Severe edema as an immune-related adverse event following nivolumab therapy: a case report.

Background: Immune checkpoint inhibitors (ICIs) are widely used to treat various cancers and can cause immune-related adverse events (irAEs). These adverse events may affect multiple organs and occasionally become life-threatening. Fluid retention, including pleural or pericardial effusion, has been reported as a manifestation of irAEs; however, generalized edema is rare and its clinical characteristics remain poorly described. We present a case of a patient who developed generalized edema and weight gain as irAEs, posing diagnostic and therapeutic challenges. Case Description: A 78-year-old man developed severe generalized edema and significant weight gain following nivolumab therapy for recurrent lung cancer. Extensive evaluations were performed to determine the cause of the edema. Laboratory findings and imaging studies did not reveal cardiac failure, renal dysfunction, or hepatic disease that could explain the symptoms. The edema was refractory to diuretic therapy. Based on these findings, the condition was diagnosed as ICI-induced edema. Edema and weight gain improved rapidly after corticosteroid administration, suggesting an immune-mediated mechanism related to immune checkpoint inhibition. The corticosteroid was gradually tapered in the outpatient setting, and no recurrence of edema or weight gain occurred during follow-up. Conclusions: ICI-induced edema is a rare irAE that may result from increased capillary permeability secondary to immune-mediated vascular inflammation. Because edema can mimic cardiac, renal, or hepatic disorders, comprehensive evaluation is essential to exclude common causes. ICI-induced edema may progress to more severe irAEs, such as pleural or pericardial effusion. Clinicians should consider immune-related edema in the differential diagnosis when unexplained fluid retention occurs during ICI therapy. Early recognition and prompt initiation of corticosteroid therapy are crucial to prevent life-threatening complications.