Immune checkpoint inhibitor-induced autoimmune limbic encephalitis with positivity for anti-Hu antibodies in a patient with small-cell lung cancer: A case report and literature review

In recent years, there has been an increasing number of studies on neurological symptoms induced as paraneoplastic neurological syndrome (PNS) or neurological immune-related adverse events (irAEs) in patients treated with immune checkpoint inhibitors (ICIs). Herein, we report a 68-year-old male patient with small-cell lung cancer who developed memory impairment and autonomic nervous system dysfunction after three courses of carboplatin, etoposide, and durvalumab therapy. Brain magnetic resonance imaging revealed hyperintense areas restricted to the bilateral temporal lobes. Moreover, based on the blood test results, the patient was strongly positive for anti-neuronal nuclear antibodies. Hence, he was diagnosed with autoimmune limbic encephalitis (ALE). Corticosteroid pulse therapy was administered. After treatment, the patient exhibited gradual improvement in memory impairment. However, while tapering the prednisolone dose, the patient exhibited relapse of memory disturbance owing to ALE. It is challenging to distinguish PNS from neurological irAEs. However, ICI-induced ALE with positivity for anti-Hu antibodies has an extremely poor prognosis.