Iodine-Negative Rare Gluteal Muscle Metastasis of Papillary Thyroid Cancer: Detected by 68Ga-DOTATATE PET/MRI and 18F-FDG PET/CT

The case presents a 57-year-old male with metastatic papillary thyroid carcinoma (PTC) to the lymph nodes, lung, and mediastinum. Despite receiving multiple high-dose radioactive iodine (RAI) therapies, the patient's serum thyroglobulin levels continued to rise. The patient, who was unresponsive to RAI therapy, was being evaluated for suitability for ¹⁷⁷ Lu-DOTATATE therapy. Therefore, after the third high-dose treatment, simultaneous ⁶⁸ Ga-DOTATATE PET/MRI and ¹⁸ F FDG PET/CT imaging were performed, revealing a painless mass in the left gluteal region. The gluteal mass was excised, and histopathology confirmed it as metastatic PTC. Muscle metastases are extremely rare for PTC. This case exemplifies the different levels of tumoral affinity shown by aggressive variants of PTC across three distinct imaging modalities: ⁶⁸ Ga-DOTATATE PET/MRI, ¹⁸ F FDG PET/CT, and whole-body iodine scintigraphy.