Upbeat Nystagmus & Ocular Flutter Due to Cerebellar Pilocytic Astrocytoma

This is a 20-year-old woman who was diagnosed with a cerebellar pilocytic astrocytoma at age 10 after presenting with severe headaches and hydrocephalus. She underwent incomplete resection and radiation therapy at that time. She experienced mild vertical oscillopsia in upgaze at baseline, and increased vertical oscillopsia in primary gaze several times over the years due to shunt failure. Two years prior to this video recording, she first experienced intermittent horizontal oscillopsia. MRI did not demonstrate tumor progression, and she was otherwise clinically stable. The following ocular motor exam findings were seen at the time of this video: 1) spontaneous upbeat nystagmus (UBN) increasing in right and up gaze (explaining her vertical oscillopsia) along with gaze-evoked nystagmus (mainly in right, up, down gaze), also with UBN increasing during convergence, and 2) intermittent horizontal oscillations without an intersaccadic interval (on eye movement recordings) consistent with ocular flutter. As expected, ocular flutter increased with convergence and following saccades, both of which have been described. Given the relatively more recent onset of ocular flutter (per the history of new horizontal oscillopsia), she underwent a work-up for inflammatory, infectious, autoimmune, neoplastic/paraneoplastic etiologies, which was unrevealing. In the end, it was thought that the ocular flutter (which was present for well over 1 year) was a late consequence of her previous radiation therapy and surgery for cerebellar pilocytic astrocytoma. Seen on her MRI was a stable small enhancing lesion posterior to the fourth ventricle with adjacent gliosis compatible with residual pilocytic astrocytoma. There was also signal abnormality within the right superior cerebellar peduncle as well as the left medullary olive with volume loss of the right inferior cerebellar peduncle, consistent with hypertrophic olivary degeneration.