Diagnostic Approach to Optic Neuritis

Primary Demyelinating Disorders

• The presence of even one clinically silent T2 hyperintense brain lesion on MRI is highly associated with eventual MS diagnosis, with hazard ratios of 5.1 for 1-3 lesions and 11.3 for ≥10 lesions, according to the American Academy of Neurology 1.
• CSF oligoclonal bands combined with brain MRI lesions dramatically reduce the likelihood of monophasic illness, as recommended by the American Academy of Neurology 1.

Vascular Causes

• Multifocal areas of cerebral ischemia or infarction in young adults can mimic MS and should be considered, particularly from phospholipid antibody syndrome, acute disseminated lupus erythematosus, CADASIL, Takayasu's disease, meningovascular syphilis, or carotid dissection, as suggested by the American Heart Association 2, 3.

Infectious Etiologies

• HTLV1 and Lyme disease can present striking similarities to MS and must be excluded, as recommended by the Infectious Diseases Society of America 2, 3.

Inflammatory and Autoimmune Disorders

• SLE can cause inflammatory optic neuritis with poor visual outcomes, with only 30% maintaining visual acuity >20/25, according to the American College of Rheumatology 1.
• Treatment delay beyond 2 weeks is an unfavorable prognostic factor, particularly in SLE-related cases, as recommended by the American College of Rheumatology 1.

Monophasic Demyelinating Diseases

• A diagnosis of ADEM should not be made unless new symptoms and signs or imaging abnormalities appear more than three months after clinical onset, as suggested by the American Academy of Neurology 2, 3.

Diagnostic Algorithm

• MRI of orbits and brain with contrast is the primary diagnostic study, serving to evaluate for abnormal enhancement and T2 signal changes within the optic nerve, as well as to assess for intracranial demyelinating lesions predicting MS risk, according to the American Academy of Neurology 1.
• Immediate testing for AQP4-IgG and MOG-IgG is mandatory in any atypical presentation, as recommended by the American Academy of Neurology 1.

Additional Workup Based on Clinical Context

• CSF analysis for oligoclonal bands when MS risk stratification is needed, as recommended by the American Academy of Neurology 1.
• Infectious workup including Lyme serology, HTLV1, syphilis testing based on exposure history, as suggested by the Infectious Diseases Society of America 2, 3.
• Autoimmune panel including ANA, anti-dsDNA for SLE consideration, as recommended by the American College of Rheumatology 1.