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|Year : 2011 | Volume
| Issue : 1 | Page : 48-50
Hirayama's disease: The importance of flexion magnetic resonance imaging
S Jakhere, V Wagh
Department of Radiology, B.Y. L. Nair Charitable Hospital, Mumbai Central, Mumbai, Maharashtra, India
|Date of Submission||16-Mar-2010|
|Date of Decision||08-Jun-2010|
|Date of Acceptance||13-Jun-2010|
|Date of Web Publication||31-Jan-2011|
Department of Radiology, B.Y. L. Nair Charitable Hospital, Mumbai Central, Mumbai, Maharashtra
Hirayama's disease is a form of juvenile muscular atrophy affecting young individulas in their second to third decade. The underlying pathogenetic mechanism is believed to be an imbalanced growth between the individuals' vertebral column and the spinal canal contents, which causes abutment of the anterior spinal cord against the vertebral column and detachment of the posterior dura, leading to microcirculatory disturbances and ischemic changes in the cord. This mechanism is exiquisitely demonstrated on magnetic resonance imaging (MRI), but requires additional imaging, with the neck in the flexed position. Neurphysiological imaging studies have provided supporting evidence by demonstrating changes in the N13 potential, with neck flexion. Nonetheless, few studies have also reported contradictory findings with MRI and somatosensory evoked potentials, in Hirayamas Disease. This condition is underdiagnosed because most clinicians are not familiar with this disorder and do not request a flexion MRI. Early recognition of this entity and differentiation from other causes of focal cord atrophy is important, because limitation of neck flexion by using a simple neck collar can prevent its further progression. We report the classical MRI findings in a young patient with Hirayama's disease with neutral and flexion MRI.
Keywords: Hirayama′s disease, flexion cervical myelopathy, magnetic resonance imaging
|How to cite this article:|
Jakhere S, Wagh V. Hirayama's disease: The importance of flexion magnetic resonance imaging. J Postgrad Med 2011;57:48-50
| :: Introduction|| |
A 19-year-old male presented with complaints of progressive weakness in the distal muscles of both the upper limbs (right more than left) for the last seven months beginning with weakness in the fingers of the right hand. His past and family history was non-contributory. On examination, his mental status was normal and there was no cranial nerve involvement. He had severe weakness and atrophy of the distal muscles, innervated by the C7 through T1 spinal segments, predominantly on the right side, and mild weakness and atrophy of the proximal muscles innervated by C5 and C6 bilaterally in the upper limbs. The triceps reflex was lost on both the sides. A clinical diagnosis of amyotrophic lateral sclerosis was made. The MRI showed a focal atrophy of the spinal cord at the C5-C7 levels without any intra-medullary signal abnormality [Figure 1]. No extrinsic compressive lesion was seen. Considering the possibility of Hirayama's disease, an MRI was repeated after a few days, with the neck in a flexed position. The repeat MRI showed that the lower cervical cord was abutting the posterior border of the lower cervical vertebral bodies [Figure 2]. Moreover, there was detachment of the posterior dura from the vertebral bodies and was displaced forward [Figure 3]. Post gadolinium images showed intense enhancement posterior to the detached dura due to enhancement of the engorged posterior epidural venous plexus. An MRI was also done with the neck in an extended position, which showed that the posterior dura had repositioned and there was no spinal cord abutment during extension [Figure 4]. On the basis of these typical MRI findings a diagnosis of Hirayama's disease was made. It is important to make a definitive diagnosis and to differentiate it from amyotrophic lateral sclerosis, as the latter carries a poorer prognosis.
|Figure 1: Sagittal T2 weighted MRI with neck in neutral position shows focal lower cervical cord atrophy (arrow) without any intramedullary signal abnormality. No extrinsic compressive lesion is seen|
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|Figure 2: Sagittal T2 weighted MRI with neck in flexion shows abutment of the lower cervical cord against the vertebral body (thick single arrow). The posterior dura is detached and displaced forwards (thin double arrows)|
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|Figure 3: Sagittal fat saturated post gadolinium T1 weighted image shows intense enhancement of the posterior epidural venous plexus (arrow)|
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|Figure 4: Sagittal T2 weighted image in extension shows repositioning of the detached dura (double arrows)|
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Since its first description in 1959 by Hirayama et al.  several cases have been reported, mainly from the Asian countries. The initial symptoms are hand weakness and fatigue followed by cold paresis, tremors and atrophy. These symptoms progress slowly. The right upper limb is more frequently involved in Hirayamas disease regardless of the handedness. Asymmetric distribution of symptoms and signs is characteristic, although a bilaterally symmetric form has also been reported recently. 
The most widely accepted hypothesis is based on the assumption of imbalanced growth between the individuals' vertebral column and spinal canal contents. The differential growth rates between male and female patients might explain the male preponderance of the disease. Normally, the exiting nerve roots along with the dural sheath act as an anchor, to hold the dural sac in place, inside the vertebral canal. In addition the spinal dura mater is attached to the vertebral bodies at two places: one at the foramen magnum and dorsal surface of C2 - C3 and the other at the coccyx. The remaining dura mater is loosely suspended like a sac inside the vertebral column enclosed by epidural fat, venous plexus, and loose connective tissue. In the neutral position of the neck, the dura mater is slack, but with neck flexion there is an increase in the overall length of the vertebral canal. This, in turn, causes stretching of the loosely suspended dural sac, which still remains abutting the walls of the spinal canal. In patients with Hirayama's disease, because of the differential growth rate between the vertebral canal and the dura, the dural sac is shorter in length and already tighter in the neutral position. With neck flexion this tight dura then detaches from its posterior anchor and falls forward, consequently causing abutment of the spinal cord against the anterior vertebral column. The compression causes microcirculatory changes in the territory of the anterior spinal artery (usually C4 - C6 levels). These chronic circulatory changes lead to severe ischemic changes and gliosis at the site of the abutment. 
MRI depicts this pathogenetic mechanism very well because of the excellent soft tissue contrast, multiplanar capability, and lesser artefacts from the adjacent bony structures. Imaging in the sagittal plane is ideal with T1 and T2 weighted images. The MRI must be obtained in the neutral position as well as with full neck flexion. Partial flexion of the neck due to concerns about patient discomfort may not show the classical findings. A neck support should be provided to eliminate motion artefacts due to prolonged neck flexion. Neutral position MRI may reveal only focal cord atrophy in the lower cervical cord, with or without intramedullary signal abnormalities. A flexion MRI reveals the classic findings of a posterior dural detachment, with abutment of the spinal cord against the vertebral column. Postgadolinium images demonstrate intense enhancement in the engorged epidural venous plexus.
Although this is the most accepted theory for the pathogenesis of Hirayamas disease, some authors have found contradictory findings. Schroder et al.  found no significant differences in the degree of cord flattening between patients with Hirayama's disease and healthy volunteers. In contrast to previous studies, no complete obliteration of the posterior subarachnoid space was seen in any of their patients.They concluded that a compression of lower cervical cord segments and an increase in epidural space on neck flexion was seen in patients with Hirayama's disease as well as in normal individuals. Similar contradictory findings were also reported by Willeit et al. in three patients with classical clinical features of Hirayama's Disease, but no dynamic cord compression on MRI.
Neurophysiological studies such as somatosensory evoked potentials (SEP) have also contributed significantly to the understanding of the etiopathogenesis of this entity. Nalini A et al. observed that the most frequent abnormality was the absence or amplitude reduction of the cervical N13 potential, which was evident in all patients with Hirayama's disease. They concluded that reduction of the N13 potential with neck flexion, in patients with Hirayama's disease, supported the hypothesis that neck flexion could play a dominant role in explaining its pathophysiology. Their findings were in concordance with a study by Restuccia et al. published earlier. Nonetheless contradictory findings have been reported by Ammendola, et al. who observed that F wave, SEP, and MEP (motor evoked potentials) findings did not show statistically significant differences in standard conditions during neck flexion, both in HD patients and controls. It would be interesting to note that the study group evaluated by Nalini et al. had 17 patients with Hirayama's disease, whereas, the one evaluated by Ammendola et al. had only three patients.
Hirayama's disease has a self-remitting course over a few years and therefore the treatment involves reducing repeated trauma to the cervical cord by use of a cervical collar.  Early recognition of this disease is necessary because limitation of neck flexion can prevent further progression of this disease. However, a high index of suspicion and general awareness of this entity is a must to diagnose this condition, as a neutral position MRI may fail to demonstrate the classical findings.
| :: References|| |
|1.||Hirayama K, Toyokura Y, Tsubaki T, Okinaka S. Juvenile muscular atrophy of unilateral upper extremity: a new clinical entity. Psychiatr Neurol Jpn 1959;61:2190-8. |
|2.||Pradhan S. Bilaterally symmetric form of Hirayama disease. Neurology 2009;72:2083-9. |
|3.||Chen CJ, Hsu HL, Tseng YC, Lyu RK, Chen CM, Huang YC, et al. Hirayama flexion myelopathy: Neutral-position MR imaging findings-importance of loss of attachment. Radiology 2004;231:39-44. |
|4.||Schröder R, Keller E, Flacke S, Schmidt S, Pohl C, Klockgether T, et al. MRI findings in Hirayama's disease: flexion-induced cervical myelopathy or intrinsic motor neuron disease? J Neurol 1999;246:1069-74. |
|5.||Willeit J, Kiechl S, Kiechl-Kohlendorfer U, Golaszewski S, Peer S, Poewe W. Juvenile asymmetric segmental spinal muscular atrophy (Hirayama's disease): three cases without evidence of "flexion myelopathy". Acta Neurol Scand 2001;104:320-2. |
|6.||Nalini A, Praveen-Kumar S, Ebenezer B, Ravishankar S, Subbakrishna DK. Multichannel somato sensory evoked potential study demonstrated abnormalities in cervical cord function in brachial monomelic amyotrophy. Neurol India 2008;56:368-73. |
|7.||Restuccia D, Rubino M, Valeriani M, Mirabella M, Sabatelli M, Tonali P. Cervical cord dysfunction during neck flexion in Hirayama's disease. Neurology 2003;60:1980-3. |
|8.||Ammendola A, Gallo A, Iannaccone T, Tedeschi G. Hirayama disease: three cases assessed by F wave, somatosensory and motor evoked potentials and magnetic resonance imaging not supporting flexion myelopathy. Neurol Sci 2008;29:303-11. |
|9.||Tokumaru Y, Hirayama K. Cervical collar therapy for juvenile muscular atrophy of distal upper extremity (Hirayama disease): results from 38 cases. Rinsho Shinkeigaku (Clin Neurol) 2001;41:173-8. |
[Figure 2], [Figure 3], [Figure 4]
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