Paraneoplastic cerebellar degeneration diagnosed by anti-Yo determination in a young woman with early breast cancer.

A 44-year-old woman diagnosed with a HER2 positive early breast cancer, receiving neoadjuvant treatment with paclitaxel and targeted agents, trastuzumab together with pertuzumab, presented to the emergency room with gait instability and upper right limb weakness. The neurological examination was compatible with cerebellar alteration showing right dissymmetry of the finger-nose and heel-knee manoeuvre. A head CT and a brain MRI were performed and negative. The electromyography showed alterations of the pyramidal pathway and somatosensory pathway. In order to determine the cause of the cerebellar affection, a lumbar puncture was performed. The cerebrospinal fluid analysis was non-specific, but the antineuronal anti-Yo antibody was positive, being diagnosed of a paraneoplastic cerebellar degeneration (PCD). A positron emission tomography CT ruled out metastatic disease. The patient completed four cycles of antiHER2 blockade and weekly paclitaxel, achieving a complete pathological response. One year later, she maintains a complete remission but the PCD still prevails.