Hirayama Disease Radiology: A Comprehensive Review
Hirayama disease, also known as Juvenile Muscular Atrophy of the Distal Upper Extremity (JMADUE) or oblique amyotrophy, is a rare neurological disorder that primarily affects young individuals in the age group of 15-25 years, particularly in Asia [^1^]. It is characterized by progressive weakness and atrophy of the distal upper limbs, leading to significant functional impairment. In this comprehensive review, we will delve into the radiological aspects of Hirayama disease, focusing on its imaging findings and diagnostic utility.
Hirayama disease primarily affects young Asian males, with a peak incidence in the second and third decades of life [^1^]. The clinical presentation is insidious, with patients often reporting unilateral upper extremity weakness and atrophy. The affected limb may also exhibit cold paresis, with no associated sensory or pyramidal tract involvement [^1^][^2^]. Notably, the brachioradialis muscle is spared, giving rise to the characteristic appearance of oblique amyotrophy [^2^]. The weakness and atrophy predominantly affect the hand and forearm, with the involvement of the C7, C8, and T1 myotomes [^5^]. While amyotrophy is typically unilateral, it may occasionally be asymmetrically bilateral or even symmetric [^5^].
The underlying pathology of Hirayama disease involves chronic microcirculatory changes in the territory of the anterior spinal artery, induced by repeated or sustained flexion movements of the neck [^5^]. These changes lead to necrosis of the anterior horns of the lower cervical cord, which is the hallmark of the disease's pathology [^5^]. The exact mechanism behind these microcirculatory changes and subsequent necrosis is not fully understood. However, it is postulated that there is a lack of transverse dural folds in individuals with Hirayama disease, resulting in dural stress and dynamic compression of the spinal cord during flexion [^4^].
MRI plays a crucial role in the diagnosis and evaluation of Hirayama disease. It allows for the visualization of structural abnormalities and dynamic changes in the cervical spine during flexion and extension.
In the neutral position, MRI may reveal abnormal T2-weighted signal intensity of the spinal cord at the site of maximum anterior shift without an obvious cause [^5^]. Additionally, there may be subtle findings such as loss of physiological lordosis, asymmetric atrophy, and increased T2 signal intensity of the lower anterior cervical cord [^6^]. These findings, although not specific to Hirayama disease, can raise suspicion and prompt further investigation.
the MRI in the flexion position is crucial for the diagnosis of Hirayama disease, as it allows for the visualization of dynamic changes that occur during neck flexion. One of the key findings is the forward migration of the posterior wall of the dura mater, resulting in the enlargement of the posterior epidural space, which is seen as a crescent [^5^]. The spinal cord is dynamically compressed at the site of maximal forward shift of the posterior dural sac, leading to a reduction in the anteroposterior diameter of the cord compared to neutral imaging [^6^]. Furthermore, there may be stretching of the posterior dura, anterior dural shift, and compression of the spinal cord, corresponding to the abnormal hyperintense signal seen on T2-weighted sequences [^6^]. Flow voids in the epidural space may also be observed [^5^].
Post-contrast MRI, acquired in the flexion position, may reveal crescent-shaped enhancement of the posterior epidural space on fat-suppressed T1-weighted images [^7^]. This enhancement is thought to be related to the dilated epidural veins and disrupted blood-brain barrier in the affected area [^7^].
In addition to MRI, myelography can also be used to evaluate patients with suspected Hirayama disease. Myelograms and flexion-extension MR images may demonstrate the forward migration of the posterior wall of the dura mater and the dynamic compression of the spinal cord during flexion [^6^].
Several conditions may mimic the clinical and radiological features of Hirayama disease. These include but are not limited to, motor neuron diseases such as amyotrophic lateral sclerosis (ALS), brachial plexopathies, and cervical spondylotic myelopathy. A thorough clinical evaluation, along with the characteristic radiological findings, can help differentiate Hirayama disease from other conditions.
The management of Hirayama disease primarily focuses on preventing further progression of the disease and improving quality of life. Conservative measures, such as the use of cervical soft braces, are the first-line management strategy [^7^]. These braces help stabilize the neck and prevent excessive flexion, reducing the dynamic compression of the spinal cord. Surgical interventions, such as anterior cervical decompression and fusion, may be considered in cases where conservative measures fail or in the presence of severe neurological deficits [^7^]. It is important to note that Hirayama disease is a self-limiting condition, and the disease progression usually arrests after 3-5 years [^7^].
Hirayama disease is a rare neurological disorder that primarily affects young Asian males. It is characterized by progressive weakness and atrophy of the distal upper limbs, with sparing of the brachioradialis muscle. MRI plays a crucial role in the diagnosis and evaluation of Hirayama disease, allowing for the visualization of structural abnormalities and dynamic changes during neck flexion. The characteristic findings include forward migration of the posterior dura, compression of the spinal cord, and enlargement of the posterior epidural space. With prompt recognition and appropriate management, patients with Hirayama disease can experience improved outcomes and a better quality of life.
References:
Keizo Hirayama et al. "Focal cervical poliopathy causing juvenile muscular atrophy of distal upper extremity: a pathological study," Journal of Neurology, Neurosurgery & Psychiatry 2006;77: 1020-1026.
Tushar Kalekar et al. "Cervical Spine Magnetic Resonance Imaging Findings in Hirayama Disease," Cureus 2023;15(8):e40015.
Abel Thomas Oommen et al. "Classical Hirayama Disease Presenting as Progressive Spastic Quadriparesis," Annals of Indian Academy of Neurology 2023;26(3):308.
Bhargavi Paladi et al. "Role of Dynamic Magnetic Resonance Imaging in Hirayama Disease, a Rare Motor Neuron Disease," Cureus 2022;14(8):e40015.
Monali Raval et al. "Hirayama's Disease - Importance of Flexion Magnetic Resonance Imaging," Journal of Postgraduate Medicine 2011;57(1):48-50.
V.T. Lehman et al. "Cervical Spine MR Imaging Findings of Patients with Hirayama Disease in North America: A Multisite Study," AJNR Am J Neuroradiol 2013;34(2):451-456.
Jakhere S, Wagh V. "Hirayama's disease: The importance of flexion magnetic resonance imaging," Journal of Postgraduate Medicine 2011;57(1):48-50.