Metastatic Follicular Thyroid Carcinoma of the Proximal Humerus 20 Years after Subtotal Thyroidectomy: A Case Report and Literature Review

Though rare, metastatic thyroid carcinoma may present as thyrotoxicosis. We present a case of thyrotoxicosis caused by metastatic follicular thyroid carcinoma in the right proximal humerus. A 75-year-old female presented with pain and movement restriction of her right proximal upper arm for 1 month. She received a bilateral subtotal thyroidectomy 20 years ago for thyroid cancer. Images from roentgenogram and magnetic resonance (MR) studies revealed a lobulated mass arising from the proximal humerus. Her thyroid stimulating hormone (TSH) level was non-detectable, and free T4 was 0.8 ng/dl. A bilateral radical thyroidectomy was performed, and the histopathological diagnosis was nodular goiter. Wide excision of the tumor and right proximal humerus was also performed, and the histopathological diagnosis was metastatic follicular thyroid carcinoma. Her TSH and free T4 levels began to normalize after surgery. Postoperatively, she was treated with ^(131)I and has remained free from thyroid cancer recurrence or metastasis. Functioning metastatic lesions from thyroid cancer can present many years after the initial treatment for thyroid cancer, and surgical removal of the metastatic lesions can lead to normalization of thyroid function. Treatment with ^(131)I should be administered to eliminate the possibility of residual tumor.