Investigation of two methods for assessing thyroid-lobe asymmetry during pertechnetate scintigraphy in suspected hyperthyroid cats.
Our aim was to investigate thyroid:thyroid (T:T) ratio and visual inspection for assessing thyroid-lobe asymmetry in suspected hyperthyroid cats. Although thyroid-salivary asymmetry is a preferred test, inherent thyroid symmetry may assist image interpretation. Association was determined using a scatter plot and Spearman's rank correlation. Agreement was assessed using the kappa (K) statistic. Accuracy was assessed by sensitivity and specificity. Hyperthyroidism was diagnosed in 33/48 (69%) cats based on elevated serum total thyroxine level. Using two Wilcoxan rank-sum tests, a significant difference (P < 0.0001) was detected between cats with and without hyperthyroidism for both methods of assessing thyroid symmetry. For the 18 cats with T:T ratios < or = 1.5, there was poor correlation between the two methods (r(s) = 0.39). Using a cut-point of 1.5 for the T:T ratio, the test accurately predicted hyperthyroidism in 28/33 cats (sensitivity, 85%; 95% confidence interval (CI), 71-99%) and correctly predicted that hyperthyroidism was absent in 14/15 cats (specificity, 93%; CI, 77-100%). For visual inspection, agreement for diagnosing hyperthyroidism was excellent between methods (kappa = 0.82), within the same examiner (weighted kappa = 0.85) and between examiners (weighted kappa = 0.89). Considering cats with only definitely asymmetric thyroid lobes as positive, visual inspection accurately predicted hyperthyroidism in 28/33 cats (sensitivity, 85%; CI, 71-99%) and correctly predicted that hyperthyroidism was absent in 11/15 cats (specificity, 73%; CI, 48-99%). Thyroid-lobe asymmetry occurs more frequently in hyperthyroid than in euthyroid cats but caution should be exercised because some euthyroid cats have asymmetric thyroid glands.
Scrivani
Peter V
PV
Department of Clinical Sciences, Cornell University, College of Veterinary Medicine, Ithaca, NY 14853, USA. pvs2@cornell.edu
Dykes
Nathan L
NL
Page
Richard B
RB
Erb
Hollis N
HN
D000818:Animals; D002371:Cat Diseases / Q000000981:diagnostic imaging*; D002415:Cats; D006980:Hyperthyroidism / Q000000981:diagnostic imaging / Q000662:veterinary*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011877:Radionuclide Imaging / Q000662:veterinary; D019275:Radiopharmaceuticals; D012469:Salivary Glands / Q000000981:diagnostic imaging*; D012680:Sensitivity and Specificity; D013670:Sodium Pertechnetate Tc 99m; D013961:Thyroid Gland / Q000000981:diagnostic imaging*
D019275:Radiopharmaceuticals; D013670:Sodium Pertechnetate Tc 99m