[Secondary hypothyroidism with thyrotropic hormone deficiency. Presentation of a case and review of the literature].

A patient with clinical signs of hypothyroidism, low basal serum thyrotropin (TSH) and lack of response to releasing-factor (TRH) is described. The normal secretion of other anterior pituitary hormones both basal and after stimulation tests and the absence of hypophysial sella alterations found with computed axial tomography suggest the presence of a selective idiopathic TSH deficiency. The pituitary origin of this defect has been reported in literature only in five further patients, tested with TRH. The exact pathogenetic mechanism of these cases is still unknown: in the patient observed by the authors unresponsiveness both to TRH and to metoclopramide suggest an absence of TSH-producing pituitary cells or an alteration of the mechanism beyond the receptor and within the cell. However the possibility that such a secretion defect may represent a first sign of a pituitary tumor should not be excluded.