Diffuse idiopathic skeletal hyperostosis: A potential factor in the induction of thoracic spondylotic myelopathy

Thoracic spondylotic myelopathy (TSM) commonly occurs at the thoracolumbar junction, and mechanical stress is thought to be involved. In DISH, the anterior longitudinal ligament becomes ossified. Although DISH is suspected to be involved in TSM pathology, reports are limited. Aim of this study is to investigate the association between (TSM) and diffuse idiopathic skeletal hyperostosis (DISH).

Fifty-one patients with thoracic myelopathy underwent surgery between April 2008 and April 2017. Of these, 28 patients with TSM were included and examined. DISH was confirmed using computed tomography (CT). Subjects were divided into DISH and non-DISH sub-groups according to CT findings, and the DISH coexistence rate was calculated. Groups were analyzed for sex, age, postoperative Japanese Orthopedic Association (JOA) score, and reoperation status. In the DISH group, the positional relationship between the affected vertebral level of TSM and consecutive vertebral bone bridges was analyzed. Patients without spinal disease matched for sex and age were enrolled as controls (N = 56). The DISH coexistence rate was compared and analyzed between groups.

Mean age at surgery was 67.8 years (43-82 years; 22 men, 6 women). DISH was detected in 17 of 28 patients (60.7%; 15 men, 2 women). No significant difference in the improvement rate of JOA score was observed between groups. TSM occurred at: lower border of a consecutive vertebral bone bridge, N = 4; upper border, N = 3; between consecutive vertebral bone bridges, N = 5; one vertebral body away from a consecutive vertebral bone bridge, N = 5. No patient had TSM occurring within a consecutive vertebral bone bridge. The DISH coexistence rate in patients with TSM (60.7%) was significantly higher than that in controls (20/56, 35.7%) (p = 0.03).

Mechanical stress caused by consecutive vertebral bone bridges due to DISH may be involved in TSM pathogenesis. Therefore, in DISH patients, attention needs to be paid to TSM onset.