Atypical Optic Neuritis: The Potential Red Flags

Background: Many potential causes of optic nerve inflammation exist, including typical and atypical causes, which require different management strategies.Objective: The objective of this study is to identify red flags that help differentiate typical from atypical optic neuritis (ON).Materials and Methods: This prospective study included 66 patients (100 eyes) with immune-mediated ON from January 2016 to June 2019, carefully excluding the nonimmune causes. The clinico-radiological features, investigations, therapy, and outcome were analyzed.Results: We evaluated 33 cases each of typical and atypical ON. The typical group included 29 idiopathic ON and four associated with multiple sclerosis. Atypical ON included 19 neuromyelitis optica (NMO), seven MOG-associated ON (MOG-ON), and others due to Sjogren's syndrome, granulomatous polyangiitis, sarcoidosis, and IgG4 disease. Atypical ON occurred significantly and more frequently with extremes of ages (<10 or >70 years), bilateral simultaneous or severe vision loss with early disc pallor, multiple attacks, symptoms/neuro-imaging indicating non-MS disease e.g., long segment ON/myelitis, large confluent lesions, the involvement of optic tract, chiasma, area postrema or diencephalon, and (pachy) meningitis. Systemic involvement and poor outcomes despite steroids and second-line immunosuppression were observed more often in the atypical ON.Conclusions: The red flags indicating atypical ON are onset at extremes of age, multiple attacks, bilateral simultaneous or severe to very severe vision loss, early disc pallor, neurological symptoms, or imaging abnormalities suggesting non-MS disease, systemic involvement, and poor steroid responsiveness. The awareness might help the clinician promptly identify and escalate therapy to ensure a better outcome.