[Inappropriate TSH: from common etiologies to the rare TSH secreting pituitary adenoma].

Dealing with a patient with hyperthyroidism and goiter, the association of high values of free T4 or free T3 with a normal TSH, may suggest the presence of errors in the measurement as well as the possibility of a TSH secreting pituitary adenoma. However, a very similar clinical picture may occur in the syndrome of resistance to thyroid hormone. The differential diagnosis is made by history and appropriate laboratory tests before considering pituitary imaging. The sole measurement of TSH cannot allow the diagnosis of a TSH secreting adenoma, of which the work-up and treatment are discussed. A similar situation may occur in laboratory medicine, where the doctor has to be puzzled by a inappropriate level of TSH with a high free T4, requiring the establishment of an etiology with a logical approach considering the most frequent causes.