Giant Cell Temporal Arteritis Followed by Severe Encephalopathy Induced by Immunotherapy in a Patient with Metastatic Renal Cell Carcinoma Achieving Durable Partial Response: A Case Report.

Introduction: Combined immuno-oncology (IO) regimens are the cornerstone of the current front-line systemic therapy for metastatic renal cell carcinoma (mRCC). Despite the fact that combined IO regimens show high efficacy, they are often accompanied by a wide spectrum of immune-related adverse effects (irAEs). Case Presentation: We describe a case of rare irAEs manifested as giant cell temporal arteritis (GCA) followed by severe encephalopathy occurring after continuing immunotherapy in a 66-year-old man with mRCC receiving a combination of ipilimumab and nivolumab in the first line of systemic therapy. GCA occurred 4 months after the initiation of IO and responded promptly to the low-dose prednisone therapy. Four months after the continuation of nivolumab maintenance, the patient was hospitalized due to severe irAE encephalopathy which presented as psycho-behavioral abnormalities and progressive cognitive decline. He was treated with high-dose methylprednisolone which led to complete resolution of the symptoms and IO was permanently discontinued. The patient achieved a durable partial response. Conclusion: Both GCA and the subsequent encephalopathy in our patient responded well to the corticosteroid therapy, leading to the complete resolution of the symptoms and the patient achieved a durable partial response. Although the risk of severe neurologic irAEs affecting the central nervous system induced by IO re-administration, following previous discontinuation due to irAE, is not well-defined because of their rarity, this case highlights the need for caution, particularly in cases with a history of previous irAE-associated GCA.