Fatal limbic encephalitis as paraneoplastic neurological syndrome in a patient with lung adenocarcinoma positive for antiamphiphysin antibody after durvalumab treatment

A 69‐year‐old Japanese male with advanced lung adenocarcinoma developed neurological symptoms after chemoradiotherapy and durvalumab maintenance therapy. He was positive for serum antiamphiphysin antibody, which is rarely seen in patients with lung adenocarcinoma. Additionally, his brain magnetic resonance images showed limbic encephalitis which led to the diagnosis of classic paraneoplastic neurological syndrome (PNS). Immune checkpoint inhibitors (ICIs) activate T cells and may also activate antineuronal antibodies that cause PNS. Durvalumab, which is an ICI, may have led to antiamphiphysin antibody‐positive PNS in our patient. Treatment with systemic high‐dose methylprednisolone was unsuccessful and he died 2 months later. PNS should be considered as one of the differential diagnoses in patients with lung cancer and neurological symptoms during, or after, ICI treatment.