Radiologic Features Compared Between Diffuse Idiopathic Skeletal Hyperostosis and AS

Radiologic features were compared between among patients with diffuse idiopathic skeletal hyperostosis (DISH) and those with ankylosing spondylitis (AS), in a study published in Scientific Reports.

DISH is typically characterized by the presence of calcification and ossification of the anterior vertebral body, along with peripheral entheses, which causes the bony bridging of multiple vertebral bodies. The Resnick criteria is most commonly used to diagnose DISH.

On the other hand, AS is associated with severe spinal ankylosis, chronic inflammation, as well as the presence of the human leucocyte antigen (HLA) B27; AS is typically diagnosed based on the modified New York criteria.

The researchers of the study sought to assess the radiologic differences between DISH and AS, using whole-spine computed tomography (CT) of the spine and the sacroiliac joint (SIJ).

A total of 138 patients were enrolled in the study — 111 in the DISH group (83 men; mean age, 68.0±11.8 years) and 27 in the AS group (21 men; mean age, 47.0±12.5 years).

Results of the study showed that complete SIJ fusion was statistically significantly higher in participants with AS compared with those with DISH (P <.001). With regard to SIJ, 63% of patients with DISH had a partial or complete fusion, whereas no evidence of SIJ fusion was observed in19% of patients with AS. In addition, anterior bony bridging and posterior bridging were both significantly higher among participants with DISH compared with those with AS (P <.001 and P =.025, respectively).

Following age- and sex-matching, SIJ fusion continued to be significantly higher among patients with AS than those with DISH; anterior bony bridging continued to be significantly higher among patients with DISH than those with AS (P <.001 for both).

Anterior bony bridging was statistically significantly higher in the lumbar region among participants with AS compared with those with DISH (P =.009). In addition, the percentage of candlewax-type bone bridging was significantly higher in patients with DISH than those with AS (P <.001). A total of 11% of patients with DISH had 0% to 30% of candlewax bridging, and up to 21% of patients with AS had 30% to 70% of candlewax bridging.

In terms of spinal facet fusion, 83% of patients with AS compared with 61% of those with DISH showed facet fusion. The number of facet fusions on both sides of the spine was significantly higher among participants with AS than those with DISH in T1 to T6 (P =.004), T7 to T12 (P <.001), the lumbar spine (P <.001), and the whole spine (P <.001). In contrast, the number of no-facet fusions was significantly higher among patients with DISH compared with those with AS in T1 to T6 (P =.002), T7 to T12 (P <.001), the lumbar spine (P <.001), and the whole spine (P <.001).

Study limitations included the small sample size, the dependency of number of bony bridges and fusions on patients’ age, and the lack of considering the possibility of the co-occurrence of AS and DISH in the same individual.

“In conclusion, both sides of complete SIJ fusion are common in patients with AS, and anterior/posterior bridging around the SIJ is common in patients with DISH,” the researchers noted. “These results are useful in differentiating DISH from AS and should therefore be considered when making a diagnosis,” they concluded.