title: EVALUATION OF QUANTITATIVE THYROID SCINTIGRAPHY FOR DIAGNOSIS AND STAGING OF DISEASE SEVERITY IN CATS WITH HYPERTHYROIDISM: COMPARISON OF THE PERCENT THYROIDAL UPTAKE OF PERTECHNETATE TO THYROID-TO-SALIVARY RATIO AND THYROID-TO-BACKGROUND RATIOS.
abstract: Thyroid scintigraphy is commonly used for evaluation of cats with hyperthyroidism, with the thyroid-to-salivary ratio (T/S) being the most common method to quantify the degree of thyroid activity and disease. Calculation of thyroid-to-background ratios (T/B) or percent thyroidal uptake of (99m) TcO(-) 4 (TcTU) has only been reported in a few studies. The purpose of this prospective, cross-sectional study was to evaluate a number of quantitative scintigraphic indices as diagnostic tests for hyperthyroidism, including the T/S, three different T/B, TcTU, and estimated thyroid volume. Of 524 cats referred to our clinic for evaluation of suspected hyperthyroidism, the diagnosis was confirmed (n = 504) or excluded (n = 20) based on results of a serum thyroid panel consisting of thyroxine (T4 ), triiodothyronine (T3 ), free T4 (fT4 ), and thyroid-stimulating hormone (TSH) concentrations. In the hyperthyroid cats, median values for TcTU, T/S, and three T/B ratios were all significantly higher (P < 0.001) than values in euthyroid suspect cats or clinically normal cats. All scintigraphic parameters were relatively sensitive and specific as diagnostic tests for hyperthyroidism, but the T/S ratio had the highest test accuracy. The T/S ratio correlated strongly with the TcTU (r = 0.85). However, the TcTU had a higher and more significant correlation (P < 0.01) with serum T4 (r = 0.76 vs. 0.64), T3 (r = 0.77 vs. 0.64), and estimated thyroid volume (r = 0.62 vs. 0.38). Overall, calculation of TcTU is an accurate diagnostic test, but also appears to be the best parameter to predict the functional volume and metabolic activity of the feline adenomatous thyroid gland.
authors.affiliation: Animal Endocrine Clinic, New York, NY, 10025.|Cornell University College of Veterinary Medicine, Ithaca, NY, 14853.
authors.forename: Mark E
authors.identifier: http://orcid.org/0000-0002-3016-1855
authors.initials: ME
authors.lastname: Peterson
authors.affiliation: Animal Endocrine Clinic, New York, NY, 10025.
authors.forename: Jade N
authors.initials: JN
authors.lastname: Guterl
authors.affiliation: Cornell University College of Veterinary Medicine, Ithaca, NY, 14853.
authors.forename: Mark
authors.initials: M
authors.lastname: Rishniw
authors.affiliation: Advanced Veterinary Medical Imaging, Tustin, CA, 92780.
authors.forename: Michael R
authors.initials: MR
authors.lastname: Broome
mesh_terms: D000818:Animals; D013956:Antithyroid Agents / Q000008:administration & dosage*; D002371:Cat Diseases / Q000000981:diagnostic imaging*; D002415:Cats; D005260:Female; D006980:Hyperthyroidism / Q000000981:diagnostic imaging / Q000662:veterinary*; D008297:Male; D008713:Methimazole / Q000008:administration & dosage*; D011877:Radionuclide Imaging / Q000662:veterinary*; D012463:Saliva / Q000737:chemistry; D013670:Sodium Pertechnetate Tc 99m / Q000378:metabolism*; D013961:Thyroid Gland / Q000000981:diagnostic imaging* / Q000473:pathology
chemical_list: D013956:Antithyroid Agents; D008713:Methimazole; D013670:Sodium Pertechnetate Tc 99m
keywords: cat; feline; hyperthyroidism; scintigraphy; thyroid gland