What is optic neuritis?

Optic Neuritis: Definition, Diagnosis, and Management

Optic neuritis is an acute inflammatory condition of the optic nerve, often presenting with painful visual loss, which can be unilateral or bilateral and frequently serves as the initial manifestation of multiple sclerosis. 1

Clinical Presentation

The classic triad of optic neuritis includes:

• Visual loss (typically subacute)
• Periocular pain (especially with eye movement)
• Dyschromatopsia (color vision abnormalities) 2

Additional clinical features:

• Typically affects young adults, with higher prevalence in women
• Higher incidence in populations living at higher latitudes
• Weaker direct pupillary light reflex in the affected eye in unilateral cases
• Optic disc edema (papillitis) in approximately one-third of cases 2, 3

Diagnostic Evaluation

Imaging

• MRI of the orbits and brain with and without contrast is the primary imaging study for initial assessment 1
• Serves two key purposes:
  1. Evaluating for abnormal enhancement and signal changes within the optic nerve (detected in 60-70% of cases)
  2. Assessing the brain for associated intracranial demyelinating lesions, which strongly predict subsequent development of multiple sclerosis 1, 4

Typical MRI findings:

• Acute lesions: T2 hyperintensity, optic nerve swelling, and contrast enhancement
• Post-acute/chronic lesions: Atrophy and T2 hyperintensity 1

Technical specifications for optimal imaging:

• High in-plane resolution (ideally 0.5 mm × 0.5 mm or better)
• Slice thickness of 3-4 mm
• Fat-suppressed sequences (2D coronal STIR, 2D coronal fast spin-echo) 1

Additional Testing

• Visual evoked potential tests can detect bilateral damage to the optic nerve before clinical manifestation 4
• Blood tests including inflammatory markers (ESR, CRP) and specific antibodies (AQP4-IgG and MOG-IgG) help identify conditions like neuromyelitis optica spectrum disorders 4

Differential Diagnosis

Optic neuritis must be distinguished from:

1. Multiple sclerosis-associated optic neuritis
2. Neuromyelitis optica (NMO) and NMO spectrum disorders
3. Anterior ischemic optic neuropathy (AION)
4. Leber's hereditary optic neuropathy
5. Infectious or granulomatous conditions 4, 2

Red flags suggesting alternative diagnoses:

• Posterior optic nerve involvement including the chiasm (suggestive of anti-AQP4-IgG-seropositive neuromyelitis optica)
• Simultaneous bilateral optic nerve involvement
• Long optic nerve lesions (suggestive of neuromyelitis optica spectrum disorders and anti-MOG-IgG disease)
• Perioptic nerve sheath enhancement or soft tissue enhancement extrinsic to the nerve 1

Treatment

Acute Management

• High-dose intravenous methylprednisolone (1g/day for 3-5 days), followed by oral prednisone in tapering doses is the standard treatment for acute optic neuritis 4, 5
• This treatment accelerates visual recovery but does not affect the final visual outcome 5, 3
• Oral prednisolone alone is contraindicated due to increased risk of a second episode 4

Long-term Management

• For patients at high risk of developing multiple sclerosis, immunomodulatory therapies such as interferon β-1a,b may reduce the risk of MS progression 2
• Studies including CHAMPS, BENEFIT, and ETOMS have demonstrated that these treatments reduce the risk of MS and influence MRI characteristics of optic neuritis 2

Prognosis

• Visual function recovers in approximately 95% of cases 3
• Despite good recovery of visual acuity, contrast sensitivity, color vision, and visual field often remain impaired 2
• Poor prognostic factors include:
  • Delayed treatment initiation
  • Extensive lesions on MRI
  • Presence of antiphospholipid antibodies 4

Special Considerations

Atypical Optic Neuritis

• May be associated with neuromyelitis optica spectrum disease (NMOSD), myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD), chronic relapsing inflammatory optic neuritis (CRION), and systemic autoimmune diseases 6
• Requires thorough investigation to determine underlying cause and guide appropriate treatment

Optic Neuritis in Systemic Conditions

• Optic neuritis associated with systemic lupus erythematosus has a poor visual prognosis, with only 30% maintaining visual acuity >20/25 4
• More aggressive immunosuppression may be considered in these cases
• Cyclophosphamide has shown superior response rates compared to methylprednisolone alone for severe, refractory neuropsychiatric lupus with optic neuritis 4

Clinical Pitfalls to Avoid

1. Misdiagnosing optic neuritis as other conditions like anterior ischemic optic neuropathy or Leber's disease
2. Using oral prednisolone alone, which increases the risk of recurrence
3. Failing to obtain appropriate MRI studies that could identify patients at high risk for MS
4. Not recognizing atypical features that suggest alternative diagnoses requiring different treatment approaches
5. Overlooking the need for long-term immunomodulatory therapy in patients at high risk for MS