hirayama disease , a rare neurological disease , is characterized by insidious unilateral or bilateral muscular atrophy and weakness of the forearms and hands , without sensory or pyramidal signs .
the disease progresses initially , but spontaneous arrest is known to follow several years after the onset , unlike motor neuron disease with which it is commonly confused .
hirayama disease is characterized by focal ischemic changes in the anterior horn cells of the lower cervical cord that result in amyotrophy , which is usually unilateral but may also be bilateral .
we describe the characteristic findings of flexion magnetic resonance imaging ( mri ) suggestive of hirayama disease .
a 17-year - old male reported in the medicine out patient clinic with a one year history of slowly progressive weakness and atrophy that started in the left hand and the forearm and gradually involved the right hand .
the hand weakness limited several activities of his daily living and he could no longer play cricket because of the same .
his past medical history was noncontributory ; he denied any allergic disease and none of his family members had similar symptoms .
neurological examination revealed severely wasted and weak forearms and hands , tremors but no evidence of pyramidal , spinothalmic , posterior column lesions , polyminimyoclonus or autonomic disturbances .
plain cervical spine radiographs showed no abnormalities , or misalignment of the vertebral bodies [ figure 1 ] .
plain cervical spine ( lateral view ) radiograph shows no abnormality and no misalignment of the vertebral bodies mri was performed on magnetom concerto 2002b siemens 0.2 tesla mr unit .
the following mr sequences were used : 
 1)precontrast axial , sagittal and coronal t1 and t2-weighted spin - echo.2)post gadolinium contrast axial and sagittal t1-weighted spin - echo.3)axial and sagittal gradient - refocused echo ( gre ) flexion cervical mr study . 
 
cervical mr images in the neutral position showed focal atrophy of the lower cervical cord at the c4 - 7 vertebral levels but no abnormal intramedullary high signal intensity [ figure 2 ] . when the neck was flexed , the posterior wall of the cervical dural sac between c4 and d1 vertebral levels was seen to shift anteriorly ; the markedly flattened and anteriorly displaced cervical cord was compressed over the posterior surface of the c4 to d1 vertebral bodies .
an enhancing epidural space , isointense with the cord on t1-weighted images and hyperintense on t2-weighted images was noted at the posterior aspect of the lower cervical canal [ figures 3 and 4 ] .
cervical t1w - sagittal mr image in the neutral position shows focal atrophy of the lower cervical cord at the c4 - 7 vertebral levels but no abnormal intramedullary high signal intensity cervical gre - sagittal mr image in the flexion position shows the posterior wall of the dural sac between c4 and d1 vertebral levels to shift anteriorly , and the anteriorly displaced cervical cord compressed over the posterior surface of the vertebral bodies cervical gre - axial mr image in the flexion position shows the markedly flattened , anteriorly displaced cervical cord due to the epidural lesion ( black arrow ) the patient was prescribed a cervical collar to prevent neck flexion .
this disease was described first by , and named after , hirayama in 1959 and most cases of this disease have been reported from japan and india .
this non - familial disorder mostly hits young men , progresses slowly and is often self - limited .
researchers argue that wasting and weakness associated with this disease is because of imbalanced growth between the patient 's vertebral column and spinal canal contents .
the imbalanced growth causes a tight dural sac and displaces posterior dural wall anteriorly when the neck is flexed .
normally , the spinal dura mater is loosely anchored to the vertebral canal by the nerve roots and the periosteum at ( a ) the foramen magnum and the dorsal surfaces of c2 and c3 and ( b ) the other at the coccyx .
the dura mater is slack enough to adjust to the increased length of cervical spine in flexion . in patients with hirayama disease
, however , the tight dural sac separates the posterior dural sac from its subjacent lamina and on neck flexion , can not compensate for the increased length of the posterior wall .
the posterior dural wall shifts anteriorly , and the cervical spinal cord gets compressed against the posterior margin of adjacent vertebral bodies .
this compression affects the anterior spinal artery and causes microcirculatory disturbances in its territory in the lower cervical cord ; the anterior horn cells which are vulnerable to ischemia begin to degenerate , resulting in localized cord atrophy of the lower cervical region , weak and wasted hands and forearms . hirayama disease is also associated with raised levels of serum ige and several allergic disorders .
blood often stagnates in the compressed lower cervical cord allowing platelets to aggregate and cause histamine to be released , factors that cause arterial spasm and microcirculatory disturbances .
moreover , the finding that atopic disorders affect young people more than the elderly , men more than women , and asians more than non - asians may in part explain the distribution of hirayama disease .
the key to diagnose this disease during mri scanning is to obtain images when the neck is flexed .
mr studies in flexion not only show the anterior displacement of the posterior wall but also a well - enhanced crescent - shaped lesion in the posterior epidural space of the lower cervical canal .
although hirayama disease is a self - limiting disorder , early diagnosis is necessary because a cervical collar , by preventing neck flexion , may arrest the progression of the disorder . in conclusion
, this case showcases how cervical mri , with neck flexed , can pick up dynamic cord compression and contribute to the diagnosis of hirayama disease
 a 17-year - old male , who gave up his favorite sport cricket and started playing football , presented with one - year history of slowly progressive atrophic weakness of forearms and hands . neurological examination showed weak and wasted arms , forearms and hand but no evidence of pyramidal tract , spinothalmic tract and posterior column lesions . 
 plain cervical spine radiographs showed no abnormal findings . 
 cervical magnetic resonance imaging ( mri ) showed asymmetric cord atrophy ; images obtained with neck flexed showed the anterior shifting of the posterior wall of the lower cervical dural sac resulting in cord compression . 
 these findings suggest hirayama disease , a kind of cervical myelopathy related to the flexion movements of the neck . 
Introduction
Case Report
Discussion