Unveiling the distinctive ossification patterns of diffuse idiopathic skeletal hyperostosis and ankylosing spondylitis using computed tomography three-dimensional reconstruction

Objective: To quantitatively analyse the morphological characteristics of osteophytes in DISH and syndesmophytes in AS, and summarize different ossification patterns to help identify the two diseases. Associated factors for new bone formation would be investigated. Methods: Fifty patients with DISH and 50 age-, sex-, CT examination site-matched patients with AS were enrolled. Radiographic and clinical data were reviewed. Osteophytes (syndesmophytes) in front of each vertebral body and the corresponding intervertebral disc space were defined as vertebral osteophytes unit (VOU). The volume, angle and location (contralateral, ipsilateral, bilateral) of osteophytes in each VOU were measured and compared between DISH and AS groups. Results: In each VOU, the volume and angle of osteophytes in DISH were significantly larger. The best osteophytes volume and angle cutoff value in predicting DISH was 0.59 cm(3) and 40.15 degrees. Contralateral, bilateral, ipsilateral osteophytes were recorded in 59.32%, 36.38%, 4.3% of assessed VOUs in patients with DISH and 64.78%, 29.31%, 5.91% in AS (P <0.001), respectively. As to ipsilateral osteophytes, the volume was inversely correlated with the centre of the vertebral body to the centre of the descending aorta (DISH: r=-0.45, P =0.01; AS: r=-0.83, P <0.001). Advanced age, disease duration, smoking and overweight contribute to the progression of osteophytes and syndesmophytes. Conclusion: Morphological features of osteophytes are helpful to distinguish DISH with AS. Aortic pulsations inhibit or hinder new bone formation in both DISH and AS. Maintaining normal BMI could postpone osteophytes formation.