Importance of MOG-IgG in longitudinally extensive optic neuritis (LEON): a case report

Case Presentation: A 29 years caucasian female patient presented with acute painless altitudinal visual impairment on the right eye presented at wake up. After 7 days of symptom onset , she developed the same presentation on the left eye, evolving with bilateral amaurosis shortly before being admitted in our emergency department. She denied any other symptoms. Past medical history was not significant. Neurological examination demonstrated amaurosis with bilaterally fixed and dilated pupils. Bilateral optic disc edema was noted on fundoscopy (figure 1). LCR was normal and negative for oligoclonal bands. MRI demonstrated extensive bilateral hyperintense sign on both optic nerves, including intra-orbital, intracanalicular and optic chiasm segments with correspondent enhancement on T1- weighted post gadolinium (figure 2A, 2B, 2C). AQP-4 was negative and Anti-Mog IgG was positive in quantitative evaluation, confirming the diagnosis of MOGAD. Patient received IV methylprednisolone and PLEX for 5 days each and returned 1 month later with normal pupillary light reflex and significantly improved vision acuity (20/25 bilateral). Discussion: In the present report, guided by the clinical findings, we were able to establish diagnosis of MOGAD according to the 2023 panel in the context of an MRI that was not typical for the disease in question. Even though there have been some reports of tumefactive lesions such as those presented in patients positive for Anti-Mog IgG, those reports are commonly associated with AQP-4 positivity and currently represents a minority of the described MRI patterns for the disease. Final Comments: Although MRI presentation was atypical for MOGAD, presentation of optic neuritis in a young female patient with no relevant past medical history should prompt investigation not only for Multiple Sclerosis and NMOSD, but for other demyelinating diseases, which includes dosage of Anti-MOG IgG.