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Hirayama’s Disease: Myelographic, Computed Tomographic and Magnetic Resonance Imaging Findings 2003

Patel, SC
Henry Ford Hospital
Detroit, MI

Purpose:
Hirayama ’s disease, a rare form of juvenile muscular atrophy of the distal upper extremity, is increasingly being recognized in America after first reported in Japan. Dynamic imaging of cervical spine in extension and flexion position with magnetic resonance imaging, post myelogram computed tomography of the cervical spine and myelography can accurately diagnose Hirayama’s disease in young males who present in the second or early third decade with a muscular weakness and atrophy in the hand and forearm. Static magnetic resonance imaging may reveal focal atrophy of the cervical spinal cord.

Methods & Materials:
15-year-old male presented with progressive painless weakness and wasting of the right hand muscles begin at 13 years of age. Clinical diagnosis of benign focal amyotrophy was suggested. Clinical differential diagnosis included multi-focal motor neuropathy with conduction block and monomelic amyotrophy. Magnetic resonance imaging showed a focus of bright signal on T2W images within the atrophic spinal cord. Based on clinical and MRI findings, repeat magnetic imaging study was performed with flexion and extension views in sagittal plane using T1W and T2W images. Subsequently, contrast myelography was performed with the lateral projection of the cervical spine obtained in flexion, neutral and extension position. Post myelogram computed tomography of cervical spine were also obtained in flexion, extension and neutral position. Focal atrophy of the spinal cord was demonstrated on myelogram, computed tomography and MRI. However, there was forward migration of the posterior surface of the dura with subsequent compression of the cervical spinal cord in flexion position, which was maximum at the area of focal atrophy of the cervical spinal cord at C6-C7.

Conclusion:
Finding of forward migration of the posterior surface of the dura with compression of the cervical spinal cord in flexion position seen on myelography, post myelogram computed tomography and magnetic resonance imaging done in flexion position can confidently suggest in the appropriate clinical setting, the diagnosis of Hirayama’s disease, which is also known as monomelic amyotrophy, benign focal amyotrophy, juvenile muscular atrophy of a unilateral upper extremity and juvenile asymmetric segmental muscular atrophy. The clinical course is slow and progressive and becomes stable by 30 years of age after initial progression of disease. Hirayama suggested that the continuous dynamic compression of the cervical spinal cord in flexion by a forward displaced posterior dura is of pathological significance. Kikuchi suggested that “tight” dural canal in flexed position is due to disproportional length between vertebral column and dural canal. Hard cervical collar, duraplasty or surgical fusion may help some of these patients. Early recognition of this condition by imaging is essential as avoidance of neck flexion can prevent progression of disease as a stable neurological status may be reached within 3 to 4 years.