To report a case of optic neuritis difficult to differentiate from ischemic optic neuropathy and optic nerve glioma.

A 63-year-old male visited our clinic because of a sudden painless decrease in visual acuity in his right eye. He had a relative afferent pupillary defect and inferior altitudinal scotoma with disc pallor in his right eye. Ischemic optic neuropathy was suspected based on these clinical observations. However, a focal enhancing lesion was found in the intracranial portion of the right optic nerve on gadolinium-enhanced T1-weighted MRI. The radiologist's report revealed right intracranial optic glioma. Optic neurectomy was planned in accordance with the suspicion for optic glioma. However, a systemic mega-dose methylprednisolone therapy which is relatively less invasive was performed first based on the decision that optic neuritis should be distinguished from optic nerve glioma. The patient was hospitalized and 1 gram of methylprednisolone was injected intravenously daily for 3 days. The patient's visual acuity in the right eye improved from 0.1 before treatment to 0.3 after treatment. MRI scans at 8 months after steroid treatment showed disappearance of the previously enhanced lesion suspicious for optic glioma with developed atrophic change. The patient was finally diagnosed with optic neuritis based on these results.

Careful differential diagnoses and therapeutic approaches to possible diseases are necessary because optic neuritis can manifest as a variety of clinical entities and imaging findings.