Isolated Pericardial Effusion Without Associated Myocarditis in a Small-Cell Lung Cancer Patient Undergoing Atezolizumab Therapy.

Immune checkpoint inhibitors (ICIs) are a form of immunotherapy increasingly utilized in cancer therapies. While offering promise in malignancy treatment, ICIs, including atezolizumab, can elicit immune-related adverse events (irAEs) such as cardiotoxicity. We present the case of a 67-year-old male with stage IV metastatic small-cell lung cancer undergoing carboplatin, etoposide, and atezolizumab therapy, who developed pericardial tamponade two months into treatment. Initially presenting with hypoxia on day three of his third treatment cycle, he was admitted due to multifocal pneumonia and subsequently diagnosed with pericardial tamponade stemming from a sizable pericardial effusion. Pericardiocentesis was performed, effectively resolving the tamponade. Infectious etiology was ruled out. Notably, there was no associated myocarditis, as evidenced by negative cardiac markers and magnetic resonance imaging (MRI) findings, and cytologic analysis of the pericardial fluid did not reveal malignant cells, indicating an isolated immunologic etiology for the pericardial effusion. Following successful management, including oxygen support and a prednisone taper, chemotherapy without immunotherapy was resumed after a one-week delay. This rare case underscores the significance of promptly utilizing multimodality imaging with timely cardiology intervention, a prompt pericardial fluid analysis in diagnosing cardiac irAEs, and management leading to improved patient outcomes.