Elevated thyroglobulin due to a back musculature schwannoma in differentiated thyroid cancer: a case report

Abstract

Case presentationOn 29 June 2021, a 36-year-old man with stage T4N1M0 differentiated thyroid cancer presented to the First Affiliated Hospital of Anhui Medical University for radioiodine therapy aimed at eliminating metastases.The patient had previously undergone bilateral radical thyroidectomy and remnant ablation with radioiodine therapy at another institution.The current treatment involved administration of 5.55 GBq (150 mCi) iodine-131 ( 131 I).Following 3 weeks of thyroid hormone withdrawal, laboratory results indicated a serum thyroglobulin (Tg) level of 44.99 ng/mL (reference range, 3.5-77), negative antithyroglobulin antibodies (A-Tg) [14.9 IU/mL; reference range, <115], and a markedly elevated thyroid-stimulating hormone (TSH) concentration exceeding 100 mIU/L (reference range, 0.27-4.20).Post-treatment 131 I whole-body scintigraphy ( 131 I-WBS) 3 days after radioiodine administration revealed no abnormal radioactive uptake lesions, except for physiological retention in the stomach and bladder (Fig a).During subsequent follow-up, the patient's serum Tg level decreased to 6.68 ng/mL with A-Tg of <10.0 IU/mL and remained stable for approximately 1 year.Nonetheless, repeat diagnostic 131 I-WBS on 7 July 2022 revealed that the stimulated Tg level had risen to 40.47 ng/mL with A-Tg level of 11.1 IU/mL.Imaging continued to show no evidence of abnormal radioactive uptake.Consequently, fluorine-18 fluorodeoxyglucose positron emission tomography/ computed tomography ( 18 F-FDG PET/CT) was performed to identify potential dormant lesions that did not exhibit iodine uptake.18 F-FDG PET/CT was performed on 8 July 2022.The maximum intensity projection showed a hypermetabolic lesion in the upper left chest (Fig b).Tomography fusion images showed a slightly hypodense soft tissue nodule measuring 2.5 × 2.1 cm 2 near the left erector spinae muscle at the fourth posterior rib level with an abnormal concentration