RT Journal Article SR Electronic T1 Challenging diagnosis of resistance to thyroid hormone in a patient with pituitary adenoma JF BMJ Case Reports JO BMJ Case Reports FD BMJ Publishing Group Ltd SP e229430 DO 10.1136/bcr-2019-229430 VO 12 IS 7 A1 Nelson Carvalho Cunha A1 Leonor Gomes A1 Margarida Bastos YR 2019 UL http://casereports.bmj.com/content/12/7/e229430.abstract AB The elevation of thyroid hormone with a normal or elevated thyroid-stimulation hormone (TSH) occurs uncommonly. This set a diagnosis challenge between TSH-secreting pituitary adenoma and resistance to thyroid hormone (RTH). We report a case of a young female patient with palpitations, with elevated thyroid hormone and non-suppressed TSH. TSH receptor antibody was undetectable. Thyroid ultrasound revealed mild heterogeneous goitre, and MRI revealed a microadenoma with 7.5 mm length in pituitary’s left lobe. Pituitary hormones were within normal ranges. The thyrotropin-releasing hormone stimulation test showed normal TSH elevation, consistent with RTH. The genetic test revealed a mutation in heterozygosity in THRB gene (G344R) confirming RTH-beta. No pituitary surgery or thyroidectomy was performed nor were prescribed any antithyroid drugs. Inappropriate secretion of TSH requires a high level of clinical suspicion and the proper laboratory, genetic and radiological studies to conduct a correct diagnosis and prevent unnecessary and potential harmful therapies.