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DIAGNOSIS OF FELINE HYPERTHYROIDISM USING THYROID
SCINTIGRAPHY. Marsolais, ME, Mott, J, Berry, CR. Journal of Veterinary Internal Medicine 17: 393 (Research abstract), 2003. Diagnosis of hyperthyroidism is traditionally made by demonstrating elevations in the serum thyroxine (T4) level; however, fluctuations in T4 levels and the possibility that concurrent disease can suppress thyroid hormone concentrations often limit the diagnostic accuracy of this test. Hyperthyroidism has been definitively diagnosed by demonstrating a thyroid to salivary gland (T : S) ratio greater than 1 : 1 using sodium 99mTc-pertechnetate thyroid scintigraphy. The purpose of this study was to evaluate cats with a palpable thyroid nodule and normal serum thyroxine levels (T4 between 1.0–4.0 mg/dL) for the presence of hyperfunctional thyroid tissue based on results of sodium 99mTc-pertechnetate thyroid scintigraphy. This study evaluated 23 cats with a palpable thyroid nodule and normal T4 values. Free T4 by equilibrium dialysis [fT4(ED)] was measured in 16/23 cats. Nuclear scintigraphy was performed on all cats using standard views and imaging parameters. These results were compared with established normal T: S ratios to identify hyperthyroid cats. Cats positive on the basis of scintigraphy (T : S ratio > 1 : 1) were further classified as unilateral, bilateral, or ectopic disease. Data was analyzed using single analysis of variance comparing average T4, average fT4(ED), and prevalence of clinical signs and physical exam findings between the positive and negative scintigraphy groups. A Student’s t-test was used to demonstrate statistical difference in T: S ratios between positive and negative groups. A p value of 0.05 was determined significant. Seventeen of 23 cats (74%) were diagnosed to be hyperthyroid based on thyroid scintigraphy, while the remaining 6/23 were negative. There was no significant difference in serum thyroxine levels between cats in the positive and negative |