Role of [18F] FDG PET-CT in detection of COVID-19 vaccine-associated hypermetabolic lymphadenopathy (VAHL) in lymphoma patients: with serologic testing correlation

BACKGROUND: COVID-19 vaccination of the population has a great importance, especially in oncological patients. The high incidence of vaccine-associated hypermetabolic lymphadenopathy (VAHL) makes a difficulty in the diagnosis of PET-CT of oncological patients. They should be vaccinated in the side opposite to the expected malignant LNs to avoid unnecessary biopsy and change in therapy. The aim of this study was to assess the role of PET-CT in detection of VAHL after the 2nd dose of Pfizer-BioNTech vaccine in lymphoma patients and compare the incidence of VAHL among lymphoma patients treated with B cell depletion therapy during the 6 months prior to vaccination and those treated > 6 months before vaccination. RESULTS: This study comprised 120 lymphoma patients, referred for FDG PET/CT 1–3 weeks after the 2nd dose of Pfizer-BioNTech COVID-19 vaccine. Hypermetabolic LNs were identified in 55%. The incidence of VAHL in lymphoma patients treated with anti-CD20 antibody rituximab during the 6 months prior to vaccination (9%) was significantly lower compared with other lymphoma patients treated with anti-CD20 antibody rituximab > 6 months before vaccination (91%). The incidence and grades of VAHL are significantly high within the 1st week after the 2nd dose of Pfizer-BioNTech vaccine in patients younger than 60 years of age. Only 7 of 37 patients with negative serology had VAHL on PET-CT, whereas 10 of 26 patients with decreased anti-spike titers and 49 of 57 patients with increased anti-spike titers had VAHL on PET-CT. CONCLUSIONS: VAHL makes challenges in the interpretation of FDG PET/CT in oncology patients. Accurate data collection, regarding the time and site of COVID vaccination, is important to help radiologists in identifying the cause of abnormal nodal FDG uptake. We suggest to schedule FDG PET-CT for lymphoma patients at least 3 weeks after the 2nd dose of Pfizer-BioNTech vaccine.