Radioactive iodine uptake in hyperthyroid cats after administration of recombinant human thyroid stimulating hormone

• Published in: Journal of veterinary internal medicine Vol. 32; no. 6; pp. 1891 - 1896
• Main Authors: Oberstadt, Amy E., Nelson, Nathan C., Claude, Andrew K., Refsal, Kent R., Scott‐Moncrieff, J. Catharine, Petroff, Brian K., Langlois, Daniel K.
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.11.2018
• Subjects: 123I; 131I; Animals; blood serum; Cat Diseases - metabolism; Cats; cross-over studies; Female; goiter; humans; hyperthyroidism; Hyperthyroidism - metabolism; Hyperthyroidism - veterinary; Immunoglobulins, Thyroid-Stimulating - pharmacology; iodine; Iodine Radioisotopes - metabolism; Male; neoplasms; Prospective Studies; Random Allocation; Recombinant Proteins; scintigraphy; SMALL ANIMAL; therapeutics; therapy; Thyrogen; Thyroid Gland - metabolism; thyroid hormones; thyrotropin; 123I; Thyrogen; hyperthyroidism; 131I; scintigraphy; therapy
• ISSN: 0891-6640; 1939-1676; 1939-1676
• DOI: 10.1111/jvim.15295

Background Radioactive iodine therapy is considered the treatment of choice for hyperthyroidism in cats, but the availability of this modality is limited by costs and hospitalization requirements. Administration of recombinant human thyroid stimulating hormone (rh‐TSH) to humans with thyroid neoplasia or nodular goiter can increase thyroidal iodine uptake, thereby allowing the use of lower radioactive iodine doses for treatment. Veterinary studies of this subject are limited, and results are conflicting. Objective To investigate the effects of rh‐TSH administration on thyroidal iodine uptake in hyperthyroid cats. Animals Ten client‐owned hyperthyroid cats. Methods In this prospective clinical study, cats were administered saline (placebo), 50 μg rh‐TSH (low‐dose), and 100 μg rh‐TSH (high‐dose) in randomized crossover design with treatments separated by 7‐10 days. After each treatment, thyroid scintigraphy was performed by administering 300 μCi 123I and assessing radionuclide uptake 8 and 24 hours later. Serum thyroid hormone concentrations were measured at each visit. Results Thyroidal percent iodine uptakes (mean ± SD at 8 and 24 hours) in cats treated with placebo (25.2 ± 13.4%, 30.0 ± 12.8%), low‐dose (24.1 ± 12.5%, 29.4 ± 13.7%), and high‐dose rh‐TSH (24.2 ± 16.3%, 30.8 ± 15.3%) were not different (P = .76). Independent of rh‐TSH administration, percent iodine uptakes were positively correlated with serum thyroid hormone concentrations. Conclusions and Clinical Importance One‐time administration of rh‐TSH, even at high doses, would not be expected to lower radioactive iodine doses needed for treatment of hyperthyroidism in cats. Investigations of alternate strategies to increase thyroidal uptake of radioactive iodine are warranted.