Concurrent thoracic pathology identified with radiology in hyperthyroid cats referred for radioiodine therapy

Abstract

Objectives Radioiodine (RAI) treatment for hyperthyroidism is becoming increasingly available in the UK. Pretreatment assessment is commonly performed, as patient handling is limited once RAI has been administered. The aims of this study were to determine the prevalence of thoracic pathology using thoracic radiography in hyperthyroid cats referred for RAI treatment and to determine the value of this technique pretreatment. Methods The hospital databases were searched for hyperthyroid cats referred for RAI treatment at the Feline Centre, Langford Vets, between January 2012 and July 2016. Radiographs were reviewed by Diplomates of the European College of Veterinary Diagnostic Imaging at the time of treatment and each set of radiographs was subsequently reviewed by one radiologist for the study. Cardiorespiratory signs were recorded, if present, and any change in treatment plan or suitability for RAI treatment was documented. Results Two hundred and fifty-two cats were included in the study. Thoracic pathology was identified in 77% (n = 194/252) of the cats, of which 59% (n = 115/194) had pulmonary abnormalities with bronchial and bronchointerstitial patterns most frequently; 57% (n = 111/194) had skeletal abnormalities and 43% (n = 84/194) had cardiac abnormalities, with mild-to-moderate cardiomegaly most prevalent. Other abnormalities included sternal lymphadenomegaly (7%; n = 13/194), mediastinal pathology (3%; n = 5/194), oesophageal pathology (2%; n = 4/194) and pleural space disease (0.5%; n = 1/194).Twelve cases (6%) had a change in their treatment plan as a result of thoracic radiographic abnormalities, of which five subsequently underwent RAI treatment. Conclusions and relevance A low prevalence of significant thoracic pathology was identified on radiographs in hyperthyroid cats referred for RAI treatment. Incidental thoracic abnormalities were found much more commonly; hence, results of thoracic radiology need to be combined with the clinical picture, to decide whether further investigations or alterations to the treatment plan are required pre-RAI.

Association between feline hyperthyroidism and thoracic radiographic evaluation of cardiomegaly and pulmonary hyperinflation

“…The only pulmonary pattern found in hyperthyroid cats in this study was a bronchial pattern, as opposed to a previous study, which found bronchial, bronchointerstitial, interstitial, alveolar, nodular, vascular and mixed patterns in hyperthyroid cats presenting for radio iodine therapy. 4 In addition, only 13/52 (25%) of the hyperthyroid cats in this study had an abnormal pulmonary pattern, whereas 115/194 (59%) of the cats in the previous study had an abnormal pulmonary pattern. However, when excluding other types of pulmonary patterns, the prevalence of a bronchial pattern was similar between our study (n = 13/52; 25%) and the previous study (n = 40/194; 21%).…”

“…With the addition of subjective evaluation of cardiomegaly, and testing for inter-and intra-observer agreement for such subjective measures, a significant association may be found between hyperthyroidism and cardiomegaly, as previously reported. 3,4,14 The results of this study indicate that pulmonary hyperinflation is not identified more commonly in hyperthyroid cats than non-hyperthyroid cats. As there is no significant association between hyperthyroidism and pulmonary hyperinflation, hyperthyroidism is an unlikely differential for radiographic pulmonary hyperinflation.…”

“…With the addition of subjective evaluation of cardiomegaly, and testing for inter- and intra-observer agreement for such subjective measures, a significant association may be found between hyperthyroidism and cardiomegaly, as previously reported. 3,4,14…”

“…3 Pulmonary hyperinflation was not specifically assessed in a recent study that investigated radiographic thoracic pathology in hyperthyroid cats presenting for radioiodine therapy. 4 Outside of hyperthyroidism, pulmonary hyperinflation is commonly seen in cats with feline asthma and chronic bronchitis. [5][6][7] In addition, there are few additional reports of diffuse pulmonary hyperinflation in cats including a cat with tracheal anaplastic squamous cell carcinoma 8 and in cats experimentally infected with Dirofilaria immitis.…”

“…[10][11][12][13] Cardiomegaly has also been reported on thoracic radiographs in hyperthyroid cats. 3,4,14 The aim of this study was to describe the radiographic pulmonary and cardiac abnormalities in cats affected with hyperthyroidism. Given that respiratory signs are not common with hyperthyroidism, and that pulmonary hyperinflation is a non-specific and relatively uncommon finding in the veterinary field, we hypothesized that there would be no significant association between hyperthyroidism and radiographic pulmonary hyperinflation.…”