(18)F-FDG PET/CT imaging of atypical subacute thyroiditis in thyrotoxicosis: A case report

BACKGROUND: In addition to its established role in oncologic imaging, (18)F-fluorodeoxyglucose positron emission tomography/computed tomography ((18)F-FDG PET/CT) is useful for the assessment of inflammatory activity. However, subacute thyroiditis (SAT) in thyrotoxicosis is rarely detected during these scans. CASE: A 66-year-old man with SAT in thyrotoxicosis demonstrated symptoms of transient fatigue, headache, and fever, without typical neck pain. Using (18)F-FDG PET/CT, we found increased (18)F-FDG uptake in the thyroid gland, predominantly in the right side due to SAT. We also observed a coexisting decrease in (18)F-FDG uptake in the liver and increased (18)F-FDG uptake in skeletal muscle due to thyrotoxicosis. CONCLUSION: Using (18)F-FDG PET/CT, the combined observations of increased (18)F-FDG uptake in the thyroid and skeletal muscle, and decreased (18)F-FDG uptake in the liver, even when the typical symptom of neck pain is subtle or absent, may be helpful for the differential diagnosis of SAT in thyrotoxicosis.