Key Concepts
Introduction
Paraneoplastic neurological syndromes (PNS) are immune-mediated disorders in which a tumor expresses onconeural antigens (proteins normally restricted to the nervous system), triggering cross-reactive antibodies and T-cells that attack both tumor and normal neural tissue. Key antibody-syndrome associations include anti-Hu (ANNA-1) with small cell lung cancer causing sensory neuropathy and encephalomyelitis, anti-Yo (PCA-1) with ovarian/breast cancer causing subacute cerebellar degeneration, anti-NMDA receptor with ovarian teratoma causing limbic encephalitis with psychiatric symptoms, and anti-amphiphysin with breast cancer causing stiff person syndrome. PNS often precede cancer diagnosis by months to years, making neurological symptom recognition critical for early tumor detection. On the exam, writers often pair stable-sounding options with unstable data—notice the mismatch before you commit. If the stem names a license or role, reread that line; scope errors are classic trap answers even when the clinical topic is familiar. Run a 60-second scan: breathing work and oxygenation, perfusion and end organs, neuro baseline, likely infection sources, and devices that can fail quietly. When two answers feel partly right, pick the one that reduces imminent harm and matches orders for the role you...