Styloid Process Elongation on Cervical Spine Computed Tomography is Associated with the Enthesopathy-Related Diseases of Ankylosing Spondylitis and Diffuse Idiopathic Skeletal Hyperostosis.

Background: Enthesopathy may lead to calcification of the stylohyoid ligament and can cause elongation of the styloid process (SP).

Objectives: To evaluate whether SP elongation is associated with two common enthesitis-related diseases: ankylosing spondylitis (AS) and diffuse idiopathic skeletal hyperostosis (DISH).

Methods: Cervical spine computed tomography (CT) examinations of patients with DISH (n=64, Resnick criteria), AS (n=24, New York criteria) and a controls (no radiological signs of DISH or AS, n=54) were retrospectively evaluated. The DISH group was further divided into patients with and without cervical DISH. The length of right and left SP was measured independently by two readers on coronal and sagittal curved reformats. The average right and left styloid length and average length per person were compared among the groups.

Results: Demographic characteristics were similar between the DISH and control groups (average age 68.2 ± 15.7, 69.2 ± 12.7 years, male:female ratio 48:16 and 35:19, respectively, P > 0.05), whereas age was significantly lower (average age: 53 ± 15 years, P < 0.0001) in the AS group, which was also composed mainly of men. The AS and DISH groups had significantly longer SP compared to controls (AS 37.9 ± 9.6 mm, DISH 34.4 ± 9 mm, control 30.3 ± 10.1 mm, P < 0.05). There was no correlation between age and SP length. Inter-reader reliability of SP measurements was excellent in all groups (ICC = 0.998, P < 0.0001).

Conclusions: SP elongation is associated with both AS and DISH substantiating the enthesopathy-related pathophysiology of this finding.