Optic neuropathy in cancer patients. Report of a case possibly related to 5 fluorouracil toxicity and review of the literature.

We report the case of a 72-year-old woman suffering from bone metastatic breast cancer and treated with continuous intravenous 5 fluorouracil (5FU) chemotherapy, who presented with a bilateral asymmetric anterior optic neuropathy (ON). A deficiency of dihydropyrimidine dehydrogenase (DPD) was documented. Patients with DPD deficiency are at increased risk for developing unusual and/or severe toxicity to 5FU. We discuss the differential diagnosis of anterior ON and we suggest that 5FU can be responsible for optic nerve toxicity in patients with DPD deficiency.