COVID-19 vaccination induced axillary nodal uptake on [18F]FDG PET/CT.

Worldwide mass COVID-19 vaccination is being deployed. A 76-year-old female with oligosecretory myeloma disease underwent follow-up [18F]FDG PET/CT, which demonstrated no definite [18F]FDG avid disease; however, an avid left axillary node and superficial uptake in the left upper arm were noted.

[18F]FDG PET/CT maximal intensity projection (MIP) (a) demonstrate focal uptake in the left axilla (arrow) and ill-defined subcutaneous uptake in the left arm (arrowhead). Tracer injection was via the right antecubital fossa. Coronal and axial CT, [18F]FDG PET, and fused [18F]FDG PET/CT of the chest (b–g) demonstrate low-grade uptake within the subcutaneous soft tissues superficial to the left deltoid (arrowheads) and within a level I left axillary node (arrows).

The patient had been administered the Oxford-AstraZeneca COVID-19 vaccination in the left upper arm 2 weeks earlier. Subcutaneous uptake adjacent to the deltoid is in keeping with the recent injection. On reviewing the CT component and correlating with the clinical history, the nodal uptake was concluded to be reactive, related to the recent vaccination. A similar case was described with Pfizer-BioNTech COVID-19 vaccination in January 2021 [1].

This case highlights a new [18F]FDG PET/CT pitfall associated with the current COVID-19 pandemic that reporters should be made aware of, to avoid potential disease upstaging and overtreatment.