Optic neuropathy: a rare paraneoplastic syndrome.

A 63-year-old man developed gradually progressive bilateral loss of vision, cerebellar ataxia, and downbeat nystagmus. Visual acuity was 20/400 OD and 20/200 OS, with cecocentral scotomas OU. Fundus examination showed bilateral optic atrophy and a vitreous cellular reaction. MRI of the brain was normal. CSF protein was elevated, with increased IgG levels but no malignant cells. Biopsy of a pulmonary lymph node showed undifferentiated small cell carcinoma. Neoplastic cells were positive for neuron-specific enolase. Serum contained IgG, which reacted with neuronal and glial cytoplasm and processes. IgG reactivity with systemic tissues and the patient's tumor was not different from that observed with control sera. Paraneoplastic optic neuropathy should be considered in patients with unexplained visual loss and malignancy, and our observations suggest a possible immunologic basis for this condition.