A 9-year-old girl presents with 5 days of progressive painful vision loss in the right eye following an upper respiratory infection. Examination reveals hand motions vision, a relative afferent pupillary defect, and red desaturation. Funduscopy shows the structure marked **A** — a markedly swollen, hyperemic optic disc with blurred margins and peripapillary hemorrhages. MRI brain and orbits with contrast shows optic nerve enhancement. Serum MOG-IgG is positive by cell-based assay. Which of the following best describes the PRIMARY PATHOPHYSIOLOGICAL MECHANISM underlying the optic disc swelling in this patient's condition?
A. IgG antibodies targeting aquaporin-4 water channels on astrocytic endfeet, leading to astrocytic loss and necrosis
B. Chronic demyelination from multiple sclerosis with preferential involvement of the optic nerve in pediatric patients
C. Oligoclonal bands in cerebrospinal fluid triggering demyelination restricted to the optic nerve sheath
D. IgG antibodies targeting myelin oligodendrocyte glycoprotein (MOG) on the outer surface of oligodendrocytes, causing demyelination and axonal inflammation
Explanation
Why option 1 is right
The swollen, hyperemic optic disc marked A in pediatric optic neuritis with MOG-IgG seropositivity reflects demyelination caused by IgG antibodies targeting myelin oligodendrocyte glycoprotein (MOG) on the outer surface of oligodendrocytes. This is the defining pathophysiology of MOGAD (MOG-antibody-associated disease), which accounts for ~50% of pediatric optic neuritis cases. The anterior papillitis presentation with prominent disc swelling is characteristic of MOGAD and differs from the retrobulbar form seen in adult MS-associated optic neuritis. The cell-based assay confirmation of serum MOG-IgG directly establishes this mechanism as the underlying etiology (Pediatric Neuro-Ophthalmology Society Guidelines; AAO BCSC Section 5).
Why each distractor is wrong
Option 2 (Aquaporin-4): While AQP4-IgG antibodies cause neuromyelitis optica spectrum disorder (NMOSD), this patient is MOG-IgG positive, not AQP4-IgG positive. NMOSD typically presents with worse visual outcomes and a more aggressive course than MOGAD.
Option 3 (Oligoclonal bands): Oligoclonal bands are characteristic of multiple sclerosis and are typically absent in the CSF of MOGAD patients. This patient's MOG-IgG positivity excludes MS-associated optic neuritis as the primary mechanism.
Option 4 (Multiple sclerosis): MS-associated optic neuritis is uncommon in young children and typically presents with the retrobulbar form rather than the prominent anterior papillitis seen here. The positive MOG-IgG serology and excellent prognosis (>80% recover to 20/40 or better) favor MOGAD over MS.
High-YieldNEET PG
Pediatric optic neuritis with anterior papillitis (swollen hyperemic disc) + MOG-IgG seropositivity = MOGAD; distinguish from AQP4-IgG (NMOSD) and oligoclonal bands (MS).
Pediatric Neuro-Ophthalmology Society Guidelines; AAO BCSC Section 5
Practice similar questions
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.
