A case of thyroid hormone resistance with thyroid regrowth: implications of misdiagnosis on patient care

Abstract We present the case of a male patient misdiagnosed with resistant hyperthyroidism who erroneously underwent total thyroidectomy complicated by thyroid tissue regrowth. Subsequent iodine-131 (I-131) radiation therapy and medical management further confounded the misdiagnosis. Serological examination in the following years revealed persistently elevated thyroid stimulating hormone (TSH) levels ranging from 45.7 μIU/mL (SI: 45.7 mIU/L) to 134.0 μIU/mL (SI: 134.0 mIU/L) (reference range, 0.550-5.00 μIU/mL SI: 0.55-5.00 mIU/L) with variable free thyroxine (FT4) levels ranging from 0.80 ng/dL to 8.1 ng/dL (SI: 10.3 pmol/L to 104.3 pmol/L) (reference range, 0.90-1.70 ng/dL SI: 11.5-21.8 pmol/L). Thyroid hormone resistance syndromes (RTH) are characterized by thyroid hormone resistance in organ tissues. Clinical presentation varies based on the severity of thyroid hormone dysregulation and the location of hormone resistance. RTH is often misdiagnosed due to variable phenotypic and biochemical presentations, resulting in erroneous medical and surgical treatments that further complicate patient management. The purpose of this report is to highlight the complex treatment course of this patient and describe challenges faced when diagnosing and managing RTH.