Endocrine Abstracts

Introduction: Differentiated thyroid cancer (DTC) accounts for 90% of all thyroid cancers. The majority of DTC have a favourable outcome, but 5–10% of the patients will develop metastatic disease. Functioning metastases of differentiated thyroid cancer are very rare and their pathogenesis is still not fully understood.

Case report: We present the clinical course and management of a 71-year-old woman diagnosed with subclinical non-autoimmune hyperthyroidism. A nodule in the left thyroid lobe with high risk ultrasound features was found and fine needle biopsy (FNB) was performed with a cytological result of Bethesda category 3. Considering the ultrasound characteristics of the nodule the patient was referred for a lobectomy. The surgical treatment was postponed by the patient for personal reasons. Three months later, a MRI study was done for back pain and disseminated bone metastases were found, initially interpreted as being with pulmonary origin because of a coexisting pulmonary mass. Subsequently, a PET/CT and a bone biopsy with immunohistochemical staining suggested thyroid origin. The repeated FNB and cytology of the same nodule yielded a follicular lesion – Bethesda category 4. The bone findings were interpreted as metastatic thyroid cancer and a total thyroidectomy was done. The pathology report described invasive follicular thyroid cancer. The patient was referred for radioiodine ablation. Suppressed TSH and high FT4 were found just before the intake of radioiodine despite the discontinuation of oral levothyroxine for one month. The post-therapeutic whole body scan (WBS) showed multiple foci of increased uptake in the bones. The hyperthyroidism persisted after the radioiodine ablation. The patient underwent a second radioiodine therapy after rhTSH stimulation. The post-therapeutic WBS revealed persistence of the foci with increased uptake in the skeleton. A reduction of T3 and T4 was observer three months later. A third radioiodine therapy is scheduled.

Conclusion: Functional metastatic thyroid cancer is a rare phenomenon and must be considered when evaluating thyroid cancer with concurrent hyperthyroidism. The presented case illustrates the diagnostic and therapeutic challenge posed by autonomous hormone production from metastatic FTC.