In a postpartum woman with acute visual loss and pain on eye movement, what is the most likely diagnosis and how should it be managed safely while breastfeeding?

Optic Neuritis in the Postpartum Period

In a postpartum woman presenting with acute visual loss and pain on eye movement, optic neuritis is the most likely diagnosis and should be treated immediately with high-dose intravenous methylprednisolone (1 gram daily for 3 days) followed by oral prednisone taper, which is safe during breastfeeding and does not require weaning. 1, 2

Clinical Presentation and Diagnosis

Optic neuritis in the postpartum period presents with:

• Sudden onset of unilateral visual impairment with pain on eye movements 3, 4, 2
• Relative afferent pupillary defect (Marcus-Gunn pupil) on examination 4, 2
• Decreased central visual acuity, impaired color vision, and visual field defects 4, 2
• Optic disc edema in approximately one-third of cases 2

The diagnosis is primarily clinical, based on the constellation of symptoms and examination findings. 2

Critical Diagnostic Workup

MRI imaging is essential and should include:

• MRI of the head and orbits with and without IV contrast to identify abnormal optic nerve enhancement (detected in 95% of optic neuritis cases) and evaluate for demyelinating lesions elsewhere in the brain 5
• T1-weighted post-contrast images with fat suppression are the most sensitive sequences for detecting optic nerve inflammation 5

This imaging serves two critical purposes:

• Confirms the diagnosis of optic neuritis 5
• Assesses risk for multiple sclerosis, as optic neuritis is often the first manifestation of MS 3, 4, 2

Treatment Protocol

Immediate treatment with high-dose intravenous corticosteroids is indicated:

• Methylprednisolone 1 gram IV daily for 3 days, followed by oral prednisone taper over 11 days 1, 2
• This regimen accelerates visual recovery, though it does not improve final visual outcome 2
• Visual function recovers spontaneously in 95% of cases, but treatment speeds this recovery 2

Safety During Breastfeeding

Corticosteroid treatment is compatible with continued breastfeeding:

• Systemically administered corticosteroids do appear in human milk, but the decision to continue nursing should weigh the importance of the drug to the mother against potential infant effects 6
• In the case series of four lactating mothers with optic neuritis, all were successfully treated with IV steroids followed by oral steroids with complete visual recovery 1
• Breastfeeding does not need to be discontinued for standard optic neuritis treatment 1

Weaning is only necessary if:

• MRI reveals extensive demyelinating disease requiring long-term immunosuppressive therapy beyond acute corticosteroid treatment 1
• Two of four patients in the case series required weaning specifically because they needed ongoing immunosuppressive therapy for multiple sclerosis, not because of the acute steroid treatment 1

Important Clinical Pitfalls

Do not delay treatment while awaiting MRI results - the clinical diagnosis is sufficient to initiate therapy, and treatment speeds recovery 1, 2

Do not assume lactation itself causes the optic neuritis - postpartum optic neuritis represents immune-mediated demyelinating disease, often as the first manifestation of multiple sclerosis 3, 7

Do not use oral corticosteroids alone as initial therapy - high-dose IV methylprednisolone is the standard of care based on the Optic Neuritis Treatment Trial 1, 2

Recognize atypical features that suggest alternative diagnoses:

• Bilateral simultaneous involvement may indicate neuromyelitis optica spectrum disorder 5
• Lack of pain or poor visual recovery may suggest neuromyelitis optica 2
• Macular involvement suggests neuroretinitis rather than typical optic neuritis 2

Long-term Considerations

MRI findings determine multiple sclerosis risk and need for disease-modifying therapy:

• Patients with brain lesions on MRI are at high risk for developing MS 2
• Beta-interferon or glatiramer acetate prophylaxis is recommended for high-risk patients 2
• MRI of the complete spine may help differentiate between MS and neuromyelitis optica spectrum disorders if demyelinating lesions are present 5

Follow-up ophthalmologic examination is essential to document visual recovery and monitor for recurrence 1, 4