Isolated Infiltrative Optic Neuropathy in an Acute Lymphoblastic Leukemia Relapse.

Optic nerve infiltration as the first sign of isolated central nervous system relapse of acute lymphoblastic leukemia (ALL) is rare. A seven-year-old girl with standard-risk B-cell ALL who was in remission presented with sudden onset of left eye pain and loss of vision. Examination revealed no perception to light in the left eye with positive relative afferent pupillary defect. The optic disc was hyperemic and swollen with total obscuration of the disc margin associated with central retinal artery and vein occlusion. Magnetic resonance imaging of the brain and optic nerve showed left intraorbital optic nerve thickening associated with perineural enhancement and intraconal fat involvement. Lumbar puncture revealed leukemic infiltration with blast cells after a week of eye symptoms, while bone marrow aspiration was negative for malignant cells. A diagnosis of left leukemic optic nerve infiltration with central retinal artery and vein occlusion was made. A high index of suspicion with repeat cerebrospinal fluid sampling is crucial to confirm the diagnosis as vitreous biopsy may fail to reveal infiltrative cells.