Cerebellar Degeneration Causing Saccadic Dysmetria and Ocular Flutter: A Seronegative Paraneoplastic Syndrome

We describe a 68-year-old woman with metastatic small cell lung cancer, in remission, who presented with several months of moderately progressive truncal, gait ataxia, followed by development of saccadic dysmetria and ocular flutter. CSF analysis revealed lymphocytic pleocytosis, normal protein and glucose, with four oligoclonal bands. She was diagnosed with a probable paraneoplastic syndrome and successfully treated with high dose intravenous methylprednisolone and plasmapheresis, with resolution of eye movement abnormalities, and improvement of ataxia. In this case, ocular flutter might have been caused by indirect instability of the brainstem network due to impairment of the FOR projections to the omnipause neurons (OPN) in the pontine saccadic burst generator area. Identifying which patients with cancer may benefit from immunotherapy remains a challenge. Our case suggests that seronegative cerebellar paraneoplastic syndromes may at least partially respond to immunotherapy with methylprednisolone and plasmapheresis, which should be considered early on in the treatment plan.