Dog with a Functional Intra-Thoracic Thyroid Tumour

Malik R.

J Small Anim Pract, 2007. 48(8): p.474; author reply 474.

MADAM

I enjoyed reading the fascinating case study by Stassen and colleagues (2007) in the May 2007 issue of JSAP concerning a dog with a functional intra-thoracic thyroid tumour. The diagnostic investigation was logical and rigorous.

I was disappointed, however, that the owners elected not to pursue “the proposed surgical treatment and the dog was euthanased two months later”. I presume the issue was not the cost of surgery, as the diagnostic investigation was technologically complete (computed tomography, scintigraphy, ultrasound, fine needle biopsy, dynamic endocrine testing etc) and therefore likely to have been expensive. So I presume the owner had “issues” subjecting an eleven-year-old dog to major thoracic surgery.

Since the tumour was functional, and therefore was likely to have taken up radioiodine, would not a single large dose of I-131 been an attractive therapeutic option? Radioiodine therapy has been shown to be effective in treating many thyroid tumours in dogs, including those that are non-functional (Adams and others 1995, Worth and others 2005, Turrel and others 2006).

Failing that, may the dog have benefited from the palliative administration of methimazole or carbimazole to control the endocrine aspects of its disease?

THE AUTHOR RESPONDS:

We were very pleased to read Professor Malik’s positive comments on our article (Stassen and others 2007). It was interesting to (re)read the publications mentioned, particularly the article by Turrel and others (2006). In that article there is also a description of a dog with a mediastinal hyperfunctioning thyroid tumour. The article appeared after submission of our report.

Professor Malik draws our attention to radioiodide therapy as an effective treatment of thyroid tumours in dogs. We are certainly aware of this option (Rijnberk 1966), and have found it particularly useful in difficult surgical candidates such as ectopic carcinomas involving the base of the tongue. The close attachment of these tumours to the hyoid apparatus and the tongue, as well as the abundant neovascularization may prohibit complete surgical resection (Rijnberk 1996).

In our Jack Russell terrier the intrathoracic mass was well circumscribed and therefore we felt it justifiable to suggest surgical resection. However, the owners elected not to undertake any treatment (including radioiodide therapy) because of the severity (in their perception) of the condition. We do not know of any report on the possible beneficial effects of antithyroid drugs in dogs with hyperfunctioning thyroid tumours. This option was not considered, but it might be worth trying in some cases