Hirayama disease, also termed non-progressive juvenile spinal muscular atrophy of the distal upper limbs, is a type of cervical myelopathy related to flexion movements of the neck. It is considered a benign motor neurone disorder with a stationary stage after a progressive course.
It typically occurs mainly in young males between the ages of 15-25 years 6.
It is often of insidious onset presenting with a predominantly unilateral upper extremity weakness and atrophy, cold paresis, and no sensory or pyramidal tract involvement. It is also characterised by muscle weakness and atrophy in the hand and forearm with sparing of the brachioradialis, giving the characteristic appearance of oblique amyotrophy that affects the C7, C8 and T1 myotomes 5,6. The amyotrophy is unilateral in most patients, asymmetrically bilateral in some and rarely symmetric 5.
Chronic microcirculatory changes in the territory of the anterior spinal artery induced by repeated or sustained flexion account for the necrosis of the anterior horns of the lower cervical cord, which is the hallmark of pathology 5.
On myelograms and flexion-extension MR images, there can be a forward migration of the posterior wall of the dura mater. The posterior epidural space becomes enlarged with flexion and is seen as a crescent of high signal intensity on T1- and T2-weighted MR images, with or without epidural flow voids. Uniform enhancement of this epidural space occurs with administration of contrast material.
At the site of maximal forward shift of the posterior dural sac the spinal cord is dynamically compressed with a reduction in the AP diameter of the cord compared to neutral imaging 6.
History and etymology
It was initially described Keizo Hirayama et al. in 1959 2.
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