A Case of Hyperthyroidism Due to Pituitary Resistance to Thyroid Hormone

Abstract

A fifteen-year-old male was admitted to our hospital because his thyroid function showed a lack of TSH suppression in the face of elevated thyroid hormone. This patient complained of heat intolerance, palpitation and hand tremor. Peripheral indices of thyroid hormone action indicated a hypermetabolic state. Serum TSH did not respond sufficiently to TRH stimulation, suggesting TSH-secreting pituitary adenoma. However, sellar CT scan and MRI images did not demonstrate any pituitary adenoma. Moreover, the serum TSH α-subunit concentration was not high and serum TSH was partially suppressed by the administration of T₃. Furthermore, the results of single stranded conformation polymorphism (SSCP) suggested the existence of mutation(s) in the exon 7 of T₃ receptor β (TRβ) gene of this patient. These findings support the diagnosis of pituitary resistance to thyroid hormone.