Thyroid Hormone Resistance With Concurrent Papillary Thyroid Cancer

Introduction: Thyroid hormone resistance is a genetic mutation resulting in decreased receptor responsiveness. We present a case of thyroid hormone resistance with concurrent papillary thyroid cancer. Clinical Case: A 34-year-old man with a history of papillary thyroid carcinoma status post total thyroidectomy and radioactive iodine. He had transferred his care after moving to our area. He presented with persistently elevated TSH despite ongoing treatment with Levothyroxine 400 mcg daily. Upon presentation the patient reported intermittent palpitations and tremor. Vital signs revealed height of 74 inches, weight of 235 pounds, blood pressure of 112/64, and heart rate of 48. Physical examination revealed a well -healed scar on the neck without palpable lymphadenopathy. Bloodwork revealed TSH of 15.28 mIU/L and Free T4 of 2.8 ng/dL. The patient was maintained on Levothyroxine 400 mcg daily and educated on proper administration of the medication. Two months later, bloodwork revealed a TSH of 9.22 mIU/L with a Free T4 of 3.3 ng/dL. MRI of the pituitary revealed a 4mm hyper-intensity which likely represented a microadenoma. Resistance Thyroid Hormone (RTH) Mutation analysis was ordered which revealed a heterozygous mutation for the Thyroid Hormone Receptor (THR)-Beta gene. The mutation was detected at pArg438His indicating a single nucleotide substitution leading to the replacement of arginine by histidine at the p.438 of the translated protein on exon 10. The patient was maintained on Levothyroxine at 400 mcg daily. Discussion: Thyroid hormone resistance describes a constellation of symptoms from decreased tissue responsiveness to thyroid hormones. Literature reveals the prevalence of THR to be 1 in 40,000 individuals. It occurs due to mutation on the thyroid hormone receptor, most often found on the alpha or beta subunit. Frequently patients present with tachycardia and hyperactivity but it can also present with symptoms suggestive of hypothyroidism and goiter. Risk factors include family history of RTH mutation often with an autosomal dominant inheritance pattern. Patients with an elevated Free T4 with a non-suppressed TSH should be investigated with a genetic analysis of Resistance Thyroid hormone. A positive mutation would confirm the diagnosis. Close monitoring of symptoms as well as thyroid function tests should guide treatment. The concurrent diagnosis of thyroid hormone resistance in conjunction with papillary thyroid carcinoma in our patient is unique and makes management a challenge. The literature reveals few cases reported. Reference: DynaMed. (2018, November 30). Thyroid Hormone Resistance. Retrieved October 2, 2020, from https://www-dynamed-com.arktos.nyit.edu/topics/dmp~AN~T912485 Igata M, et al. Coexistence of resistance to thyroid hormone and papillary thyroid carcinoma. Endocrinol Diabetes Metab Case Rep. 2016;2016:160003. doi:10.1530/EDM-16-0003