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Hyperthyroidism due to a Pituitary Adenoma Composed of Two Different Cell Types, One Secreting -Subunit Alone and Another Cosecreting -Subunit and Thyrotropin^*

Department of Clinical and Biological Sciences, University of Turin (M.T., F.O., P.P., A.A.), Milan, Italy
The CNR Center of Cytopharmacology, Department of Pharmacology (M.B.) Milan, Italy
The Institute of Endocrine Sciences (G.M., D.C., P.B.-P.), University of Milan Milan, Italy

Address all correspondence and requests for reprints to: Massimo Terzolo, M.D., Patologia Medica, Dipartimento di Scienze Cliniche e Biologiche, Ospedale S. Luigi Gonzaga, Regione Gonzole 10, 10043 Orbassano (TO), Italy.

A 37-yr-old female presented with clinical signs and symptoms of mild hyperthyroidism, high serum levels of free T₄ (24.2 pmol/L), free T₃ (11.7 pmol/L), and sex hormonebinding globulin (157 nmol/L) as well as measurable (by immunofluorometric assay) serum TSH concentrations (1.9 mU/ L) in the absence of any known methodological interference. The above finding indicated the presence of hyperthyroidism due to inappropriate secretion of TSH, whose neoplastic origin was documented by computed tomographic scan showing a 1-cm pituitary adenoma. The diagnosis was confirmed by elevated asubunit levels (9.2 µg/L) and -subunit/TSH molar ratio (25.2) as well as absent TSH suppression after T₃ administration. TRH injection (200 µg, iv) caused impaired TSH (from 3.0 to 4.8 mU/L) and unexpectedly exaggerated -subunit (from 8.8 to 18.2 ng/L) responses. Such a discrepancy was also observed after other dynamic tests.

Double gold particle immunostaining of the adenomatous tissue removed at surgery showed that all of the cells contained secretory granules positive for -subunit, while very few cells were positive for TSHβ and -subunit. In conclusion, the present study demonstrates the existence of TSH-induced hyperthyroidism due to a pituitary adenoma composed of two different cell types: one secreting -subunit alone and another cosecreting -subunit and TSH.

^* This work was supported in part by grants from Ministero della Pubblica Istruzione and CNR (Rome, Italy).

Received May 7, 1990.

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