PD-1-induced encephalopathy: a report of 2 cases on neurological toxicities with immune checkpoint inhibitors.

Background: Immune-related adverse effects (irAEs) often occur during immune checkpoint inhibitor (ICI) therapy. In the nervous system, the incidence of irAEs ranges from 0.1-12%, with 80% occurring within the first 4 months of ICI application. For complications of the nervous system, adequate diagnosis is made by signs, symptoms, imaging and cerebrospinal fluid. If severe irAEs occur, ICIs should be discontinued and patients should be treated with high-dose glucocorticoids, immunoglobulins, or immunosorbent therapy with systemic support. Patients who develop severe neurologic irAEs have a poorer prognosis. Case Description: In this article, we report 2 cases of encephalopathy induced by anti-programmed cell death protein 1 (PD-1) monoclonal antibodies at the initial diagnoses. Our findings may help clinicians to differentiate between encephalopathy caused by immunotherapy and other neurological disorders. Case 1 was a 24-year-old male patient who had undergone PD-1 immunotherapy to treat olfactory neuroblastoma. After the 6th course of therapy, he began to develop persistent epilepsy, which decreased significantly after high doses of glucocorticoid and immunosorbent therapy were administered. Based on his medical history and laboratory examination results, PD-1-induced encephalopathy was the most likely diagnosis. Case 2 was a 67-year-old female patient who had been treated with PD-1/programmed death ligand-1 therapy for lung adenocarcinoma. She began to have headaches after 1 cycle of treatment, and her cognitive function gradually decreased with the continuation of immunotherapy. Conclusions: These case reports show the difficulty in distinguishing PD-1-induced encephalopathy from other neurological disorders, especially paraneoplastic neurological syndromes. If not treated properly, patients' lives may be endangered. Thus, early identification and early treatment are very important.