Abstract
Hyperthyroidism in patients with thyroid cancer is rare although increasingly reported. We describe an unusual case of hyperthyroidism associated with metastatic thyroid cancer presenting as flaccid paralysis. A 53-year-old man with a history of a goiter presented to our hospital with severe low back pain for 1 month and inability to walk. He experienced loss of sensation and motor strength in his legs a few days prior to admission. Of note, he was informed about a neck mass years ago, but elected not to follow-up with any medical providers. MRI and CT imaging revealed a large mediastinal mass with cervical lymphadenopathy and multiple lytic lesions in the spine (T11, L1, L5), right ilium, lung, and liver. Initial labs showed mild hyperthyroidism. Biopsy of a right cervical lymph node revealed metastatic thyroid carcinoma, favoring follicular variant of papillary thyroid carcinoma. His hospital course was further complicated by bowel perforation and atrial fibrillation, requiring amiodarone to control his tachyarrhythmia. Subsequent labs revealed worsening thyrotoxicosis with free T4 of 7.62 ng/dL, free T3 of 14.55 pmol/L, and negative thyroid antibodies. He was a poor surgical candidate and unable to receive radioiodine for diagnosis or treatment due to his recent iodine exposure. Methimazole and PTU were not administered as he was strict NPO due to concerns of worsening his bowel perforation. Instead, he received high-dose dexamethasone for both his spinal cord compression and hyperthyroidism. After extensive goals of care discussion, he was eventually transitioned to hospice care. Hyperthyroidism associated with thyroid cancer is rare, as these cancers are typically hypo-functioning and suppression of thyrotropin helps decrease cancer progression. However, these cases are increasingly described in the literature, with a recent systematic review reporting 28 cases of hyperthyroidism in metastatic thyroid cancer patients. Among patients with thyroid cancers, hyperthyroidism can arise from the primary lesion, metastatic lesions, underlying Graves’ disease, toxic nodules, or even precipitated by a large iodine load. The etiology of hyperthyroidism in our patient is unconfirmed, but given the degree of his thyrotoxicosis, we suspect it was primarily from his metastatic disease and worsened by iodinated contrast and/or amiodarone. Our case highlights the importance of monitoring thyroid hormone levels in patients with thyroid cancers and the consequence of using iodine-containing medications, which can precipitate thyroid hormone dysfunction and delay appropriate treatments such as radioiodine ablation.
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