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A 27-year-old woman presents to the neurology clinic with a 3-day history of painful loss of vision in the right eye, worse on eye movement. Three years ago she had an episode of numbness from the waist down that resolved spontaneously over 6 weeks. On examination: right visual acuity 6/60, reduced red desaturation, a right relative afferent pupillary defect (RAPD), a central scotoma, and a swollen right optic disc. Motor, reflex, plantar, sensory, and cerebellar examination of the limbs is normal.
Questions
a) What is the most likely diagnosis, and what is the unifying diagnostic principle? (2 marks)
Relapsing-remitting multiple sclerosis (MS). The unifying principle is dissemination in time and space — two CNS demyelinating events (optic neuritis now, a partial transverse myelitis three years ago) in different anatomical locations at different times.
b) List the four key clinical signs of optic neuritis demonstrated in this patient, and explain the mechanism of one. (3 marks)
- Painful unilateral visual loss (periocular pain on eye movement from inflamed optic-nerve dural sheath / extraocular muscle attachment).
- Relative afferent pupillary defect (RAPD) on the swinging-flashlight test — a lesion of the optic-nerve afferent limb.
- Reduced colour vision (red desaturation) — early dyschromatopsia.
- Central scotoma and disc swelling (papillitis).
Mechanism of RAPD: swinging the light to the affected eye delivers reduced afferent input (impaired optic nerve conduction); both pupils paradoxically dilate because the consensual response from the better-seeing eye is withdrawn.
c) Outline the investigations you would order to confirm the diagnosis and exclude mimics. (3 marks)
- MRI brain and whole spinal cord with gadolinium — looking for periventricular Dawson fingers, juxtacortical, infratentorial and short spinal-cord lesions, with gadolinium enhancement (dissemination in time).
- Lumbar puncture with paired serum — CSF oligoclonal bands present in CSF but not serum (intrathecal IgG synthesis); raised IgG index.
- Bloods to exclude mimics before any disease-modifying therapy: vitamin B12, ANA, ACE, AQP4-IgG (NMOSD), MOG-IgG (MOGAD), HIV, syphilis serology, TSH.
- Visual evoked potentials if historic optic-nerve involvement is in question (delayed P100).
d) State the acute treatment and the long-term management principles. (2 marks)
- Acute relapse: IV methylprednisolone 1000 mg daily for 3 to 5 days with gastroprotection; plasma exchange if steroid-refractory.
- Long-term: confirm AQP4 and MOG are negative, then start a disease-modifying therapy (e.g. interferon-beta, glatiramer, or escalation to an oral agent / monoclonal antibody by activity); arrange a multidisciplinary team (MS nurse, physiotherapy, occupational therapy), address symptomatic issues, advise smoking cessation and adequate vitamin D, and arrange annual MRI surveillance and specialist follow-up.