Natalie V Watson*, Kate J Bradley, Jane K Murray, Angie Hibbert

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference Contribution (Conference Proceeding)


Objectives: To evaluate the ultrasonographic size and structure of thyroid glands in hyperthyroid cats undergoing radioiodine treatment, and investigate association with serum thyroxine (TT4) levels and duration of disease. Methods: Data were collected prospectively, and case records reviewed for duration of disease and TT4 levels. Cases were defined as having mild (TT4 60 to ≤124 nmol/L), moderate (TT4 125–250 nmol/L) or severe (TT4 3251 nmol/L) hyperthyroidism. Thyroid ultrasound was performed by a board certified radiologist to assess structural features. Thyroid volume was calculated using the rotation ellipse formula [volume (mm3)=length (mm)x width (mm)x height (mm)x TT/6]. Results were analysed descriptively and using Pearson’s correlation (P<0·05). Results: There were 38 cats (15 male, 84% mixed‐breed, age 9–16 years). There were 11 mild [median TT4 94·3 nmol/L (IQR: 80·8–107·8)], 16 moderate [median TT4 165·5 nmol/L (IQR: 143·5–187·5)] and 11 severe [median 310 nmol/L (IQR: 289·5–339·5)] cases of hyperthyroidism. Total thyroid volume tended to increase with disease severity [mild (median 508·28 mm3, IQR: 176·18–840·38), moderate (median 638·21 mm3, IQR: 395·06–881·37), severe (median 823·29 mm3, IQR: 323·75–1322·83)]. A strong, positive linear relationship was observed between TT4 level and total thyroid volume (r=0·633, P<0·001) and between duration of disease and total thyroid volume (r=0·647, P<0·001). Thyroid shape and echogenicity was altered in 55·3% and 76·3% of cases, respectively. Heterogeneity, increased vascularity, mineralisation and thyroid capsule disruption were present in 60·5%, 57·9%, 7·9% and 2·6% of cases, respectively. 28·9% of cases had cystic thyroid glands (mean 1·8 cysts/case). Statement: Increased duration and severity of hyperthyroidism is associated with increased thyroid gland volume, which may require higher radioiodine doses and longer hospitalisation times to treat.
Original languageEnglish
Title of host publicationjournal of small animal practice
Publication statusPublished - 15 Jun 2017

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