[Impact of L-thyroxine replacement therapy on pituitary changes secondary to congenital primary hypothyroidism--three cases report].

The aim of the study was an evaluation of the impact of L-thyroxine substitution therapy on the size and structure of the pituitary gland using MRI in three patients with pituitary hyperplasia or tumor secondary to primary congenital hypothyroidism. Along with imaging studies (MRI, skull X-rays) all patients had performed hormonal tests. All hormones (except adrenocorticotropic hormone) of anterior pituitary lobe were measured in basal condition, and some of them (GH, PRL) after stimulation tests, which showed hyperprolactinemia in one case and pituitary somatotropin insufficiency in the other. Only in one out of three patients the regression of the pituitary enlargement was complete, whereas in second case the regression was partial and in third patient evaluation revealed no changes on the MRI. Correct L-thyroxine therapy prevents enlargement of pituitary gland and may regress these changes, but is not the only outcome of pituitary enlargement. Those results shows, that other coexisting disturbances like TSH-secreting adenoma or thyroid hormone resistance must be considered when the treatment is not successful.