Cervical Spine Deformity as a Cause of Hirayama Disease (P4.095)

Objective: The aim of this study is to assess cervical spine deformities in Hirayama disease(HD). Background: HD is a cervical segmental myelopathy characterized by juvenile onset of muscular atrophy in unilateral upper extremities. In HD, cervical cord is compressed by expanding the posterior extradural space and forward displacement of the spinal cord at C6 vertebral level at neck flexion position. These findings suggest a circulatory insufficiency of the lower cervical cord, resulting in ischemic necrotic changes of the anterior horns of the cervical cord. The etiology of HD is disproportionate growth during the juvenile period between the vertebral column and the contents of the spinal canal, additionally; cervical spine deformity may be frequent comorbidities in HD. Methods: We enrolled 14 patients with HD (all male, mean age: 20.6±5.6 years) and 108 normal subjects younger than 30 years, who underwent cervical spine MRI between January 2010 and August 2015. We evaluated cervical spine sagittal alignment at neck neutral position by using the following methods: [circ1] C2-7 Cobb, [circ2] Centroid measurement of cervical lordosis (CCL), [circ3] absolute rotation angle (ARA), [circ4] C7 slope (C7S), [circ5] Ishihara curvature index (ICI) according to previously established methods. Result: The angle using C2-7 Cobb, CCL and ARA in HD significantly reduced compared with controls (mean C2-7 Cobb: -5.98 versus 3.15; p=0.009, mean CCL: -6.24 versus 6.62; p<0.001, mean ARA: -5.24 versus 8.51; p<0.001). Additionally, ICI in HD was smaller than controls (-2.56 versus 6.98; p<0.001). No significant differences between groups were found for C7S (5.37 versus 33.1; p=0.594). Conclusion: These findings indicate that straight neck or even lordosis is frequently seen in patients with HD compared with controls. These abnormal alignments of the cervical spine may partially contribute the pathogenesis of the HD. Disclosure: Dr. Yokote has nothing to disclose. Dr. Tsugawa has nothing to disclose. Dr. Ouma has nothing to disclose. Dr. Tsuboi has nothing to disclose.