False-positive Findings of Large Vessel Vasculitis on FDG-PET in Patients Treated With Immune Checkpoint Inhibitors

Fluorine-18 fluorodeoxygluocose positron emission tomography (FDG-PET) is increasingly used in the evaluation of response to immune checkpoint inhibitor (ICI) therapy. Incidental findings of increased vessel wall uptake may prompt the concern for ICI-induced large vessel vasculitis (LVV). Precise radiographic and clinical evaluation is required to determine if this represents true vasculitis, as use of immune suppression and ICI discontinuation can have significant impacts on patient outcomes. We performed a retrospective case analysis of 4 consecutive patients referred to 2 rheumatology clinics treated with ICI with incidental findings of LVV on FDG-PET, reviewing their clinical course and radiographic findings. All 4 cases had FDG-PET scans for routine oncology indications and had no associated clinical features of LVV. One patient was treated with corticosteroids and no patients developed any clinical evidence of vasculitis during a mean follow-up period of 17 months (range: 7-33 mo). All FDG-PET images reporting LVV underwent a standardized analysis to identify any technical issues or concerns with interpretation. In review of imaging, 3 of the cases may have been due to delayed tracer to scan interval leading to misinterpretation of vascular uptake as suspected LVV. Recognition of technical pitfalls in FDG-PET interpretation is crucial to inform the need for immunosuppression and the safety of continued ICI therapy.