Acute Myelin Oligodendrocyte Glycoprotein-IgG Optic Neuritis without Optic Nerve Enhancement.

Introduction: Optic neuritis (ON) is a common neuro-ophthalmological condition and remains a significant indicator of inflammatory conditions affecting the central nervous system. Varying etiologies exist for ON including multiple sclerosis, NMOSD, and MOGAD. Differential diagnosis is achieved using both radiological and serological testing. MRI characteristics of MOG-ON include T2 hypersensitive lesions, nerve swelling, and gadolinium enhancement of the affected optic nerve. While acute MOG-ON usually presents with optic nerve enhancement, recognizing atypical presentations is critical in accurate diagnosis and effective management.

Case presentation: We herein present a case of a 67-year-old woman presenting with sudden decrease in vision in the right eye. The patient underwent a 3T MRI of the orbits and brain 5 days post vision loss which returned normal right optic nerve appearance at presentation (no edema, enhancement or increased T2 signal). Further serological testing of the MOG antibody returned positive (1:100) while APQ4 antibodies were negative. This yielded a diagnosis of MOG-IgG-ON. Subsequently, the patient was treated with IV methylprednisolone 1 g daily for 5 days followed by prednisone 1 mg/kg, resulting in marked improvement in vision.

Conclusion: This case highlights the complexity involved in diagnosing ON, especially in the context of MOGAD. Absence of optic nerve enhancement in this patient calls attention to the possibility of subclinical inflammation and/or detectable enhancement later in clinical course. Our findings, along with existing literature, highlight the need for clinicians to consider atypical MRI presentations in MOG-ON cases. Recognizing that normal MRI does not exclude MOG-ON is important for optimizing diagnostic accuracy and effective treatment interventions.