Localization of F-18 fluorodeoxyglucose (FDG) has been described before in inflammatory conditions of the thyroid, particularly chronic thyroiditis. The differential diagnosis would include adenomatous goiter, acute or subacute thyroiditis, anaplastic carcinoma, malignant diffuse lymphoma, and Graves' disease. The increased uptake in Graves' disease may follow a mechanism similar to that of uptake in chronic thyroiditis, as both are autoimmune diseases, but the exact mechanism is still unknown. Graves' disease is characterized by cell hyperplasia, usually is accompanied by lymphocytic infiltration, and correlates with levels of antithyroid antibodies in the blood. This case involves an untreated patient with documented Graves' disease, which was first discovered in an F-18 FDG study that was requested to evaluate the extent of recently diagnosed head and neck cancer. The imaging study revealed intense uptake of F-18 FDG in both thyroid lobes.
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