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Treatment of Hyperthyroidism Associated with Thyrotropin-Secreting Pituitary Adenomas with Iopanoic Acid

Department of Medicine, Division of Endocrinology, and Gonda Diabetes Center (K.S.D., P.C., C.H.D., I.J.C.), and Department of Surgery (D.F.K.), Division of Neurosurgery, University of California, Los Angeles School of Medicine; University of California, Los Angeles Pituitary Tumor and Neuroendocrine Program (K.S.D., P.C., D.F.K., C.H.D., I.J.C.), Los Angeles, California 90024; and Hoag Memorial Hospital (K.V.I.), Newport Beach, California 92658

Address all correspondence and requests for reprints to: Pejman Cohan, M.D., 200 UCLA Medical Plaza, Suite 530, Los Angeles, California 90095-7065. E-mail: pcohan{at}mednet.ucla.edu.

TSH-secreting tumors comprise less than 2% of all pituitary adenomas. All patients present with hyperthyroidism with a detectable TSH level, and a majority have macroadenomas. Oral cholecystographic agents (e.g. iopanoic acid) potently inhibit the activation of T₄ to the more potent T₃. They have been used successfully to treat primary thyroidal hyperthyroidism and thyroxine overdose. However, they have not been employed in the treatment of central hyperthyroidism. We report, herein, the first two patients with thyrotropinomas, in whom iopanoic acid (Telepaque) has been used perioperatively to safely and rapidly achieve euthyroidism. In case 1, free T₃ index improved from a value of 634 to 175 (normal range 78–162) after 3 d of therapy with iopanoic acid. In case 2, free T₃ by dialysis improved from 697 pg/dl (10.7 pmol/liter) to 195 pg/dl (3.0 pmol/liter) (normal range 210–440 pg/dl; 3.2–6.7 pmol/liter) after 7 d of therapy with iopanoic acid.

Abbreviations: FT3, Free T₃; FT4, free T₄; MRI, magnetic resonance imaging; OCA, oral cholecystographic agent.