Key-words:
Cervical flexion myelopathy - Hirayama disease - instrumentation without fusion
Introduction
Hirayama disease (HD) is a sporadic juvenile muscular atrophy which affects muscles
of forearm and hand. This rare entity was first described by Hirayama in the year
1959.[[1]] HD is mainly seen in young males of Asian ethnicity[[2]],[[3]],[[4]] in the second and third decades of life. There are sparse data regarding the exact
incidence and prevalence of HD. According to a study by Tashiro et al.,[[4]] they identified 333 cases based on two questionnaire-based surveys. The other data
are still anecdotal and limited to case series and reports as the one described by
Huang et al.,[[5]] of 40 patients. The cases are not restricted only from Asia and there are reports
from Europe and America too. It is an insidious onset slowly progressive disease which
becomes self-limiting over a period. Sensory, autonomic system involvement and upper
motor neuron signs are rare.[[6]]
Etiology and pathogenesis of HD mainly involve lower cervical cord damage due to stretching
of tight cord in the spinal canal during neck flexion. Repeated neck flexion causes
gradual cord changes which include ischemia of anterior horn cells (AHCs) and cord
atrophy. This causes the persistence of symptoms such as handgrip weakness, difficulty
in writing and other fine activities. Younger patients are easily disabled and notice
their symptoms early in the course of the disease.
The treatment of HD involves cervical collar immobilization in neck extension; however,
this requires compliance with collar for a prolonged duration. Surgical fixation to
maintain neck extension without decompression or fusion is another treatment modality
described.
Case Report
An 18-year-old male patient presented to our tertiary care hospital with complaints
of weakness in the right hand and forearm and difficulty in performing fine activities
such as writing and buttoning-unbuttoning. Symptoms were insidious in onset and gradually
progressed over the period of 1 year. The patient did not have neck pain, tingling
numbness in hand, difficulty in walking, dysphagia, or bowel bladder involvement.
There was no history of trauma. He did not have any other medical comorbidities.
Clinical examination revealed painless neck movements. There was marked wasting of
hand muscles with weakness of handgrip on the right side. There was weakness of finger
abduction and adduction. Wrist flexion was Medical Research Council (MRC) Grade 3
on the right side. Power in the rest of the upper limb and both lower limbs was Grade
5. There was no history of involuntary movements. Bladder and bowel functions were
intact. The posterior column, cerebellum, and cranial nerve functions were intact.
Blood investigations did not reveal any significant abnormality. Radiological investigations
in the form of cervical spine radiograph and magnetic resonance imaging (MRI) were
done. Plain radiographs revealed loss of cervical lordosis. Dynamic MRI in the position
of neck flexion, extension and neutral position was done. MRI in neutral position
[[Figure 1]] showed doubtful intramedullary hyperintensity in T2-weighted sections. Flexion
MRI [[Figure 2]] showed forward displacement of posterior dural sac and revealed a T2-weighted hypointense
space posterior to the dural sac which was getting corrected on neck extension [[Figure 3]]. The posterior space likely revealed posterior dural venous plexus and disappeared
on the neck extension. The nerve conduction studies/electromyography (EMG) findings
were in synchronicity with the MRI report with signs of chronic motor axon denervation
with likely site being the AHC [[Figure 4]]. Clinical and radiological examination confirmed the presumptive diagnosis of HD
due to the typical site of involvement at the AHC and forward shift of posterior dural
sac on flexion MRI. The differential diagnosis of peripheral nerve entrapment and
thoracic outlet syndrome was ruled out clinically and EMG studies. The patient received
conservative management for 6 months in the form of hard cervical collar. The patient
did not improve symptomatically and a poor compliance to the collar was suspected.
Conservative management has been the mainstay of treatment in HD. However, in this
case, we highlight the importance of posterior fixation without an attempt for fusion.
Figure 1: Magnetic resonance imaging in neutral position
Figure 2: Posterior subdural sac is displaced forward on neck flexion, prominent epidural space
noticed
Figure 3: Correction of forward displacement of the posterior dural sac in extension magnetic
resonance imaging
Figure 4: Nerve conduction studies/electromyography showing site of localization at the anterior
horn cell
Operative intervention was planned in the form of posterior fixation using lateral
mass screws to ensure limitation of neck flexion. No fusion or posterior decompression
was planned as the disease has a self-limiting course after reaching a plateau. Under
general anesthesia, Gardner-Wells tongs were applied and the patient was kept in prone
position. Weights were attached to the tongs and cervical lordosis was confirmed on
fluoroscopy. In the absence of a Mayfield head holder, tongs with minimal traction
provide adequate stabilization of the head on the frame during surgical fixation.
A midline posterior approach was taken. Skin, subcutaneous tissue, and fascia were
incised; paraspinal muscles were lifted subperiosteally. Lateral mass screws were
passed at C4, C5, and C6 vertebral levels. A contoured rod was passed to maintain
neck position in lordosis [[Figure 5]]. Position, length of screws, and neck alignment were confirmed on C-arm. The standard
closure was done in layers over a negative suction drain. Postoperatively, the patient
was given Philadelphia brace to maintain the neck position for 1 month [[Figure 6]]. Neurological improvement was noticed postoperatively and at 1 year follow-up patient
has MRC Grade 5 motor power in wrist flexion and handgrip has improved along with
maintained cervical lordosis.
Figure 5: Postoperative plain radiograph
Figure 6: Postoperative brace wear to prevent neck flexion
Discussion
HD is a rare disease affecting primarily young men in second and third decades of
life. It has been called differently as Juvenile atrophy of the distal upper extremity,[[1]] monomelic amyotrophy,[[6]] or juvenile asymmetric segmental spinal muscular atrophy. HD is characterized by
the insidious onset of unilateral or asymmetric atrophy of hand and forearm with sparing
of brachioradialis muscle giving a characteristic appearance of oblique amyotrophy[[7]] involving C7, C8, and T1 myotomes. It is thought to be a kind of cervical myelopathy
related to flexion movement of the neck.[[8]] HD differs from classical types of motor neuron disease[[9]] because of its nonprogressive course and pathologic finding of chronic microcirculatory
changes in the territory of anterior spinal artery supplying the anterior horn cells
of lower cervical cord.[[10]] The etiopathogenesis of this disease is attributed to forward displacement of posterior
wall of lower cervical dural canal in neck flexion causing marked and asymmetric flattening
of lower cervical cord.[[8]] Normal subjects may also show a forward shift of posterior dura in neck flexion
however flattening or distortion of the cervical spinal cord does not occur and the
average anterior displacement is <1 mm. The general course of the disease is benign
with moderate-to-severe functional impairment. Patients with HD are not known to have
abnormal anterior pathologies such as spondylotic spurs or disc herniations; therefore,
removing any of these normal structures is not indicated in the management of these
patients. The anterior shift of the posterior dura leads to engorgement of the posterior
epidural plexus however an increased epidural pressure is not reported in these cases.
The common presentation in these cases starts with a unilateral upper extremity involvement
although bilateral involvement and lower limbs involvement is also rarely reported
as anecdotal case reports. Some uncommonly reported symptoms are coarse irregular
tremors in the affected hands (minipolymyoclonus) and transient worsening of symptoms
on exposure to cold. There is absence of cranial nerve involvement or pyramidal tract
involvement. Cerebellar involvement or bowel bladder dysfunction is not a typical
finding in HD and should arouse suspicion to rule out other etiologies.
This patient presented to us with symptoms that were analogous to the diagnosis of
HD which were confirmed with radiological imaging in the form of dynamic MRI. He already
received treatment in the form of cervical collar which requires strict patient compliance
with collar wear for a long duration. This allows continuation of microtrauma in case
the patient is noncompliant leading to permanent cord damage.
Surgical intervention remains an option in patients who do not improve with cervical
collar.[[11]],[[12]] Surgical treatment modalities include posterior cervical fixation without decompression
and fusion, as described by Xu et al.[[13]] To ensure limitation of neck flexion cervical spine fixation in lordotic position
was done without decompression and fusion in our patient. It has a static course after
an initial spurt of 2–5 years. Hence, it should be ensured that neck flexion is restricted
to a minimum and surgical instrumentation without fusion may be an effective way to
achieve the desired outcome. The instrumentation can later be reversed and hence adequate
neck range of motion can be achieved once instrumentation is removed since there was
no attempt of fusion during the surgery.
Cervical duraplasty with tenting sutures through laminoplasty[[14]] is another described surgical technique. This technique leads to spinal cord decompression
with the preservation of cervical alignment and local physiological motion in young
patients with HD without major complications. Increased immunoglobulin E levels are
often found associated with HD, which may lead to connective tissue changes partly
explaining the clinical findings.
Conclusion
HD is a self-limited pathology, but it has to be differentiated early from other diseases
that could determinate myelopathy and amyotrophy to establish a correct therapy and
limit impairment of motor power. MRI is very important to confirm clinical suspect
of HD, and a standardized MRI protocol using axial and sagittal images in both neutral
and flexed position is needed to make diagnosis and to follow-up affected patients.
Declaration of patient consent
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In the form the patient(s) has/have given his/her/their consent for his/her/their
images and other clinical information to be reported in the journal. The patients
understand that their names and initials will not be published and due efforts will
be made to conceal their identity, but anonymity cannot be guaranteed.
