In-Depth Understanding of Hirayama Disease: Dural Detachment Beyond Cervical Spine.

Background and objectives: Hirayama disease (HD) is a cervical flexion-induced compressive myelopathy. Typically, there is forward displacement and loss of attachment of dural sac to lamina at the cervical level during neck flexion. However, the extent of the dural detachment (DD) has not been studied carefully. We undertook this study to know the extent of DD in HD.

Methods: We conducted a retrospective study of HD patients evaluated from 2015 to 2023. Patients with DD extending beyond the cervical spine were selected, and their clinical and radiological features were studied.

Results: One hundred and thirty-two (62.8%) patients were identified to have DD beyond the cervical spine in a cohort of 210 HD patients. The mean age at onset and duration were 18.09 ± 2.3 years (13-26) and 38.63 ± 39.9 months, respectively. Proximo-distal involvement was noted in 50% of patients, while 33% and 17% of patients had isolated distal and proximal involvement, respectively. Wasted legs were observed in three patients. Cord atrophy was present in 96.9% of patients, extending from C5 to C7. Epidural detachment and engorgement of posterior epidural venous plexus were evident in all. DD extended from C2 to D10 vertebral level. The cranial extent of DD was from C2 to C4 in 87% of cases, and the caudal extent was D1-D5 in 84% of cases, extending up to D10 in two cases.

Conclusions: The HD spectrum continues to evolve phenotypically and radiologically. The pathophysiological mechanisms and DD extend beyond the cervical spine in a large proportion of patients. This makes it important to cover a longer part of the spine during imaging. This may have implications on the management of patients, particularly those with isolated lower limb involvement.