A case of thyroid hormone resistance with coincidental pituitary macroadenoma

Central hyperthyroidism can be a diagnostic challenge, and most commonly arises from a thyrotropin-secreting pituitary adenoma (TSHoma) or thyroid hormone resistance (RTH). Assay interference from heterophile antibodies can also produce spurious biochemical results that mimic these conditions. Accurate distinction between these entities is essential as management strategies differ substantially. We present the case of a 35-year-old man with central hyperthyroidism in the context of a large pituitary macroadenoma, initially suggestive of a TSHoma. Comprehensive biochemical evaluation, dynamic testing and subsequent genetic testing, identified a heterozygous autosomal dominant THRB pathogenic variant (Val458Ala), confirming the diagnosis of RTH and thereby avoiding unnecessary pituitary surgery.