A Rare Presentation of Dizziness: Vestibular Testing in Paraneoplastic Cerebellar Degeneration.

Paraneoplastic cerebellar degeneration (PCD) is a rare neurological disorder caused by tumor-mediated antibodies targeting the cerebellum, often leading to irreversible cerebellar damage. The most common antibody implicated in PCD is anti-Purkinje cell cytoplasmic antibody type-1, associated with malignancies such as breast, gynecological, and lung cancers. Symptoms often include dizziness, imbalance, progressive ataxia, and other cerebellar signs/symptoms, but early presentations may mimic acute vestibular syndrome, thus complicating diagnosis. To present a case of PCD and demonstrate how objective vestibular test results facilitated the management of the patient’s medical care. Case report. A 67-year-old female with a history of left breast cancer presented with acute dizziness, imbalance, and left-sided lower-extremity weakness. The patient was referred for objective vestibular testing at the request of her internal medicine doctor. Vestibular testing revealed continuous down-beating nystagmus and abnormal video head impulse test (vHIT) findings of the posterior canals only. Findings and history raised concern for central vestibular origin. Subsequent neurological evaluations revealed progressive cerebellar dysfunction. After a long medical journey, anti-Yo antibodies were detected, confirming a diagnosis of PCD. PCD can present with early vestibular symptoms, such as vertigo and dizziness, and as a result of damage to Purkinje cells in the cerebellum. This damage extends to the central vestibular system structures, which can lead to down-beating nystagmus and impaired vestibular-ocular reflex function as evident by vHIT findings. Early vestibular testing can play a role in the diagnosis, particularly when accompanied by a detailed cancer history. Given the rapid disease progression of PCD, it is crucial for clinicians conducting vestibular testing to understand signs of central nervous system involvement and refer patients promptly for neurological evaluation.