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Fluorine-18 Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in Hodgkin's Lymphoma: Diagnostic Challenge during COVID Vaccination
Address for correspondence: Dr. Sharjeel Usmani, Department of Nuclear Medicine, Kuwait Cancer Control Center (KCCC), PO Box 1488, 83001 Khaitan, Kuwait. E-mail: dr_shajji@yahoo.com
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Abstract
Benign metabolic uptake on fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG PET) is not uncommonly seen after immunization. We report a case of 30-year-old man with Hodgkin's lymphoma who underwent two cycles of chemotherapy. Interim 18F-FDG PET/computed tomography demonstrated complete metabolic response of prior hypermetabolic bilateral supraclavicular and mediastinal lymph nodes. Although multiple new normal-sized hypermetabolic left axillary and subpectoral lymph nodes are noted, relevant history revealed COVID vaccine 7 days prior scan with mild FDG uptake at the left deltoid muscle. These new findings at the left axilla are likely related to recent vaccination. 18F-FDG PET uptake in the lymph nodes is not so uncommon after immunization; relevant history is very important especially in the phase of massive immunization to avoid false interpretation.
Keywords
Fluorine-18 fluorodeoxyglucose positron emission tomography
COVID-19
vaccination
A 30-year-old male who has Hodgkin's lymphoma underwent two cycles of chemotherapy. Interim fluorine-18 fluorodeoxyglucose positron emission tomography (18F-FDG PET) post 7 days of first dose of Oxford COVID vaccine at the left deltoid muscle. Baseline 18F-FDG PET/computed tomography (18F-FDG PET/CT) shows hypermetabolic bilateral supraclavicular and mediastinal lymph nodes [Figure 1]. Interim 18F FDG PET images demonstrate complete metabolic resolution of prior supraclavicular and mediastinal lymph nodes [Figure 2]. There are multiple new normal-sized hypermetabolic left axillary and subpectoral lymph nodes that are noted along with mild increase tracer uptake in the left deltoid muscle. Subsequent ultrasonography of the axilla also revealed normal-looking lymph nodes. Keeping in view of history, these new findings at the left axilla are likely related to recent vaccination, a diagnosis of benign 18F-FDG uptake in the normal-sized axillary lymph nodes is made, and the follow-up is advised.
18F-FDG PET is enormously used in diagnostic staging, restaging, and response evaluation in cancer patients; however, these findings are nonspecific for cancers and can also found in inflammatory and infectious conditions.[12] 18F-FDG PET has shown a high overall accuracy in predicting treatment outcome in lymphoma, both during and after completion of treatment; despite that, a study carried out at an interim time point of therapy may not be able to discriminate between the presence of residual viable neoplastic tissue and a nonspecific inflammatory host response.[3] In literature, false-positive 18F-FDG uptake within the lymph nodes is reported after vaccination and has the highest probability if vaccination was administered <8 days before the scan.[4] Increased FDG activity in the ipsilateral deltoid muscle is a key finding for accurate interpretation of increased FDG activity in the axillary lymph nodes.[56] However, Ayati et al.[7] also reported a case of generalized lymph node activation postinfluenza vaccination.
18F-FDG PET uptake in the lymph nodes by metabolically active tissue due to vaccine-related immune response has been encountered beforehand, and it is considered as a potential pitfall in images interpretation.[89] Evidence in the literature has documented that the availability of clinical history increases the accuracy of radiologic image interpretation.[10] The role of clinical history is well established in 18F-FDG PET/CT study reporting more significantly in initial interim scans of lymphoma patients as results may alter the management plan considerably that the role was greatly emphasized by the presented case.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
Acknowledgment
We would like to acknowledge Dr. Rashid Rasheed and Dr. Muneera Al Maraghy.
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