Out of sight, hiding in plain clues.

A 76-year-old man with advanced non-small cell lung carcinoma undergoing treatment with carboplatin and paclitaxel plus pembrolizumab presented to the emergency department with a one-week history of rapidly progressive, severe bilateral visual loss and pain on eye movement. Ocular movements were full, with no other neurological deficits noted. Visual acuity was reduced bilaterally: 20/63 right eye, 20/200 left eye. Color vision testing was borderline normal, bilateral visual fields were constricted, while both funduscopy and optical coherence tomography were unremarkable. Urgent magnetic resonance imaging of the brain revealed patchy FLAIR hyperintensities in both optic nerves and faint post-contrast enhancement. By the time of neurological assessment one week later, the patient had experienced partial spontaneous improvement in vision. A comprehensive neuro-oncological differential diagnosis was performed, prompting the request for further diagnostic tests. This case illustrates the evolving landscape of neuro-oncology, where advances in diagnostic approaches and the use of immunotherapies such as pembrolizumab may alter immune tolerance, leading to immune-related adverse events such as myelin oligodendrocyte glycoporotein antibody-associated disease.