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

## TL;DR

A rare case of gluteal muscle metastasis from papillary thyroid cancer was detected using advanced imaging techniques after standard treatments failed.

## Contribution

Highlights the utility of 68 Ga-DOTATATE PET/MRI and 18 F-FDG PET/CT in detecting rare metastases unresponsive to iodine therapy.

## Key findings

- A painless gluteal mass was identified as metastatic PTC using combined imaging techniques.
- Muscle metastases are extremely rare in papillary thyroid cancer.
- Aggressive PTC variants show varied imaging affinities across modalities.

## Abstract

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.