Anti-AMPAR limbic encephalitis as the initial presentation of metastatic small cell cancer.

A small proportion of small cell lung cancer (SCLC) presents as paraneoplastic limbic encephalitis (PLE). The most implicated antibody is anti-Hu, but others such as anti-ampiphysin, anti-CRMP5 and anti-SOX1 have been frequently detected. Autoimmune encephalitis mediated by antibodies against α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) is a rare but important neurological complication of SCLC. The incidence of SCLC presenting with anti-AMPAR antibody PLE is extremely low. Our case illustrates a rare presentation of SCLC with an intention to highlight the importance of evaluating for malignancy and associated paraneoplastic syndromes in patients with unexplained encephalopathy.