Isolated optic neuritis after pembrolizumab administration for non-small-cell lung carcinoma

Purpose To report a case of isolated optic neuritis associated with pembrolizumab immunotherapy for metastatic non-small cell lung carcinoma. Case presentation A 76-year-old man, with a history of metastatic non-small cell lung carcinoma, presented with vision loss in his left eye for the past week. He had been treated with pembrolizumab for the underlying disease for 2 months. On presentation, best corrected visual acuity was 20/30 in the right eye and 20/200 in the left eye. Fundoscopy revealed optic nerve edema in the left eye. Visual fields examination in right eye revealed an enlarged blind spot and an extended defect in the inferior nasal quadrant. In the left eye a partial superior arcuate defect and an extended defect in the inferior hemisphere was observed. The mean deviation was -12.15 dB in the right eye and -13.70 dB in left eye. Pembrolizumab was withheld and corticosteroids were administered for a total of nine weeks, first intravenously and then slowly tapered orally, resulting in resolution of optic neuritis, restoration of visual acuity and in relative improvement in the visual field defects after 3 months. Calculated Naranjo Nomogram score was 7, indicating a 'highly probable' correlation. Conclusions Optic neuritis is a relatively rare immune-related adverse event after exposure to checkpoint inhibitors cancer immunotherapy. Prompt discontinuation of the offending agent and early initiation of corticosteroid therapy is the mainstay of the treatment.