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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
Author(s) -
Peterson Mark E.,
Guterl Jade N.,
Rishniw Mark,
Broome Michael R.
Publication year - 2016
Publication title -
veterinary radiology and ultrasound
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.541
H-Index - 60
eISSN - 1740-8261
pISSN - 1058-8183
DOI - 10.1111/vru.12360
Subject(s) - medicine , euthyroid , thyroid , pertechnetate , cats , scintigraphy , thyroid disease , triiodothyronine , gastroenterology , endocrinology , thyroid stimulating hormone , nuclear medicine
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 (T 4 ), triiodothyronine (T 3 ), free T 4 (fT 4 ), 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 T 4 ( r = 0.76 vs. 0.64), T 3 ( 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.