[18F]FDG PET/CT imaging in hyperthyroid myopathy presenting initially as myasthenia: a case report

Background Muscle weakness can be a clinical manifestation of a wide range of diseases, often with an obscure etiology and a high risk of misdiagnosis. [ 18 F]FDG PET/CT has been widely studied in tumors and inflammatory myopathies; however, reports on [ 18 F]FDG PET/CT imaging of hyperthyroid myopathy are exceedingly rare, particularly in patients with a history of malignancy, in whom the diagnostic process is especially challenging. Case A 51-year-old woman presented with bilateral lower-limb weakness of more than 1 year’s duration without an obvious precipitating factor. She had undergone surgery and chemotherapy for endometrial carcinoma 2 years earlier. Whole-body [ 18 F]FDG PET/CT demonstrated diffusely increased [ 18 F]FDG uptake in skeletal muscles throughout the body, with a maximum standardized uptake value (SUVmax) of 5.7. Both thyroid lobes were enlarged, with decreased density and diffusely increased [ 18 F]FDG uptake (SUVmax 3.1). Post-treatment changes of endometrial carcinoma were noted, with no evidence of metabolically active tumor recurrence or metastasis. Laboratory tests revealed elevated thyroid hormone levels and a thyroid-stimulating hormone level