Immune-related adverse events on 18F-FDG PET/CT in patients undergoing immune checkpoint inhibitor therapy

Introduction: Immune checkpoint inhibitors (ICI) act by inducing an anti-tumor immune response, which also leads to collateral immune targeting of the normal tissue, producing undesirable effects. These unique effects are termed as immune related adverse events (irAE) that can involve multiple tissues and organs and have a pooled incidence of ~50-70%. The detection of irAEs is important as it can prompt additional treatment or in severe cases, even cessation of ICI therapy.

¹⁸F-FDG PET/CT is frequently utilized for staging and assessing response in patients with various malignancies undergoing ICI therapy. Glucose metabolism targeting functional imaging with ¹⁸F-FDG helps in the early detection of several irAEs, even at sub-clinical stages. It is important for readers to be acquainted with the imaging features of irAEs, so that they may be promptly communicated to the referring clinician, and to avoid misdiagnosing them as disease involvement. Studies have also noted the association of appearance of irAEs with favourable treatment outcomes. In this context we present a review of the irAEs that are detected on ¹⁸F-FDG PET/CT, emphasizing on the imaging findings, their incidence and clinical relevance and a brief overview of their management.

Methods: We reviewed the medical and imaging records of patients who underwent ¹⁸F-FDG PET/CT after initiation of ICI therapy at our institution. Representative cases for irAEs were selected for inclusion in the exhibit, along with the supporting clinical information, treatment details and follow-up.

Results: This exhibit presents the ¹⁸F-FDG PET/CT findings in common and uncommon irAEs encountered during ICI therapy. These will be discussed tissue/ organ-system wise, emphasizing on the typical imaging features, clinical relevance, severity and management.

Conclusions: ¹⁸F-FDG PET/CT is superior to conventional imaging for detection of immune-related adverse events (irAE), especially those (e.g. pneumonitis, colitis, hypophysitis, adrenal insufficiency) that may require cessation of therapy. Recognition of irAE associated imaging patterns on ¹⁸F-FDG PET/CT is important for the interpreting nuclear medicine physicians to avoid mis-diagnosis and facilitate institution of appropriate medical care.

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