligament. “Posterior” matters: that ligament lies behind the vertebral bodies within the spinal canal, unlike the prominent anterior bridges usually discussed in DISH. Canal narrowing or neurological symptoms require their own assessment. Chung's selected cervical dysphagia cohort included patients with coexisting ossifying conditions; coexistence does not make those conditions synonymous.3

Why the distinction changes care

A treatment studied for active inflammatory AS cannot automatically be offered as a disease-modifying treatment for DISH. Conversely, an osteophyte operation aimed at swallowing obstruction does not treat the inflammatory biology of AS or all causes of spinal pain. “Noninflammatory” is a conventional distinction from AS, not an absolute claim that local inflammation has no possible role in DISH.1

Both conditions can produce ankylosis, so injury evidence often combines them. A fracture recommendation from a mixed ankylosed-spine population must be labeled as such. The urgency of assessing a possible unstable injury is different from deciding which chronic diagnosis best fits the images.4

Useful consultation questions are: what supports each diagnosis, which conditions coexist, and which finding explains the current symptom? Ask what further assessment would change the plan. Avoid changing medication or adopting an AS treatment on the basis of an imaging comparison page.

References

  1. Mader R et al. RMD Open. 2017;3:e000472. doi:10.1136/rmdopen-2017-000472. Source ↩
  2. Yahara Y et al. BMC Musculoskeletal Disorders. 2020;21:93. doi:10.1186/s12891-020-3105-z. Source ↩
  3. Chung YS et al. Yonsei Medical Journal. 2020;61:341–348. doi:10.3349/ymj.2020.61.4.341. Source ↩
  4. Reinhold M et al. Global Spine Journal. 2018;8(2 Suppl):56S–68S. doi:10.1177/2192568217736268. Source ↩