Optic chiasm, optic tract and deep white demyelination: an unusual distribution of myelin oligodendrocyte glycoprotein-associated demyelination (MOGAD), case report and review of literature
- 1 Fellow LVPEI, Standard Chartered LVPEI Academy of Eye Care Education, LV Prasad Eye Institute, Hyderabad, Telangana, India
- 2 Child Sight Institute, Jasti V Ramanamma Children's Eye Care Centre, LV Prasad Eye Institute, Hyderabad, Telangana, India
- 3 Paediatric Ophthalmology, Strabismus and Neuro-ophthalmology, LV Prasad Eye Institute, Visakhapatnam, Andhra Pradesh, India
- Correspondence to Dr Goura Chattannavar, Strabismus, Pediatric and Neuro-ophthalmology, LV Prasad Eye Institute, Hyderabad, Telangana, India; drgourachattannavar@lvpei.org
Abstract
A preschool girl presented with sudden-onset bilateral painless loss of vision from 2 days prior. Child’s examination showed light perception vision, sluggishly reacting pupils, otherwise normal anterior segment, healthy optic disc and retina in both eyes. MRI of brain and orbit with contrast revealed thickened left part of the optic chiasm with contrast enhancement extending proximally to bilateral optic tract and hyperintensities in the left thalamus and periventricular white mater. Considering the topographical distribution of lesions in the brain, neuromyelitis optica spectrum disorder was suspected. The child was started on intravenous methylprednisolone followed by tapering oral steroids. Serological testing was positive for myelin oligodendrocyte glycoprotein (MOG) and negative for aquaporin-4 antibodies. This case represents an unusual case of MOG associated demyelination disorder where the distribution of lesions showed chiasmal involvement along with optic tract, thalamus and deep white mater lesions.
Background
Optic neuritis is one of the common neuro-ophthalmological problems observed in the children. Although it can frequently be postinfectious, postvaccination or clinically isolated syndrome, recent studies have reported that nearly half of the patients might have an underlying neuroinflammatory disorder (myelin oligodendrocyte glycoprotein-associated demyelination (MOGAD) 18%, acute demyelination encephalomyelitis (ADEM) 16%, Multiple Sclerosis (MS) 11% and neuromyelitis optica spectrum disorder (NMOSD) in 7%.1 Thus MOGAD is increasingly being recognised as the most frequent cause of optic neuritis in children. As each underlying aetiology has differences in visual outcomes and chances of recurrences, therefore, it is important to distinguish between each syndrome to avoid future morbidity.2–4 Further studies have suggested specific differences in the characteristics of each neuroinflammatory syndrome based on age at presentation, laterality, associated clinical syndromes and distribution of MRI lesions.4 5 Although adult and paediatric optic neuritis are similar there are a few reported differences such as bilateral involvement with disc oedema, with no associated orbital pain, profound vision loss with good visual recovery seen in children.6 7
Contrast-enhanced MRI of brain, orbit and spine gives a diagnostic clue to the underlying aetiology owing to the characteristic differences in the distribution and characteristics involvement of lesions.5 8
However, definite diagnosis is by serological testing for glial proteins such as aquaporin-4, MOG, glial fibrillar acid protein and cerebrospinal fluid analysis to give the absolute etiological diagnosis and avoid surprises.1–5 This case highlights an unusual and challenging case where neuroimaging was more suggestive of NMOSD; however, the serological diagnosis confirmed a final diagnosis of MOGAD.
Case presentation
A preschool girl born to nonconsanguineous parents, presented to our neuro-ophthalmology department with complaints of bilateral sudden painless vision loss from 2 days prior. Her history was significant for enteric fever 3 months ago. There was no history of pain on eye movements, or any neurological complaints, and no prior history of recent vaccination.
The child did not have headache, vomiting, bladder incontinence, weakness in upper and lower limbs or seizures.
At presentation, her vision was light perception in both eyes. Anterior segment examination was unremarkable in both eyes, except for the sluggishly reacting pupil bilaterally. The fundus examination revealed healthy disc bilaterally (figure 1). Formal visual fields were not possible given poor vision and child’s age.
(A, B) Colour and (C, D) red free optic disc photograph of right and left eye respectively at presentation with bilaterally healthy optic disc.
Considering patient history, profound vision loss and examination findings, we suspected the child to have bilateral atypical optic neuritis. We advised the child to undergo MRI of brain and orbit with contrast and MRI whole spine screening was obtained.
Investigations
T1W-fat saturated images revealed normal calibre of bilateral optic nerves with thickened left part of chiasma which enhanced strongly with gadolinium contrast (figure 2). The enhancement was noted to extend proximally to bilateral optic tracts, (left more than the right). Additionally, MRI brain showed hyperintensities in the left thalamus and in the bilateral periventricular white mater in the occipital horn. Brain stem and spinal imaging was normal (figure 3). Given the topographical pattern of involvement (optic chiasm, optic tracts and deep brain) on MRI brain, the diagnosis of bilateral atypical optic neuritis secondary to NMOSD was strongly suspected. Serological testing for aquaporin-4 and MOG antibodies was advised.
(A–C) T2weighted fat-saturated coronal MRI of brain and orbit showing thickened left optic nerve in the proximal section (yellow circle). (D–F) Coronal and (G–I) axial section of orbit and brain with postgadolinium contrast depicting normal calibre of bilateral optic nerves with thickened left of chiasma (yellow arrow) and bilateral optic tract (dashed arrow) with contrast enhancement.
(A) T2 weighted fluid attenuated inversion recovery MRI brain showing hyperintensities in the left thalamus and in the right periventricular white mater in the occipital horn, (B) hyperintensity in the left periventricular white mater in the occipital horn, (C) brain stem and spinal MRI showing no hyperintensities.
Differential diagnosis
A provisional diagnosis of atypical optic neuritis possibly secondary to a neuroinflammatory syndrome was strongly considered. With the topographical distribution of lesions, neuromyelitis optica was on the higher suspicion, followed by MOGAD.
Treatment
The child was started on intravenous methyl prednisone 30 mg/kg/body weight per day for 5 days, followed by oral tapering along with oral calcium supplements and a paediatric neurologist opinion was sought.
The child was advised by the paediatric neurologist to continue tablet prednisolone 10 mg per day for next 3 months to decrease the chances of recurrence which is reported to be high in MOG associated optic neuropathy.9
Outcome and follow-up
To our surprise, serology revealed aquaporin-4 antibody was negative but positive for MOG antibody.
At 2 weeks follow-up, child’s vision had improved to 20/60 and 20/80 in the right eye and left eye, respectively. Oral steroids were slowly tapered over 3 months period and at the final follow-up; her best corrected visual acuity (BCVA) was 20/30 in both eyes. Fundus examination revealed temporal pallor in BE (figure 4A,B). Visual field analysis using Humphrey visual field perimeter, although with low test reliability showed central scotoma in BE (figure 4E,F). Repeat neuroimaging at 3 months follow-up showed interval resolution of the intracranial lesions (figure 4G–I).
Final outcome and follow-up images at 3 months from presentation (A, B) colour optic-disc photograph, (C, D) red free fundus photograph revealing both eye temporal pallor, (E, F) showing Humphrey visual fields depicting centrocaecal scotoma in both eyes, (G–I) depicts T2 weighted MRI after 3 months which showing resolution of chiasmal and brain hyperintensities.
Discussion
Optic neuritis is an acute inflammatory condition causing painful vision loss, dyschromatopsia and visual field defects. It is relatively uncommon in children and varies from 0.15 to 4.4/100.00 person-years in various ethnicities.7 10
As noted above, prospective longitudinal studies suggest 50% of children with paediatric optic neuritis can have an underlying neuroinflammatory syndrome, with MOGAD accounting for majority of them.1 3 4 This case represents a challenging situation with atypical neuroimaging findings likely suggestive of NMOSD, but serological findings confirming MOGAD.
In this case, the child presented with bilateral acute profound painless vision loss, with good visual recovery at the end of 3 months after initiating the treatment. This presentation is similar to the clinical profile described in literature for paediatric optic neuritis. 6 8However, our patient had bilateral normal fundus, unlike existing reports that suggest the children usually have papillitis.1 11 Prodromal symptoms or post vaccination may precede the onset of paediatric optic neuritis. Nevertheless, there are clinical evidence of its association with neuroinflammatory syndromes which includes multiple sclerosis (MS), ADEM, NMOSD or MOG-associated optic neuritis.2 In literature, optic neuritis post enteric typhoid fever is reported as one of the rare ocular associations.12–14 The exact mechanism is not yet understood but possible mechanisms described are likely due to meningitis or immune mediated.15 16 Our patient had enteric fever (typhoid) 3 months ago which possibly may or may not be related to this episode of demyelinating optic neuropathy.
The characteristic and location of lesions on neuroimaging gives a clue to underlying aetiology of neuroinflammatory syndromes.5 8 In MS-associated optic neuritis, there is involvement of unilateral short segment of the optic nerve, white matter tracts in brain and short segment involvement in spinal cord.5 Studies have reported clues to differentiate NMOSD associated optic neuritis from MOG associated radiographically.5 8 Both NMO-associated and MOG-associated optic neuritis show unilateral or bilateral long segment involvement of optic nerve. While optic neuritis in MOGAD can involve long segments (more than 50% of the length) of the intracranial optic nerve but often spares the optic chiasm, optic neuritis in NMOSD may involve proximal optic nerve, intracranial optic nerve as well as optic chiasm.17
Brain lesions are found in the periependymal or deep white matter areas mainly located in the area postrema (dorsal brainstem and hypothalamus) with large spinal cord lesions involving greater than three non-contiguous segments of both white and grey matter in NMOSD. In MOG, although the lesions are found in the periependymal or deep white matter areas, they are larger and widespread in the entire white matter and mainly located in the cerebral penduncles with a acute disseminated encephalomyelitis (ADEM) like pattern. Involvement of thalamus and pons are reported to be specific to MOG optic neuritis while medulla oblongata and area postrema are more commonly involved in NMOSD.18
Spinal cord lesions mostly involve the cervical or thoracic spine in NMO optic neuritis and lumbo-sacral segments in MOG optic neuritis. In our patient MRI showed involvement of optic chiasm and optic tract with hyperintensities and periventricular white matter of occipital horn that raised suspicion of NMOSD.5 8 19
However, our patient aquaporin antibody was negative; rather patients’ MOG antibodies were positive.
According to prior literature, chiasmal and optic tract involvement is rarely seen in MOG-AD optic neuritis.5 8 20 Ramanathan et al in his study on radiological differences in MOG, NMO, MS reported 5% of chiasmal involvement in MOG, 64% in NMO and 15% in MS.20 Similarly, Chen et al reported chiasmal involvement in 12% children with MOG and Zhao et al reported 15% MOG ON with involvement of optic chiasm.9 21
Unlike NMOSD which has poor outcomes and severe damage occurs following each episode, MOG patients usually have better visual recovery but might still be associated with recurrences. MOG-IgG is more commonly seen in childhood demyelinating attacks and has a monophasic course in 70%.4 6 Therefore, it is important to distinguish between the two. This case highlights the role of recognising uncommon presentation of optic chiasm and deep white mater involvement in patients with MOG optic neuritis.
Given widespread demyelination in the brain, young age at presentation, paediatric neurologist consult was taken, and long-term immunosuppression planned to prevent recurrences.
Patient’s perspective
After a cheerful day at play and family night meals my child went to sleep. The next day she complained of not able to see anything. We repeatedly asked her the same and she constantly said she couldn’t see. We were shocked and went to a local eye hospital. They referred her to a tertiary care centre where we rushed her to emergency. Here they performed a couple of tests and started her on intravenous Methylprednisolone for 5 days and continued with oral steroids. Following the treatment my child’s vision improved to more than 50%. We consider ourselves fortunate and are grateful to the doctors and hospital staff for their timely intervention. My child is now able to see and play with her friends as well.
Learning points
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Our case highlights the rare occurrence of involvement of segment of optic chiasma and optic tract in myelin oligodendrocyte glycoprotein-associated optic neuritis.
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It is essential to know the radiological and serological diagnosis which gives us a proposition of the duration and choice of treatment, the probability of relapse and visual prognosis.
Ethics statements
Patient consent for publication
Footnotes
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Contributors AL: manuscript writing, editing GC: Idea of report, manuscript writing, editing, revising VS: supervision and revision. RK: Supervision and revision.
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Funding This study was funded by Hyderabad Eye Research Foundation (LEC-BHR-R-06-22-909).
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Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.
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Competing interests None declared.
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Provenance and peer review Not commissioned; externally peer reviewed.
- © BMJ Publishing Group Limited 2022. No commercial re-use. See rights and permissions. Published by BMJ.
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