Delayed-onset seesaw nystagmus following brain irradiation.

Seesaw nystagmus (SSN) is a rare, debilitating neurologic syndrome with few known etiologies. Typically, patients present with oscillopsia subsequent to a recent neurologic insult, with only a handful of patients showing delayed onset after trauma. We report a case of seesaw nystagmus in a patient with a large meso-diencephalic mass treated with external beam radiation therapy (XRT), who developed asymptomatic SSN nearly 8 years after treatment.