Primary Central Nervous System Lymphoma Presenting as Optic Nerve Infiltration: A Case Report.

Primary central nervous system lymphoma (PCNSL) is a rare type of non-Hodgkin lymphoma, which uncommonly presents with optic nerve infiltration (ONI). ONI has been reported mostly in relapse cases of PCNSL and is rarely the sole manifestation of the disease at the time of diagnosis. We report a case of a 69-year-old female who presented with progressive visual impairment with relative afferent pupillary defect (RAPD) on examination. Orbital and cranial magnetic resonance imaging (MRI) revealed bilateral optic nerve sheath contrast enhancement with an incidental finding of a right frontal lobe mass. Routine cerebrospinal fluid analysis and cytology were unremarkable. Excision biopsy of the frontal lobe mass yielded the diagnosis of a diffuse B-cell lymphoma. Intraocular lymphoma was excluded on ophthalmologic workup. Whole body positron emission tomography scan did not reveal extracranial involvement establishing the diagnosis of PCNSL. Chemotherapy was initiated with rituximab, methotrexate, procarbazine, and vincristine as induction regimen and cytarabine as consolidation therapy. On follow-up, the visual acuity of both eyes significantly improved with the resolution of RAPD. Repeat cranial MRI did not show a recurrence of the lymphomatous process. To the best of the authors' knowledge, ONI as the initial presentation at the time of PCNSL diagnosis has only been reported three times. The present case's unusual presentation highlights the need to consider PCNSL as a differential diagnosis in patients who present with visual deterioration and optic nerve involvement. Prompt evaluation and treatment of PCNSL are essential for improving the visual outcomes of patients.