An 18 yo male with 4 year history of slowly progressive weakness of forearms and hand marked on right side. Neurologic examination revealed atrophic changes in thenar, hypothenar muscles, interossei of the hands, muscles of forearm more on right side. Deep tendon reflexes symmetrically normal. No Babinski sign. Normal pin-prick, vibration and joint position sensation. No extra pyramidal signs.
Previous MRI cervical spine report at other center mentions spinal cord atrophy in lower cervical region. Rest of the spine and spinal cord screening unremarkable.
We performed MRI Cervical spine, sagittal T2w MR images revealed cord atrophy at the C5-6 disc level, a linear signal abnormality in anterior half of cord. The atrophy marked in anterior half of cord, signal abnormality confined to anterior half of cord in the region of either side anterior horn cells marked on right side confirmed on Axial T2w images. Study repeated during flexion with clinical suspicion of Hirayama disease shows marked anterior displacement of the posterior wall of dura with marked flattening of the cord. Flow void noted in this posterior epidural space appears to be the engorged venous plexus due to dural shifting. Clinical presentation and flexion MR imaging findings led to the diagnosis of Hirayama disease. Neck collar was advised to prevent neck flexion and to prevent further progression of disease and disease symptoms with follow up MRI Imaging.
Hirayama et al first reported this disease in 1959.
Hirayama disease, a non progressive juvenile spinal muscular atrophy, occurs mainly in young males between the ages of 15 and 25 years. The clinical features include insidious onset, predominantly unilateral upper extremity weakness and atrophy, cold paresis, and no sensory or pyramidal tract involvement.
Pathologic studies have shown the lesions only in the anterior horns of the spinal cord from C-5 to T-1, particularly marked at C-7 and C-8.
Current neuroradiologic techniques have shown forward displacement of the posterior wall of the lower cervical dural canal in neck flexion, which is presumed to be a primary
pathogenetic mechanism of Hirayama disease. The mechanism of this anteriorly displaced dural canal has been explained by Kikuchi et al as a tight dural canal in flexion,
caused by a disproportional length between the vertebrae and the dural canal.
Early diagnosis of disease is necessary, because placement of a cervical collar will prevent neck flexion, which has been shown to stop disease progression. Atrophy on routine nonflexion MR studies especially at the lower cervical cord, should raise the suspicion of Hirayama disease. When this sign is seen, a flexion MR study should be performed to confirm the diagnosis.
Reference : Hirayama Disease: MR Diagnosis, Chi-Jen Chen, Chiung-Mei Chen, Chia-Lun Wu, Long-Sun Ro, Sien-Tsong Chen, and Tsong-Hai Lee, AJNR Am J Neuroradiol 19:365–368, February 1998