Brown Adipose Tissue Mimicking Head and Neck Cancer on PET Scan in a Patient on GLP-1 Drug.

To report a case of a patient undergoing GLP-1 receptor agonist therapy in which increased FDG uptake in brown adipose tissue (BAT) mimicked metastatic head and neck cancer on PET/CT imaging. A 61-year-old female with Class III obesity presented with a right-sided neck mass after significant weight loss following the use of the GLP-1 receptor agonist, Semaglutide. PET/CT revealed FDG uptake in the right level II lymph node and extensive BAT uptake throughout the neck and mediastinum, complicating the diagnosis.