Isolated Optic Neuritis as the Presenting Feature of Neurosarcoidosis: A Case Report and Diagnostic Approach.

We report a rare case of neurosarcoidosis presenting as isolated optic neuritis in a 43-year-old man with a history of obstructive sleep apnea and daily marijuana use. The patient experienced progressive, painless unilateral vision loss over six weeks, highlighting an atypical initial manifestation of this condition. Ophthalmologic examination revealed left optic disc swelling, afferent pupillary defect, and impaired color vision. MRI demonstrated left optic nerve enhancement, while chest imaging identified bilateral hilar lymphadenopathy with noncalcified nodules. Mediastinoscopic biopsy confirmed noncaseating granulomas, establishing a diagnosis of sarcoidosis. Treatment with high-dose corticosteroids followed by methotrexate resulted in improved visual acuity from counting fingers to 20/40, with resolution of optic nerve enhancement observed at one-year follow-up. This case underscores the critical role of early recognition and timely immunosuppressive therapy in preventing irreversible vision loss in neurosarcoidosis.