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.
|Title of host publication||journal of small animal practice|
|Publication status||Published - 15 Jun 2017|