Keywords
Hirayama disease - granuloma formation - ReDura - posterior cervical techniques -
MRI spine
Introduction
Monomelic amyotrophy, popularly known as Hirayama disease, is a neurological disorder
causing asymmetric segmental muscular atrophy of the distal upper extremities commonly
affecting young Asian males.[1] Characteristic clinical and dynamic magnetic resonance imaging (MRI) spine findings
help diagnose the disease. Conservative management is offered for milder forms, while
surgery is preferred for progressive disease. The two surgical approaches include
anterior and posterior cervical techniques. The posterior cervical technique involves
dural repair. The synthetic materials used for artificial dura can result in foreign-body
granuloma. Only one case report has been published so far involving the spine and
this included cervical spine.[2] There has been no other case report or series involving the spine till date. A series
of cases have been published regarding the same following craniectomy.[3] The objective of the study is to outline the characteristic features and the complication
of post-surgical granuloma in spine surgery in a patient with Hirayama disease.
Case Report
A 19-year-old young male presented with history of progressive weakness of bilateral
hands and associated reduced bilateral hand muscle bulk for 2 months. He complained
of difficulty in writing and using hand for daily routine activities. He was unable
to lift weights and had pain in bilateral hands. There was no history of trauma, spasticity,
or lower limb involvement. On examination, he had bilateral symmetrical wasting and
weakness of hand muscles flattened thenar and hypothenar eminences, involving right
more than left with right hand grip weakness of 60 percent. Reflexes and sensations
were normal. There was no other neurological deficit. In suspicion of Hirayama disease,
dynamic MRI cervical spine was advised, which revealed anterior displacement of posterior
dural with prominent posterior epidural fat on flexion from third cervical to first
thoracic (C3 to T1) vertebral level along with subtle spinal cord signal changes at
the C7–T1 level, confirming the same ([Fig. 1A]–[C]). He underwent C3–T1 laminectomy and bilateral lateral mass screw placement and
duroplasty with ReDura under intraoperative neurophysiological monitoring. Intraoperative
findings included epidural venous engorgement, thickened dura from C3 to C5 vertebrae.
The patient was stable during the discharge and was advised cervical collar ambulation
and limb physical therapy.
Fig. 1 Hirayama disease presurgical and post-surgical status. (A) Sagittal T2-weighted (wt) sequence of cervical spine in neutral position shows no
significant abnormality. (B) Sagittal T2 wt sequence of cervical spine in flexion shows anterior displacement
of the spinal cord with prominent posterior epidural flow voids (arrow). (C) Axial T2 wt sequence of cervical spine at the C7–T1 level reveals subtle hyperintense
signal changes in the anterior column on both sides (arrow). (D and E) Sagittal T2 wt sequence showing linear thick hypointensity at the operative site
over the ReDura compressing the spinal cord with signal changes at the T1–T2 level
(arrows). (F) Axial T2 wt sequence showing T2 hypointensity at the C7–T1 level with cord signal
changes (arrow).
After 6 months, the patient complained right anterior thigh sensory loss and numbness
for 1 month, and difficulty in walking for 1 week. On examination, power of all the
limbs was 5 out of 5, and sensation was reduced on right side below T10–L3 dermatomes.
Ankle clonus was positive on both sides with spasticity in bilateral lower limbs and
exaggerated bilateral knee jerks. Following this, MRI was advised, which revealed
heterogeneously thickened linear T2 hypointensity at the operative site, anterior
to the ReDura from C3 to T1 vertebral level with subtle spinal cord signal changes
([Fig. 1D]–[F]). There was also a T1–T2 disc bulge causing cord indentation and mild bilateral
neural foraminal narrowing. Surgery was indicated to relieve the mass effect on the
cord. T2 laminectomy was done along with excision of the granulation tissue over the
previous duroplasty site. ReDura was also removed along with the granulation tissue.
Duroplasty was done with fascia lata. Histopathology revealed exuberant granulomatous
reaction with retractile foreign bodies, as well as fibroblastic and histiocytic proliferation
([Fig. 2A]–[D]). Post-surgery, his sensory loss improved and maintained the power of all the limbs.
He was discharged in stable condition and has no complaints on follow-up. MRI was
advised three months after the discharge. It showed residual spinal cord signal changes
and no granuloma ([Fig 3A], [B]).
Fig. 2 (A and B) Intraoperative images showing granuloma (arrow) at the duroplasty site. (C and D) Microscopy showed mesh-like refractile foreign body, eliciting exuberant foreign-body
granulomatous reaction with fibroblasts and histiocytes (arrows).
Fig. 3 (A and B) Sagittal and axial T2 wt sequences showing release of cord compression following
removal of granuloma (arrows) with resolving cord edema at the T1–T2 level.
Discussion
Hirayama disease is a disorder of the lower motor neurons involving the distal upper
extremity muscles which gradually turn atrophic. This condition is seen commonly in
the younger males and may involve cervical or thoracic spine.[3] The most common site is at the C7–T1 level.
An insidious onset of upper limb weakness and wasting, commonly involving the ulnar
forearms and intrinsic muscles of the hand, is the most common presentation, although
occasionally proximal upper limb involvement has been reported. Patients may also
present with tremors.
There are several factors that contribute to the disease process, including asymmetrical
growth of the spinal canal and cord in puberty, anterior displacement of the spinal
cord reducing blood flow through the anterior spinal artery due to compression by
the posterior cervical vertebrae, engorged venous plexus in the posterior epidural
space, shortened cervical roots, or dynamic instabilities in patients with long necks.[4]
Electrophysiological findings in Hirayama disease include F wave with normal latency
but reduced frequency and conduction velocity. Changes in the somatosensory and motor-evoked
potentials have been documented.[5]
MRI is the modality of choice to confirm the disease by obtaining flexion and neutral
views. The forward displacement of the posterior dura is diagnostic of the disease.
Flattening of the spinal cord and an increase in the laminodural space are the characteristic
imaging findings, demonstrated on the flexion view.[6] Other features are straightening of the cervical spine, prominent posterior epidural
flow voids, and post-contrast crescent-shaped posterior enhancement during flexion.
The popular “snake eye appearance” on MRI spine indicates permanent disaster, and
is due to ischemia or necrosis of the anterior horn cells.[7] Thinning and flattening of the cord are also characteristic.
While cervical collars are the initial treatment for the condition and require a longer
period of treatment, surgery is recommended to stop disease progression, to decompress
the spine, and to correct the alignment of the cervical spine.
Anterior and posterior cervical surgeries are the two known approaches used in Hirayama
disease. Anterior cervical surgery includes anterior cervical discectomy and fusion
or corpectomy decompression and fusion. Posterior cervical surgery involves posterior
fusion/fixation of C1–C6/C7 vertebrae or laminectomy/laminoplasty with duroplasty.[8] Duroplasty is done to prevent the displacement of the spinal cord compressing against
the vertebral bodies anteriorly as the diseased patients may have ectatic dura with
loss of elasticity.[9] The synthetic dura is used in duroplasty to repair the dural defects. Many such
synthetic durae are available at present and may result in foreign-body reactions.
The contents of the duroplasty material used in our study contained poly-L-lactic
acid with a trade name of ReDura, which is used widely. It is manufactured based on
biomimetic electrospun technology and has hydrophobic surface property, preventing
cerebrospinal fluid (CSF) leakage.[10]
Extensive foreign-body reactions have been documented using ReDura in a case series
of post-decompressive craniectomy patients.[11] Initiation of inflammatory response by the giant cells results in granuloma formation.
Initially, there is acute inflammation by mast cells, followed by chronic inflammation
by mononuclear cells, limited to the foreign-body site resulting in foreign-body giant
cell formation, responsible for granuloma.[12] It appears T1 and T2 hypointense without diffusion restriction with intense homogeneous
enhancement. The granuloma formed over the duroplasty if extensive can sometimes appear
as a thick mass, resulting in the adjacent spinal cord being affected by the mass
effect. On histology, such foreign-body granuloma is seen as a background of dense
connective tissue with crystal-like/retractile structures surrounded by multinucleated
giant cells and lymphocytes.
Despite the fact that the granuloma formation helps prevent CSF leaks in dural repair
surgery, foreign-body granuloma may need to be treated surgically to combat any underlying
mass effect, particularly on the spinal cord.
Conclusion
Surgery is necessary in Hirayama disease to halt the disease progression. Posterior
cervical surgery accompanied with duroplasty to repair the dural defect may result
in exuberant granuloma formation due to the synthetic material used. MRI scan helps
diagnosing the condition. Awareness of the foreign-body reaction to duroplasty materials
is important and re-surgery may be necessary to reverse the mass effect.
