Pembrolizumab Induced-Encephalitis in An Elderly Patient with Nasal Angiosarcoma: A Case Report

Introduction New immunotherapies are increasingly being used as treatment for different types of malignancies. Immunotherapeutic agents such as immune checkpoint inhibitors (ex. pembrolizumab) have been associated with various side effects, including encephalitis. Pembrolizumab, a monoclonal antibody which mechanism of action consists of activity against programmed cell death antigen (PD-1) has been associated with encephalitis. Methods We present the case of a 76-year-old man with past medical history of angiosarcoma of the nose that was treated with radiation, chemotherapy with Taxol. Due to the patient\u0027s high tumor mutation burden, he began treatment with pembrolizumab. After six months of treatment with pembrolizumab, he presented to the emergency department with acute changes in mentation. The patient was confused and wanted to go to vote in the middle of the night. He was waking up every 30 minutes and exhibited disorganized thought process and visual hallucinations. Full delirium work-up was done without any major findings. The following tests were in the normal range or negative: thyroid function tests, prolactin, LH, cosytropin stimulation test, ACTH, UA, CBC and CMP. Brain MRI excluded evidence of acute intracranial findings, acute ischemia or brain metastases. Psychiatry was consulted. Pembrolizumab was stopped. Recommendation was made to start aripiprazole 5mg daily. Patient improved after implementing these measures. Results We postulate that the patient developed encephalitis triggered by pembrolizumab in the context of angiosarcoma of the nose. Autoimmune encephalitis is a rare adverse effect of immune checkpoint inhibitors but it may be severe and potentially lethal. The etiology is not known and diagnosis can be challenging. We postulate that the patient developed encephalitis triggered by pembrolizumab in the context of angiosarcoma of the nose. Conclusions This case highlights the need of psychiatrists to understand the behavioral symptoms that could be attributed to immunotherapy agents in patient undergoing cancer treatment. Early identification and treatment of the behavioral symptoms are important in order to evaluate and manage appropriately, especially in the elderly population. It is important to consider autoimmune encephalitis secondary to immunotherapy as a differential for psychiatric disorders. Funding No funding