Pituitary enlargement in post-surgical hypothyroidism misdiagnosed as thyrotroph neoplasia. Report of a case.

Primary hypothyroidism may be associated with enlargement of the sella turcica, due to thyrotroph hyperplasia, in its turn due to the lack of feedback control by thyroid hormones. It may develop independently of the severity or of the duration of thyroid failure. A 42-year-old woman was referred to us. She presented us with a CT scan compatible with a pituitary microadenoma, in the left part of the sella. The patient showed obvious signs of myxedema, due to subtotal thyroidectomy which had been performed 14 months before, because of the presence of multinodular goiter. After operation, the patient has been discontinuously and inappropriately treated with desiccated thyroid. She complained of headache, nausea, galactorrhea without amenorrhea. Serum T4 (0.8 micrograms/dl), serum T3 (47 ng/dl) and TSH (174.5 +/- 60.1 mU/l: M +/- SD of 4 assays) were compatible with primary hypothyroidism as confirmed by TSH hyper-response to i.v. TRH (200 micrograms) and i.v. domperidone (10 mg), and by the normal TSH decrease after orally administered 2.5 mg bromocriptine or 90 min continuously infused 800 micrograms GHIRH. Moreover, an abnormal GH response to TRH was observed, whereas basal and appropriately stimulated PRL levels were normal. Serum alpha-subunit was marginally high (5.92 ng/ml), but alpha-subunit/TSH molar ratio fell within the normal range (0.1 molar ratio). Complete suppression of basal and TRH stimulated TSH values was achieved after a 14-day L-T3 (120 micrograms per day) and 4-month L-T4 (200 micrograms per day) administration. L-T4 treatment, first administered at suppressive doses (200 micrograms per day for 4 months) and subsequently at substitutive doses (150 micrograms per day for 2 months), induced complete remission of symptoms along with normalization of the CT scan picture.