Hirayama disease: MRI spectrum of a rare disease

3 male patients of 17, 21 and 25 years of age respectively presented with complaints of bilateral upper limb weakness, gradually increasing tremors and fasciculations in bilateral upper limbs of 2-4 months duration. Complaints were more significant in one limb than the other.

Patients underwent MRI cervical spine with additional flexion and post-contrast imaging.
Case 1: On Neutral MRI, there is mild to moderate cord flattening. On flexion MRI, there is flattening of the spinal cord, obvious posterior dural detachment and prominent venous flow voids on the T2-weighted image. Post-contrast images show mild homogenous post-contrast enhancement.
Case 2: On MRI, there is abnormal cervical curvature and focal atrophic changes at C6-7 level. There is a forward movement of cord with a reduced anteroposterior diameter on the flexion scan. There is a forward displacement of lower cervical vertebrae, flattening of the spinal cord and obvious posterior dural detachment.
Case 3: On neutral MRI, there is an abnormal cervical curvature and focal T2 hyperintense signal in the cervical cord. On flexion MRI, there is flattening of the spinal cord, loss of posterior dural attachment and prominent venous flow voids on T2-weighted image.

Hirayama disease is also known as JMADUE (juvenile muscular atrophy of distal upper extremity) or oblique amyotrophy, is a form of upper motor neuron disease affecting young adults in the age group of 20–30 years [1]. Patients present with progressive upper limb myopathy in the form of weakness and tremors [2].
The postulated aetiopathogenesis is the discordant growth of the vertebral column and spinal cord. There is at least a discrepancy of 5 cm in the change in length along the anterior and posterior surface of the cervical canal. This is compensated by the transverse dural folds [3]. However, in patients with hirayama disease, it has been postulated that there is a lack of these transverse folds resulting in dural stress.  Undue flexion of the cervical spine results in loss of posterior dural attachment. This dynamic narrowing of the spinal canal in flexion produces compression of the cord at these levels, typically seen from C7 to D1 level [1,4].
 The condition should be suspected when a young male presents with progressive peripheral weakness of arms and forearms, dystonia, tremors, fasciculation [5] with an abnormal curvature of the cervical spine.
MRI findings suspicious of the condition are focal T2-hyperintensity involving cervical cord, asymmetric flattening of cervical cord on the axial section and posterior dural detachment from the lamina. This feature of loss of attachment is often the most specific sign for the diagnosis of hirayama disease. [3, 6]
Confirmation of the diagnosis of hirayama disease can be done by performing a flexion/ extension MRI. On flexion, there is stretching of the posterior dura, anterior dural shift, and compression of the spinal cord at the site corresponding to the abnormal hyperintense signal. The resulting dural shift may vary from patient to patient ranging from 0 mm to 7 mm [6]. There are prominent venous flow voids on the flexion scan.
Dural detachment may be seen only early in the course of the disease in young patients or in the progressive form, and this finding becomes less prominent with advanced age and chronic stages of the disease.. Post-contrast MRI acquired in flexion position often reveals crescent-shaped enhancement of posterior epidural space on fat-suppressed T1-weighted images, which is hypointense on T1WI and hyperintense on T2 weighted images [7].
EMG/nerve conduction-study may be ordered to confirm the clinical and imaging diagnosis [8].
Hirayama disease is a self-limiting condition, so conservative stabilisation of neck with cervical collar prevents further progression of the disease [9].
Written informed patient consent for publication has been obtained.