Following a nonspecific prodrome of dizziness lasting one month, a 57-year-old female presented with three months of gait instability, dysarthria, and memory difficulties. Neurological examination revealed memory and attention deficits, difficulty naming objects, tangential speech, wide-based gait, reduced saccadic velocities, and appendicular dysmetria. Brain MRI was normal. Seven nucleated cells were found on CSF analysis with 92% lymphocytes, elevated protein (48 mg/dL), normal glucose (64 mg/dL), and negative cytology. An elevated IgG index (1.45) and oligoclonal bands were present. CT chest/abdomen/pelvis identified a suspicious 1.1 cm right axillary lymph node, while breast examination, mammogram, ultrasound, and breast MRI revealed no disease. Whole-body PET showed the axillary node was FDG-avid. Biopsy demonstrated HER-2 positive adenocarcinoma suspicious for breast origin. Serum and CSF contained anti-Yo antibodies.
Following five days of intravenous methylprednisolone and immunoglobulin, gross total resection of the right axillary lymph node, and chemotherapy with carboplatin, trastuzumab, and pertuzumab, her cognitive symptoms nearly resolved, and coordination improved four months later.