
==== Front
Ann Indian Acad Neurol
Ann Indian Acad Neurol
AIAN
Ann Indian Acad Neurol
Annals of Indian Academy of Neurology
0972-2327
1998-3549
Wolters Kluwer - Medknow India

39167476
AIAN-27-364
10.4103/aian.aian_236_24
Original Article
Hirayama Disease: Neutral and Flexion Magnetic Resonance Imaging Manifestations and Single Tertiary Care Center Analysis on 3T Scanner
Kaira Pankaj
Kaira Vaanika 1
Verma Sameer R.
Kumar Sunil 2
Department of Radiodiagnosis, Shri Ram Murti Smarak Institute of Medical Sciences, Bareilly, Uttar Pradesh, India
1 Department of Oncopathology, The Gujarat Cancer and Research Institute, B. J. Medical College, Ahmedabad, Gujarat, India
2 Department of Neurology, Shri Ram Murti Smarak Institute of Medical Sciences, Bareilly, Uttar Pradesh, India
Address for correspondence: Dr. Pankaj Kaira, Department of Radiodiagnosis, Shri Ram Murti Institute of Medical Sciences, Bareilly - 2432 002, Uttar Pradesh, India. E-mail: pankajkaira1982@gmail.com
Jul-Aug 2024
21 8 2024
27 4 364370
28 3 2024
14 6 2024
17 6 2024
Copyright: © 2024 Annals of Indian Academy of Neurology
2024
https://creativecommons.org/licenses/by-nc-sa/4.0/ This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms.
Background:

Hirayama disease (HD) is a rare benign type of cervical cord myelopathy occurring commonly in young males as unilateral or bilateral asymmetrical amyotrophy of the hand and forearm muscles in C8–T1 distribution. Magnetic resonance imaging (MRI) is the best technique for the evaluation and imaging of this entity.

Materials and Methods:

This is a retrospective review of cervical magnetic resonance images of patients that were taken for clinically suspected and diagnosed HD on 3T MRI in postcontrast neutral and flexion (30°–40°) positions from July 2019 to January 2024 at Shri Ram Murti Smarak Institute of Medical Sciences, Bareilly.

Results:

Fourteen patients included in the study were males less than 34 years of age. MRI findings of cord atrophy in the lower cervical region/cervico-dorsal junction, abnormal cervical curvature, loss of attachment of the dorsal dural sac and subjacent laminae with anterior displacement, and a prominent intense enhancing posterior epidural space were observed in all 14 patients. The minimum anteroposterior cord diameters in the neutral and flexion positions were 2.9 and 2.8 mm, respectively (mean thickness of laminodural space on flexion – 5.2 mm). Other MRI findings showed variable representations.

Conclusions:

Flexion-position MRI has emerged as the gold standard for establishing and validating the diagnosis of HD in clinically suspected cases and should be an essential part of the protocol for the screening of clinically suspected cases of HD to aid in early treatment and therapeutic intervention. Complimentary newer sequences such as the Three-dimensional (3D)-Constructive interference in Steady State (CISS)/Fast Imaging Employing Steady-state Acquisition Cycled Phases (FIESTA-C) may reinforce better appreciation of epidural flow voids.

Hirayama disease
loss of attachment
magnetic resonance imaging
neutral and flexion
==== Body
pmcINTRODUCTION

In 1959, Hirayama et al.[1] identified juvenile muscular atrophy of unilateral upper extremity in a Japanese patient, which led to the initial description of Hirayama disease (HD). Since then, it has been known by several names. It typically occurs in young males in their second to third decade and is most commonly seen in Asian countries like Japan, Malaysia, and India, as well as in Europe and North America.[2]

HD is a benign, nonprogressive juvenile spinal muscular atrophy that is characterized by a unilateral or asymmetric wasting that develops slowly, sparing the brachioradialis muscle and causing weakness in the hand and forearm muscles (oblique amyotrophy). It has maximum effect on the C8–T1 segmental myotomes.[3] The majority of individuals have unilateral amyotrophy, a few people have bilateral asymmetry, and symmetric amyotrophy is relatively rare.[4] Although the incidence in the lower limb is extremely rarer, monomelic amyotrophy of the lower limb has been described in the literature as a clinically localized variation of spinal muscular atrophy.

Although the exact etiopathogenesis is unknown, the most widely accepted theory proposes that repeated flexion-induced chronic microcirculatory alterations in the anterior spinal artery area lead to ischemia and necrosis of the anterior horns of the lower cervical cord.[356] Excessive forward displacement of detached dorsal dura, together with significant and frequently asymmetric compression and flattening of the lower cervical cord result from repeated and sustained flexion.

Cord atrophy can be a presenting feature of many other disorders, such as motor neuron disease, amyotrophic lateral sclerosis, spinal cord tumors, etc., however, differentiation from HD needs to be done as it is a self-limiting nonprogressive entity.

The literature describes a range of diagnostic magnetic resonance imaging (MRI) characteristics for this infrequent disease. Flexion MRI, in particular, increases the conspicuity of the posterior dura’s loss of attachment (LOA) and enhances the epidural venous plexus, which aids in the accurate identification of HD and distinguishes it from its mimics.

Studies documenting HD from its initial description are available; however, data collection and literature from emerging nations such as India remain patchy. Therefore, the purpose of this study is to contribute to the body of knowledge by assessing the different cervical spine MRI findings of HD in neutral and flexion positions in the North Indian population using a 3T MRI scanner on clinically suspected and confirmed cases of HD in this region of the world.

MATERIALS AND METHODS

We conducted a retrospective study with a review of cervical magnetic resonance (MR) images of 17 patients on the hospital information system who underwent imaging evaluation for clinically suspected and diagnosed HD on a 3T MRI scanner in postcontrast neutral and flexion (30°–40°) positions, performed from July 2019 to January 2024 at Shri Ram Murti Smarak Institute of Medical Sciences, Bareilly.

Written approval was taken from the institutional ethics committee for this retrospective study (Ref. No: SRMS IMS/ECC/2024/07), and no ionizing radiation was involved. Informed consent was waived.

Inclusion and exclusion criteria

Inclusion criteria:

Patients of all age groups who had a clinical suspicion or diagnosis of HD underwent MRI.

Exclusion criteria:

Patients who had not undergone flexion MRI

Patients with inconclusive imaging findings for HD

Imaging suggesting alternate diagnoses were excluded.

Method of data collection

We retrieved clinical data, including patient age, results of electrophysiology study, and MR images along with imaging reports, from the hospital electronic medical records by using the keywords “Hirayama” and “flexion MRI.”

Seventeen patients fulfilled the initial search criteria for the clinical suggestion (suspicion and diagnosis) of HD, and the pre- and post-contrast MR images in neutral and flexion positions of these patients were evaluated. Three patients were excluded from the study as two patients had no imaging features to suggest HD (disc herniations/disc osteophyte complex causing compressive myelopathy), while in the third patient, flexion MRI was not done. Fourteen cases with a diagnosis of HD were included in the study.

All the patients evaluated were males aged between 17 and 34 years with a mean age of 21 years and mode age of 20 years at the time of study. The most common age group involved in our study was 16–20 years (71.4%), followed by 21–25 years (21.4%). Neurophysiologic workup included nerve conduction study (NCS) and electromyography (EMG) to identify neurogenic changes.

MRI protocol

MRIs were performed on all patients using a 48-channel, 3T wide-bore MRI scanner (Magnetom Skyra, Siemens, Erlangen, Germany). The study was conducted in both neutral and flexion positions, along with a post-contrast study. In addition to these, a complementary sagittal 3D-CISS/FIESTA-C sequence was obtained in the neutral and flexion positions with axial reconstructions.

The following features were evaluated: (a) cord atrophy in the lower cervical region and cervico-dorsal junction with reference to minimum anteroposterior (AP) cord diameters in neutral and flexion positions, (b) intramedullary T2 hyperintensity, (c) abnormal cervical curvature, (d) asymmetric cord flattening, (e) LOA between the posterior dural sac and the subjacent laminae on flexion, (f) anterior displacement of the dorsal dura on flexion, (g) presence of prominent epidural flow voids on flexion, (h) enhancement of posterior epidural venous plexus as a crescentic area with flow voids within on postcontrast T1-weighted MRI (flexion-position MRI), and (i) thoracic extension of the enhancing epidural component.

Based on the definitions listed in the literature below, the aforementioned features were identified. The cord between C4 and C7 was defined as the lower cervical cord.[7] As per the classification given by Guigui et al.[8] and Batzdorf and Batzdorff,[9] the cervical curvature is deemed normal when the dorsal aspect of the vertebral bodies from C3 to C6 is anterior to the line drawn from the dorsocaudal aspect of the body of the C2 vertebra to the dorsocaudal aspect of the C7 vertebra, whereas it is deemed abnormal (straight or kyphotic) when part or all of the dorsal aspects of the vertebral bodies from C3 to C6 meet or cross through this line [Figure 1].[7101112]

Figure 1 Neutral position sagittal T2WI MRI showing loss of cervical lordosis and localized lower cervical cord atrophy (arrows). T2WI axial MRI showing anteroposterior pear-shaped asymmetric cord flattening, more toward the left side, and intramedullary bilateral hyperintensities. MRI = magnetic resonance imaging, T2WI = T2-weighted image

Transverse MR images were used to define asymmetric cord flattening as a flattened cord without a reduced or obliterated surrounding subarachnoid space. An elliptical spinal cord was considered normal, while a triangular configuration was seen as symmetrical cord flattening. A pear-shaped spinal cord was assumed to be experiencing asymmetric cord flattening [Figure 1].[71112]

Reduction in cord size relative to the normal cord above and below the affected level was defined as localized cord atrophy on sagittal MR images and further validated on axial MR images[71012] It was recorded as symmetrical or asymmetrical [Figure 1].

Axial T2 spin echo image was used to measure LOA between the posterior dural sac and the adjacent lamina on each side from C4 to C6 levels as per the method described by Chen et al.[13] The lamina was divided equally into three parts, with LOA greater than one third between the subjacent lamina and the posterior dural sac considered as significant.[121415]

Anterior displacement of the dural sac (LDS) and the appearance of enhancing posterior epidural component along with flow voids were noted in the flexion study.[710] LDS was measured at the maximum thickness of the dural detachment and corresponds to the enhancing posterior epidural component on postcontrast images (better visualized on 3D-CISS/FIESTA-C sequence) [Figure 2]. We also obtained the minimum AP diameters of the cervical cord in axial images, both in neutral and flexion MR imaging at the site of maximum forward shifting of the posterior dural sac. The thoracic extension of the epidural component was recorded. Intramedullary high signal intensity was noted and considered noncompressive only if patent subarachnoid space was appreciated.[71213]

Figure 2 Sagittal and axial T2W MRI and T1W post-gadolinium contrast images in flexion positions showing anterior displacement of the dorsal dura causing thecal sac compression, with prominent flow voids in enlarged posterior epidural space with severe increase in the laminodural distance (arrows). Thoracic extension of the enhancing epidural crescent is seen. MRI = magnetic resonance imaging, T1W = T1 weighted, T2W = T2 weighted

RESULTS

All patients presented with an insidious-onset illness. Upper limb weakness was the most common symptom, which was unilateral in 11 and bilaterally asymmetric in three patients. Other common presenting complaints and clinical findings were hand and forearm muscle wasting, minipolymyoclonus, increased weakness during cold, tremors, and fasciculation.

Electrophysiologic studies

Both NCS and EMG were performed in all patients to assess the function and integrity of the peripheral nerves and muscles.

NCS: Compound muscle action potentials (CMAPs) were reduced in the median and ulnar nerves in many patients (ulnar nerve being more affected than median nerve, involving both in six patients and only the ulnar nerve in two patients). Despite the reduced CMAPs, distal latencies and F-wave latencies were within the normal range in majority of the patients, except for two patients showing minimal increase in latency in ulnar nerve. Conduction velocities were normal across the tested nerves. Sensory nerve conduction studies revealed absolutely normal results in all patients.

EMG: Signs of active denervation, such as fibrillations and fasciculations, were seen, fibrillations in six patients and fasciculations in eight patients. Neurogenic changes were seen in all patients, predominantly in the C7, C8, and T1 myotomes, indicating chronic denervation. In addition, C7 myotome muscles were commonly involved. These changes suggest long-standing damage to the motor neurons that supply these muscle groups. One of the patients with extensive cord atrophy up to D3 vertebral level also showed involvement of muscles in C5–C6 myotomes (deltoid and biceps brachii muscles). The brachioradialis muscle was spared in all the patients.

MRI evaluation

All the 14 patients evaluated showed cord atrophy in the lower cervical region and cervico-dorsal junction (the extent of cord atrophy was from C4 to D1 vertebral levels, with one patient displaying extended atrophy up to D3 vertebral level; involvement of the C5–C7 levels was seen in majority of the patients), abnormal cervical curvature as loss of cervical lordosis, LOA of the dorsal dural sac and subjacent laminae with anterior displacement of the dorsal dura compressing the thecal sac on flexion, and a prominent crescent-shaped intense enhancement in posterior epidural space as increased laminodural space. Salient MRI features are shown in Figures 3 and 4. In the neutral and flexion positions, the minimal AP cord diameters were 2.9 and 2.8 mm, respectively. The laminodural space on flexion had a mean thickness of 5.2 mm, with minimum and maximum thicknesses of 1.7 and 7.8 mm, respectively. Cord flattening was seen in all the patients, which was asymmetric in 11 (78.5%) and symmetric in three (21.5%). Prominent epidural flow voids were seen in 11 patients (78.5%). Intramedullary cord T2-weighted (T2W) hyperintensities were noted in nine patients (64.2%). Thoracic extension of enhancing epidural component was found in 13 patients (92.8%) [Table 1].

Figure 3 Neutral position sagittal and axial T2-weighted MR images (a and b) show localized lower cervical cord atrophy with bilateral symmetrical intramedullary hyperintensities. Flexion MR T2-weighted images (c and d) show anterior displacement of the dorsal dura with obliteration of subarachnoid spaces and flow voids seen in the posterior epidural space. Post-gadolinium fat-suppressed sagittal and axial T1-weighted flexion MR images (e and f) show an enhancing epidural venous plexus with thoracic extension and flattening of the cord. MR = magnetic resonance

Figure 4 Neutral position sagittal T2-weighted MR image (a) shows straightening of the cervical spine curvature. No intramedullary hyperintensities were seen even on axial images (b). Flexion MR T2-weighted image (c) shows an enlarged posterior epidural space with multiple flow voids. Post-gadolinium fat-suppressed sagittal and axial T1-weighted flexion MR images (d and e) show an enhancing epidural venous plexus with flow voids and thoracic extension causing asymmetric flattening of the left hemicord. MR = magnetic resonance

Table 1 MRI features

MRI feature	Present study No. (%)	Sonwalkar et al. (2008) No. (%)	Raval et al. (2010) No. (%)	Hassan et al. (2012) No. %	Boruah et al. (2018) No. %	Rathore et al. (2021) No. %	Kaur et al. (2022) No. %	Paladi et al. (2022) No. %	
Total number of patients	14	8	9	11a	45	13	17	15	
Cord atrophy in the Cord atrophy in the lower cervical region and cervico-dorsal junction	14/14 (100)	8/8 (100)	9/9 (100)	9/11 (82)	27/45 (60)	13/13 (100)	17/17 (100)	12/15 (80)	
IntramedullaryT2 hyperintensity	9/14 (64.2)	3/8 (37)	4/9 (44)	2/11 (18)	16/45 (35.5)	11/13 (84.6)	6/17 (35.2)	8/15 (53.5)	
Abnormal cervical curvature (loss of cervical lordosis)	14/14 (100)	6/8 (75)	9/9 (100)	10/11 (91)	39/45 (86.6)	9/13 (69.2)	10/17 (58.8)	14/15 (93.3)	
Asymmetric cord flattening	11/14 (78.5)	6/8 (75)	9/9 (100)	11/11 (100)	31/45 (61.8)	6/13 (46.1)		-	
LOA between posterior dural sac and subjacent laminae on flexion	14/14 (100)	4/8 (50)	9/9 (100)	9/10 (90)	45/45 (100)	9/13 (69.2)	17/17 (100)	15/15 (100)	
Anterior displacement of the dorsal dura on flexion	14/14 (100)	6/8 (75)	9/9 (100)	9/10 (90)	45/45 (100)	13/13 (100)	11/17 (64.7)	15/15 (100)	
Prominent epidural flow voids on flexion	11/14 (78.5)	4/8 (50)	4/9 (44)	9/10 (90)	45/45 (100)	8/13 (61.5)	13/17 (76.4)	13/15 (86.6)	
Enhancing epidural component on postcontrast flexion-position MRI	14/14 (100)	6/8 (75)	9/9 (100)	10/10 (100)	45/45 (100)	13/13 (100)	16/17 (94.1)	15/15 (100)	
Thoracic extension of enhancing epidural component	13/14 (92.8)	5/8 (62.5)	4/9 (44)	-	-	5/13 (38.4)	-	-	
LOA=loss of attachment, MRI=magnetic resonance imaging. aEleven patients underwent routine neutral position MRI, 10 underwent flexion contrast MRI

DISCUSSION

HD was originally described in 12 cases as juvenile muscular atrophy of unilateral upper extremity when it was first conceptualized in 1959 in Japan by Hirayama et al.[1] Clinically, the condition observed in these patients could be distinguished from progressive and degenerative motor neuron diseases, such as spinal progressive muscular atrophy and amyotrophic lateral sclerosis.

It primarily affects young males in the 15–25 years age group. But reports of the condition in younger and older age groups also exist.[1416] All the patients in our study were male; majority of them (71.4%) were aged between 16 and 20 years, with the remaining patients being under 25 years. Only one patient was in his 30s.

Most of the reported cases are from Asia, Japan, India, and China, although there have been some reports from other countries including North America and Europe.[21416] The clinical symptoms include an insidious-onset weakness, unilateral or asymmetric bilateral upper extremity muscular atrophy, and cold paresis without involvement of the sensory or pyramidal tracts.[5611] About 70% of individuals show signs of disease progression within 3 years, and approximately 95% stabilize 5 years after disease onset.[2]

The electrophysiologic studies in our study revealed active and chronic denervation of predominantly C7–T1 myotomes and absence of sensory involvement. The electrophysiologic studies in HD typically reveal reduced CMAPs with normal to minimal increase in latencies and normal conduction velocities, normal sensory NCS, and EMG findings of both active and chronic denervation in specific cervical myotomes (C7, C8, and T1), with the upper cervical myotomes usually unaffected or less commonly involved as seen in the variant of the disease. The focal C7–T1 involvement differs from widespread involvement as in motor neuron disease. The C7–T1 segment involvement is predominantly seen in Asian countries; however, studies from Western countries show predominant involvement of C5–C7 segments.

The self-limiting character of this condition and the pathologic evidence of chronic microcirculatory alterations in the anterior horns of the lower cervical cord distinguish it from the classical type of motor neuron disease. Numerous hypotheses have been proposed and discussed about the etiopathogenesis of HD.

Kikuchi et al.,[17] in 1987, first proposed that an imbalanced growth causes disproportion in the lengths of the vertebral column and the spinal canal contents, resulting in a tight dural sac.

The dural sac’s excessive shortening may be exacerbated during the juvenile development spurt, according to a study by Toma and Shiozawa. There have been suggestions that the disparate growth rates between male and female patients are the reason for the male preponderance of HD.[18]

The spinal dura mater in a healthy spine is a loose sheath that is attached to the periosteum and the nerve roots at two different locations in the vertebral canal: at the foramen magnum, C2, and C3 and at the coccyx. Many transverse folds in the loose, flaccid dura mater typically serve as a compensatory mechanism for the cervical canal’s increased length during flexion. Conversely, in patients suffering from HD, the posterior dural sac may separate from its subjacent lamina and there may be variable degrees of abnormal cervical curvature caused by the tight dural sac. Microcirculatory disturbances in the territory of the anterior spinal artery in the lower cervical spinal cord result from the tight dural sac’s inability to compensate for the increased length of the posterior wall during neck flexion. As a result, it is displaced anteriorly and the cord is compressed against the posterior margin of adjacent vertebral bodies and eventually causes necrosis of the anterior horns with resultant gliosis and localized cord atrophy at the lower cervical region.[5712171920]

In 2010, Ciceri et al.[21] proposed that one of the causes of spinal cord ischemic changes might be venous congestion, which is secondary to impaired venous drainage toward the jugular veins occurring during flexion.

Conventional radiographic studies of the cervical spine (X-ray and fluoroscopy) in HD have a limited role as they may only show loss of cervical lordosis, which is a nonspecific finding and can be seen in many other entities.[571020] MRI with flexion contrast study is the gold standard of diagnosis.

LOA between the posterior dural sac and the subjacent lamina in a neutral position, anterior shifting of the posterior wall of the cervical dural canal, enhancing epidural component in the lower cervical and thoracic regions, and prominent posterior epidural flow voids suggestive of dilated epidural venous plexus on flexion studies are reported as highly suggestive for the diagnosis of HD. Other MRI features that may be seen are symmetric or asymmetric localized lower cervical cord atrophy, abnormal cervical curvature, asymmetric cord flattening, and intramedullary T2 hyperintensity.[57101112132022]

Raval et al.[5] proposed that the use of the 3D-FIESTA study in flexion may obviate the need for a contrast-enhanced study as flexion 3D-FIESTA in these patients revealed prominent flow voids within the hyperintense crescentic epidural mass in all patients. Gupta et al.[23] also proposed the use of 3D-CISS for better visualization of the epidural flow voids on MRI, which was supported by our study. But most existing literature suggests the need for flexion MRI in the diagnosis of HD.

In our study, localized lower cervical cord atrophy was seen in all cases of HD. In earlier studies, Pradhan,[4] Raval et al.,[5] Kaur et al.,[10] and Sonwalkar et al.[12] also found focal cord atrophy in the neutral neck position on MRI in 100% of their cases, while Boruah et al.[20] have reported it only in 60% of cases and Hassan et al.[7] in 82% cases.

Intramedullary altered signal intensity within the cord was seen in nine (64.2%) of our cases as hyperintensities on T2. It was found to be extremely low in the study by Hassan et al.[7] (18%); it was about 35.2% in the study of Kaur et al.,[10] 35.6% in the study of Boruah et al.,[20] and 44% in the study of Raval et al.[5] However, in contrast, Rathore et al.[11] reported it in 84.6% of their cases. Intramedullary high signal intensity represents severe ischemic change or gliosis in the susceptible areas, but its incidence is lower than that of localized lower cervical cord atrophy.[22]

Abnormal cervical curvature as straightening of the cervical spine was seen in all 14 (100%) cases in our study, appearing in tandem with a study done by Rawal et al.[5]; however, Rathore et al.[11] reported it in only 69.2% of their cases, Sonwalkar et al.[12] in 75% of their cases, and Hassan et al.[7] in 91% of their cases.

Asymmetric cord flattening was noted in 11 (78.5%) of our cases compared to 46.1% in the study done by Rathore et al.[11] Boruah et al.[20] reported a prevalence of 61.8%, while Hassan et al.[7] and Rawal et al.[5] observed it in all of their studied patients.

LOA of the dorsal dural sac and subjacent laminae with anterior displacement of the dorsal dura compressing the thecal sac on flexion and a prominent crescent-shaped intense enhancement in the posterior epidural space were observed in all 14 patients (100%). This LOA of the posterior dura has been reported in various previous studies, with 100% in some of them[51020] but only in 50% of their cases by Sonwalkar et al.[12] An efficacy of 100% was reported in the study of Lehman et al.,[24] but with a lower sensitivity and 29% false-negative rates of LOA in few patients. Lai et al.[25] observed that the laminodural space representing forward displacement of the dural sac was also seen in 46% of healthy subjects without any spinal cord compression. Boruah et al.[20] reported LDS can range from 3 to 9.8 mm, with a mean distance of approximately 5.9 mm. In the study by Paladi et al.,[26] at the maximum forward shift of the cord, LDS ranged from 3.1 to 7.0 mm, with a mean of 5.38 ± 1.13 mm. However, our study showed this distance within the range of 1.7–7.8 mm with a mean of approximately 5.2 mm. This is lower than the distance measured in the study performed by Boruah et al.[20] The most common site for the maximum forward displacement of the dura in our study was at C6. The anterior dural shift becomes less prominent with the chronic stage of the disease and with old age.

Prominent epidural flow voids on flexion were seen in 11 patients (78.5%) in our study, all (100%) patients in the study by Boruah et al.,[20] and in 86% of cases in the study of Paladi et al.[26] However, it was less in other studies; Rathore et al.[11] reported it in only 61.5% of their cases and Rawal et al.[5] reported it in 44% of their cases.

Thoracic extension of enhancing epidural component was found in 13 patients (92.8%). These characteristics have been reported in only a few studies and that too with a lower frequency as it is an unusual finding. It was found to be as low as 38.4% in the study by Rathore et al.,[11] and reported as about 44% by Raval.[5]

Our findings are in greater conformity with the findings of Rawal et al.,[5] Hassan et al.,[7] and Paladi et al.[26] than that of Sonwalkar et al.[12] Such variation is likely due to the difference in patient characteristics and the extent of involvement by the disease.

As HD is considered a self-limiting disease, the mainstay of treatment consists of reducing repeated trauma to the cervical cord by avoiding repeating neck flexion using a cervical collar for 3–4 years to halt further progression. Its application at an early stage of the disease has been advocated with a good response.[202728] Electrophysiologic studies, especially of F wave and motor evoked potentials, are thought to be useful indicators to start and stop cervical collar therapy.[28] Good prognosis is seen in patients with a shorter duration of illness and with no or mild cord atrophy in a neutral neck position.[27] Even surgical interventions such as cervical decompression and fusion with or without duraplasty, cervical duraplasty without cervical fusion, and reconstructions with tendon transfers may be advised in selected patients.[27282930] Hence, early recognition of HD is necessary because the patient can be advised to avoid or limit neck flexion movements, which helps in arresting progressive muscular weakness in the early stage of the disease. So, to avoid serious dysfunction, a high index of clinical suspicion along with knowledge of the aforementioned findings on flexion and neutral MRI is necessary for early and accurate diagnosis.

We realize that our study has limitations. Due to the disease’s uncommon prevalence, one of the primary disadvantages is the small sample size. No control group was provided to compare the characteristics with. The study’s retrospective design is another drawback.

CONCLUSION

To conclude, MRI in the flexion position is the gold standard for HD. Although certain hallmark imaging traits like asymmetrical cord atrophy, intramedullary T2W hyperintensities, abnormal cervical curvature, and LOA of posterior dura can be seen on neutral MRI as well, these findings are not seen in all cases. Hence, addition of flexion MRI as an essential part of the protocol for the screening of clinically suspected cases of HD increases diagnostic confidence and aids in early treatment and intervention. Newer sequences such as 3D-CISS/FIESTA-C could be further added as an essential part of the screening protocol in patients with suspected HD.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.
==== Refs
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