Endocrinology Fellow Henry Ford Health System Royal Oak, Michigan, United States
Introduction : Metastases to the thyroid have a low reported incidence, with a frequency of 2-4% among all thyroid malignancies. In autopsy series, lung cancer is reported to be the most common primary tumor, while clinically, renal cell cancer is the most common. Most thyroid metastases presentas unifocal nodules; however, diffuse metastases are less often seen. Patients are euthyroid at presentation, and hyperthyroidism is very rarely reported.
Case(s) Description : A 74-year-old man was referred for evaluation of hyperthyroidism. Initial symptoms included palpitations and weight loss. TSH was < 0.01 uIU/mL (0.40 - 7.50), free T4 3.08 ng/dL (0.61 - 1.44), total T3 125 ng/dL (87 - 178). TSI was negative. Evaluation of weight loss prompted a CT chest which revealed several lung nodules and enlarged mediastinal and hilar lymph nodes. Incidental finding of punctate calcification was reported in the left thyroid lobe with no distinct thyroid nodules. Staging 18F-FDG-PET CT revealed intense uptake in bilateral thyroid lobes, initially thought to be related to active hyperthyroidism. Biopsy of a right supraclavicular lymph node was performed, and pathological evaluation revealed metastatic lung cancer. Given intense uptake in the thyroid on PET, neck ultrasound was performed and revealed bilateral heterogeneous appearing thyroid gland with numerous diffuse punctate echogenic foci with no discrete nodules and several morphologically abnormal lymph nodes. Random fine needle aspiration of bilateral thyroid lobes and left cervical lymph node was performed and was positive for lung adenocarcinoma. Core needle biopsy of right lung mass revealed adenocarcinoma. On follow up, thyroid labs spontaneously normalized, consistent with thyroiditis. Molecular testing guided treatment with Capmatinib.
Discussion : Hyperthyroidism as an initial presentation of thyroid malignancy is rare as most patients are euthyroid.In this case, we speculate that aggressive invasion of tumor cells into the thyroid resulted in thyroiditis.Additionally, diffuse echogenic foci in the thyroid are uncommonly seen in metastatic thyroid disease, which usually presents as single or multiple nodules.Diffuse uptake on PET CT has been shown to be associated with benign autoimmune thyroid disease while malignant lesions usually have focal uptake. However, in the setting of an underlying malignancy, this case highlights that a diffuse uptake should not be regardedas abenign finding. Random bilateral thyroid biopsies should be performed in patients who have positive diffuse FDG-PET uptake, without a discrete nodule, in patients known to have an underlying non-thyroidal malignancy.
