Work

SAT-584 Skeletal Muscle and Bone Metastases in Papillary Thyroid Microcarcinoma

Year: 2024

Type: article

Abstract: T. Tselovalnikova: None. S. Tadisina: None. Y. Almontasib: None. S. Dukkipati: None. E.T. Ngo: None. R. Asad: None. L.G. Weide: None. Introduction: Thyroid cancer is usually localized but 30% of them can metastasize to other organs. While lymph nodes and lungs are considered common sites for metastasis, skeletal muscle metastasis is very rare. Case presentation: A 47-year-old male initially underwent left hemithyroidectomy for a thyroid nodule reported as benign per patient without available pathology. Over a decade later, he noticed a lump on his neck while shaving. Thyroid ultrasound (US) showed a left 1.9 cm nodule with calcifications. Fine needle aspiration (FNA) biopsy revealed atypical cells of undetermined significance (AUS). The remaining left thyroid tissue was resected, and surgical pathology confirmed benign hyperplastic nodule. Follow up US at six months showed a new nodule of 0.9 cm in the right lobe. Follow up US one year from the surgery revealed increase in size of the right nodule to 1.1 cm with new microcalcifications and a new nodule of 1.6 cm in posterior right middle lobe was also noted. FNA biopsy of both these nodules was negative for malignancy. Three years later, further growth from 1.1 to 2.8 cm was noted in one of the nodules but the repeat FNA biopsy was benign. During this time, the patient reported a lump on left deltoid muscle, which was excised, and pathology revealed nodular thyroid tissue with mild atypia. Thyrogen I-131 Whole Body Scan showed increased uptake in the thyroid bed and in the left iliac crest and sacrum. A completion thyroidectomy was done and the surgical pathology showed a 0.17 cm papillary thyroid microcarcinoma with follicular variant. Levothyroxine was started and the patient is currently awaiting radioiodine (RAI) ablation. Discussion: Thyroid carcinoma most commonly metastasize to locoregional lymph nodes and lungs. Our patient was diagnosed as papillary thyroid microcarcinoma with a follicular variant, which is considered low risk and usually cured by surgical resection. However, he was found to have metastases to the deltoid muscle and sacroiliac region. Thyroid cancer does not usually bypass the common sites and spread directly to the muscle and bone. Skeletal muscle metastasis is extremely rare for both papillary (PTC) and follicular thyroid cancer (FTC). As reported in 2018, only 45 cases of skeletal muscle metastasis were observed in both PTC and FTC over 110 years. Among them, the most frequent site was the gluteus muscle. While deltoid muscle metastasis was reported in only two cases as these cases are uncommon, treatment strategies are based on an expert opinion rather than well-established guidelines. The main approach is surgical resection followed by systemic therapy, either RAI or tyrosine kinase inhibitors (sorafenib or sunitinib) in non-iodine avid metastasis. Despite the suggested treatment, the median prognosis is variable in these metastatic diseases, ranging from 12-24 months. Saturday, June 1, 2024

Source: Journal of the Endocrine Society

DOI: 10.1210/jendso/bvae163.2447