TSH adenoma and syndrome of resistance to thyroid hormones—Two cases report of syndrome of inappropriate secretion of thyrotropin

SITSH (syndrome of inappropriate secretion of thyrotropin) is a rare clinical state defined as uninhibited serum thyroid stimulating hormone in the presence of elevated thyroid hormone. This state is complicated and mainly caused by the abnormal feedback of hypothalamus–pituitary thyroid axis. The TSH adenoma (TSH‐oma) and resistance to thyroid hormones (RTH) are the main etiologies of SITSH. As is well known that the treatment strategies of RTH and TSH‐oma are apparently different, thus identifying the difference between RTH and TSH‐oma is of great significance for the diagnosis and treatment of SITSH. CASE DESCRIPTION: A 62‐year‐old man with a state of elevated thyroid hormones and inappropriate elevated serum TSH level was hospitalized in 2016. Results of the pituitary enhanced magnetic resonance imaging and the somatostatin test respectively demonstrated a space‐occupying lesion of pituitary and an elevated serum sex hormone binding globulin (SHBG) and inhibited TSH secretion, which indicated the occurrence of TSH‐oma. In 2019, a 23‐year‐old girl with a state of elevated thyroid hormones and inappropriate normal serum TSH was hospitalized. Interestingly, whole exome sequencing detection suggested a pathogenic mutation in thyroid hormone receptor β (THRB) gene, which has been shown to be associated with RTH. CONCLUSIONS: The difference between TSH‐oma and RTH ought to be clarified for their accurate diagnose and treatment. The clinical experiences of the two cases reported here suggest that more detail information such as family medical history, serum SHBG level, and THRB gene test is helpful for the diagnose and treatment of TSH‐oma and RTH. Additionally, we also summarized the identification points, diagnosis process, and treatment strategies for these two rare diseases.