Cervical flexion myelopathy in a patient showing apparent long tract signs: a severe form of Hirayama disease.

We describe an 18-year-old male with cervical flexion myelopathy with Hirayama disease-like features who showed apparent long tract signs. He first experienced insidious-onset hand muscle weakness and atrophy at the age of 15. Subsequently, he developed sensory disturbance in his lower limb. Neurological examination revealed atrophy and weakness in the right hand and forearm, pyramidal signs in the right lower extremity, and disturbance of superficial sensation in the lower left half of the body. Cervical magnetic resonance images and computed tomographic myelography revealed anterior displacement with compression of the cervical cord in flexion that was more apparent in the right side. The right side of the cervical cord showed severe atrophy. The mechanisms of myelopathy in our patient appeared to be same as that of "tight dural canal in flexion," which has been reported to be the mechanism of juvenile muscular atrophy of the unilateral upper extremity (Hirayama disease). Patients with Hirayama disease generally show minimal sensory signs and no pyramidal signs. An autopsy case of Hirayama disease revealed confined necrosis of the cervical anterior horn without obvious changes in the white matter. Our patient's disease progression suggests that cervical flexion myelopathy patients with severe cervical cord compression in flexion may develop extensive cervical cord injury beyond the anterior horn.