Overview
This lecture covers optic neuritis, focusing on its types, pathophysiology, clinical features, associations, diagnosis, and distinction between typical and atypical cases, especially regarding multiple sclerosis and related conditions.
Definition and Types of Optic Neuritis
- Optic neuritis is a demyelinating inflammation of the optic nerve.
- Types based on location: papillitis (optic disc), retrobulbar neuritis (intraorbital nerve), and neuroretinitis (disc + retina).
- Demyelination is the core feature; inflammation may also involve autoimmune and infectious processes.
Pathophysiology
- Demyelination is triggered by blood-brain barrier breakdown, allowing immune cells into neural tissue.
- Autoimmunity leads to T cells attacking oligodendrocytes and myelin.
- Inflammation causes further nerve damage and edema.
- Histologically, perivascular cuffing (T, B, plasma cells) and myelin breakdown are observed.
Associations
- Optic neuritis may be isolated, or associated with multiple sclerosis (MS), neuromyelitis optica (NMO), or acute disseminated encephalomyelitis (ADEM).
- New antibodies: AQP4-IgG (aquaporin 4, associated with NMO) and MOG-IgG (myelin oligodendrocyte glycoprotein, associated with MOG-ON).
- Infectious (viral, bacterial, fungal, protozoal, parasitic) and autoimmune (e.g., SLE, polyarteritis nodosa) causes exist.
Clinical Features
- Rapidly progressive, mostly unilateral vision loss (hours to 1 week), often with pain on eye movement (ages 18–45).
- Red color desaturation and altered motion perception (Pulfrich phenomenon) occur.
- Symptoms may worsen with heat/exercise (Uhthoff’s sign).
- Visual recovery starts by week 2–3 and returns near normal in weeks 4–5, but color vision and contrast may take 6–12 months.
- Recurrences, bilateral involvement, or deviation from typical course suggest atypical optic neuritis.
Diagnosis and Investigations
- Visual loss, decreased color vision, RAPD (Marcus Gunn pupil), delayed VEP (P100 latency).
- Fundus exam: normal disc in retrobulbar neuritis; disc edema in papillitis; macular exudates in neuroretinitis.
- MRI brain/orbit: short segment nerve enhancement (typical ON/MS); long segment/intracranial or bilateral (NMO/MOG).
- MS risk: higher in young women, Caucasians, northern latitude, with specific MRI findings.
- MS diagnosis (McDonald criteria): dissemination in space (≥1 T2 lesion in ≥2/4 CNS areas) and time (new vs old lesions).
- Oligoclonal bands/IgG in CSF support MS but less predictive than MRI.
- NMO diagnosis: optic neuritis + acute myelitis with AQP4 antibody, ≥3 spinal segments, and atypical brain MRI.
Typical vs Atypical Optic Neuritis
- Typical: age 18–45, mild pain, unilateral, short segment MRI lesions, fast recovery, no recurrence after steroids.
- Atypical: outside age range, severe/no pain, bilateral, poor vision >2 weeks, severe edema/hemorrhages, recurrent/worsened with steroids, long segment or chiasmal MRI lesions.
Key Terms & Definitions
- Optic neuritis — Inflammatory demyelination of the optic nerve.
- Demyelination — Loss of myelin sheath insulating nerve fibers.
- Papillitis — Optic disc inflammation.
- Retrobulbar neuritis — Inflammation of the intraorbital optic nerve.
- Neuroretinitis — Inflammation of optic nerve and retina.
- AQP4-IgG antibody — Antibody against aquaporin-4, linked to NMO.
- MOG-IgG antibody — Antibody against myelin oligodendrocyte glycoprotein.
- Multiple sclerosis (MS) — Chronic CNS demyelinating disease.
- NMO (Devic’s disease) — Optic neuritis plus transverse myelitis.
- Pulfrich phenomenon — Altered perception of moving objects due to conduction velocity disparity.
- Uhthoff’s sign — Worsening of vision with increased body temperature.
- Relative afferent pupillary defect (RAPD) — Abnormal pupil response indicating optic nerve disease.
Action Items / Next Steps
- Review next lecture on treatment of typical and atypical optic neuritis.
- Memorize MS diagnostic criteria and differences between typical/atypical ON.
- Familiarize with key antibodies (AQP4, MOG) and related syndromes.
- Prepare for fundus findings and MRI patterns in different types of optic neuritis.