Acute Loss of Vision
Try out this example neurology case and test your clinical knowledge. The answers are at the bottom.
A 34-year-old woman presents to A&E with pain in her left eye. She reports that the pain began half an hour ago and is around 7/10 in intensity. On further questioning she mentions that the pain is worse when she looks from side to side and that she had trouble judging how far away cars were from her on the drive over.
– Difficulty seeing red dots on Ichihara plates, no evidence of colour blindness
– Visual acuity 8/20 on L side (previously 20/20), 20/20 in R side
– On right lateral gaze L eye remains central, R eye displays torsional nystagmus
– Swinging light test:
–> When light is shone in R eye, both pupils constrict
–> When light is shone in L eye, both pupils dilate
Upper & Lower Limb Neuro:
– Power 5/5
– Normal reflexes and tone
– No sensory deficits
Non-contrast CT Head:
Fundoscopy of left eye:
Image 1: University of Iowa Healthcare: https://bityl.co/6Ene
Q1: Comment on her examination findings and the appearance of the fundus – how does this fit in with her clinical picture?
Her symptoms resolve in the emergency department and the registrar discharges her with some ibuprofen.
Two months later she re-presents to A&E with persistent weakness in her right arm. Examination reveals a positive Hoffmann’s reflex. An initial non-contrast CT head is unremarkable. The registrar orders an urgent MRI of the CNS.
Q2: What other specific investigations would support the likely diagnosis?
Case Continued: The MRI results are shown below:
Axial MRI Brain:
– Hypointense lesions in the pre-chiasmatic left optic nerve and left MLF
Image 2: Case courtesy of Assoc Prof Frank Gaillard, Radiopaedia.org, rID: 35916:
Q3: Comment on all the MRI findings. What is the diagnosis?
Q4 (Bonus!): Why could this diagnosis not have been made at her initial presentation?
Reveal the answers
Key points to include:
- Normal observations – no features of infection e.g. orbital cellulitis
- Pain on eye movements is pathognomic for optic neuritis (inflammation of the optic nerve)
- Difficulty judging depth – Pulfirch effect
- Difficulty seeing red – red desaturation
- Loss of visual acuity in affected eye – likely damage to retina or optic nerve (unilateral loss of vision means that the pathology is likely pre-chiasmatic i.e., early optic nerve or retina)
- Swinging light test demonstrates a RAPD on the left – this isolates the pathology to the optic nerve (but it does not rule out other pathologies e.g., temporal arteritis can cause RAPDs due to ischemia of the head of the optic nerve)
- Fundoscopy is normal! The damage here is in the portion of the nerve behind the optic bulb i.e., retrobulbar optic neuritis, so it cannot be seen by fundoscopy (requires MRI of the orbits). This differentiates it from conditions like temporal arteritis which cause an anterior (ischaemic) optic neuropathy and would present with a pale & swollen optic disc on fundoscopy
- Eye movement test reveals a specific form of visual field defect known as intranuclear ophthalmoplegia (INO) – indicates damage to the medial longitudinal fasciculus (MLF) on the L side
- Normal UL/LL neuro exams – likely no pathology in the spinal cord or motor/sensory cortices
- Normal CT head – no evidence of acute strokes or bleeds
- Other features you may expect – Uhthoff’s phenomenon (symptoms worsen as body temperature rises)
Working diagnosis of demyelinating disease:
– Lumbar puncture:
– Unpaired oligoclonal bands in CSF – would support a diagnosis of MS
– Myelin basic protein – would support a diagnosis of MS
– IgG – raised immunoglobulins in MS
– Lack of anti-Aquaporin-4 antibodies (exclude neuromyelitis optica, an MS mimic)
– Lack of oligoclonal bands in blood (unpaired – present only in CSF in MS)
Ultimately the gold standard investigation is an MRI brain + spine with contrast
Normal MRI spine effectively excludes neuromyelitis optica
– Classically only affects the optic nerve and spinal cord (transverse myelitis)
Axial MRI Brain:
– Low intensity lesion in L optic nerve and L MLF – these are old lesions (the optic neuritis & INO from her first presentation)
Sagittal MRI brain:
– This is a FLAIR MRI (FLAIR = T2 with the CSF signal attenuated) – the best sequence for detecting demyelinating plaques
– Hyperintensities spreading vertically from the corpus callosum – these are acute lesions known as Dawson’s fingers
– Periventricular plaques
Diagnosis: Multiple Sclerosis
MS is diagnosed using the revised McDonald criteria, which requires dissemination in time AND in space (i.e., two or more attacks separated in time in two or more locations). This has been fulfilled at her second presentation (two lesions in different places two months apart).
At her initial presentation, she had only had one attack (likely with two lesions disseminated in space – the left MLF and left optic nerve) but no further investigations were undertaken to check for previous silent episodes, as such there was no dissemination in time. Of interest, the presence of oligoclonal bands can be used as a marker of dissemination in time as it suggests previous disease activity – a good summary is presented here https://mstrust.org.uk/a-z/mcdonald-criteria
To get more information about the conditions mentioned in this case including diagnosis and management, have a look at our free neurology notes on In2Med. Written by medical students, we have pitched them just at the right level to help you ace your exams.
Dr Amol Joshi
University of Cambridge