A Rare Case of Anti‐Yo Antibody Positive Paraneoplastic Neurologic Syndromes With EGFR Mutation Positive Non‐Small Cell Lung Cancer

Paraneoplastic neurologic syndromes (PNS) associated with anti-Yo antibody typically occur in females with ovarian or breast cancer, and their occurrence in lung cancer is rare. We report the first case of anti-Yo antibody positive PNS in a patient with EGFR mutation-positive non-small cell lung cancer (NSCLC). A 74-year-old male presented with acute vertigo and progressive cerebellar ataxia. Anti-Yo antibody was positive, and transbronchial biopsy confirmed papillary adenocarcinoma with EGFR exon 21 L858R mutation. Brain MRI also revealed multiple metastases, and cerebrospinal fluid cytology was positive for malignant cells. Despite the presence of brain metastases and leptomeningeal metastasis, neurological symptoms were attributed primarily to anti-Yo PNS based on clinical presentation. Chemotherapy was discontinued due to interstitial lung disease, but subsequent steroid therapy resulted in modest improvement of ataxic symptoms. This case suggests that NSCLC presenting with anti-Yo PNS may harbour EGFR mutations.