Recurrent Vasovagal Syncope in a Patient Receiving Pembrolizumab for Postoperative Pulmonary Metastases of Laryngeal Cancer: A Case Report

Immune checkpoint inhibitors (ICIs), such as pembrolizumab, are widely used for the treatment of various malignancies. Immune-related adverse events (irAEs), including neurological, endocrine, and cardiovascular complications, are known side effects of ICIs. Although syncope can occur as a manifestation of irAEs, vasovagal syncope (VVS), one of the most common causes of transient loss of consciousness, is not typically considered an irAE. Herein, we report a case of a 72-year-old man with postoperative pulmonary metastases from laryngeal cancer who underwent long-term pembrolizumab monotherapy. After completing 28 uneventful cycles, the patient experienced a transient episode of loss of consciousness immediately following the 29th infusion. The episode resolved spontaneously within a short period of time; however, the patient was admitted for evaluation. During this initial hospitalization, no further syncopal episodes occurred, and no remarkable abnormalities were found on cardiac, neurological, or endocrine assessments. The patient was discharged once his condition stabilized. However, shortly after discharge, he experienced a similar episode and was brought to our hospital. Upon arrival, his symptoms resolved, but he was readmitted for a second evaluation. During hospitalization, vasovagal syncope was diagnosed by the cardiology team based on head-up tilt testing and exclusion of other causes. The patient was managed using behavioral strategies and pharmacological therapy. Although pembrolizumab was temporarily suspended during the evaluation, it was resumed based on the confirmed diagnosis of VVS, absence of irAE-related findings, and a favorable oncologic response. This case emphasizes the importance of considering non-immune etiologies such as VVS in patients undergoing ICI therapy who present with transient loss of consciousness.